grounding a sailboat from lightning

Yachting Monthly

• Digital edition

Sailing in lightning: how to keep your yacht safe

• In partnership with Katy Stickland
• July 22, 2022

How much of a concern is a lightning strike to a yacht and what can we do about it? Nigel Calder looks at what makes a full ‘belt and braces’ lightning protection system

Storm clouds gather at Cowes, but what lightning protection system, if any, does your boat have for anchoring or sailing in lightning? Credit: Patrick Eden/Alamy Stock Photo

Most sailors worry about sailing in lightning to some extent, writes Nigel Calder .

After all, going around with a tall metal pole on a flat sea when storm clouds threaten doesn’t seem like the best idea to most of us.

In reality, thunder storms need plenty of energy, driven by the sun, and are much less frequent in northern Europe than in the tropics.

However, high currents passing through resistive conductors generate heat.

Small diameter conductors melt; wooden masts explode; and air gaps that are bridged by an arc start fires.

Sailing in lightning: Lightning is 10 times more likely over land than sea, as the land heats up more than water, providing the stronger convection currents needed to create a charge. Credit: BAE Inc/Alamy Stock Photo

On boats, radio antennas may be vaporised, and metal thru-hulls blown out of the hull, or the surrounding fiberglass melted, with areas of gelcoat blown off.

Wherever you sail, lightning needs to be taken seriously.

Understanding how lightning works, will help you evaluate the risks and make an informed decision about the level of protection you want on your boat and what precautions to take.

Most lightning is what’s called negative lightning, between the lower levels of clouds and the earth. Intermittent pre-discharges occur, ionising the air.

Whereas air is normally a poor electrical conductor, ionised air is an excellent conductor.

These pre-discharges (stepped leaders) are countered by a so-called attachment spark (streamer), which emanates from pointed objects (towers, masts, or lightning rods) that stand out from their surroundings due to their height.

Summer is the season for lightning storms in the UK. Here, one finds early at Instow, Devon. Credit: Terry Matthews/Alamy Stock Photo

This process continues until an attachment spark connects with a stepped leader, creating a lightning channel of ionised air molecules from the cloud to ground.

The main discharge, typically a series of discharges, now takes place through the lightning channel.

Negative lightning bolts are 1 to 2km (0.6 to 1.2 miles) long and have an average current of 20,000A.

Positive lightning bolts are much rarer and they can have currents of up to 300,000A.

Preventing damage when sailing in lightning

A lightning protection system (LPS) is designed to divert lightning energy to ground (in this case the sea), in such a way that no damage occurs to the boat or to people.

Ideally, this also includes protecting a boat’s electrical and electronic systems, but marine electronics are sensitive and this level of protection is hard to achieve.

Lightning protection systems have two key components: First, a mechanism to provide a path with as little resistance as possible that conducts a lightning strike to the water.

This is established with a substantial conductor from an air-terminal to the water.

Components of an external and internal lightning protection system. Credit: Maxine Heath

This part of the LPS is sometimes called external lightning protection.

Second, a mechanism to prevent the development of high voltages on, and voltage differences between, conductive objects on the boat.

This is achieved by connecting all major metal objects on and below deck to the water by an equipotential bonding system.

Without this bonding system high enough voltage differences can arise on a boat to develop dangerous side flashes.

The bonding system can be thought of as internal lightning protection.

Rolling ball concept

Lightning standards, which apply ashore and afloat, define five lightning protection ‘classes’, ranging from Class V (no protection) to Class I.

There are two core parameters: the maximum current the system must be able to withstand, which determines the sizing of various components in the system, and the arrangement and number of the air terminals, aka lightning rods.

Let’s look at the arrangement of the air terminals first. It is best explained by the rolling ball concept.

A lightning strike is initiated by the stepped leaders and attachment sparks connecting to form the lightning channel.

The distance between the stepped leader and the attachment sparks is known as the breakdown distance or striking distance.

If we imagine a ball with a radius equal to the striking distance, and we roll this ball around an object to be protected, the upper points of contact define the possible lightning impact points that need to be protected by air terminals.

Lightning protection theories and classifications rely on a ‘rolling ball’ concept to define requirements, areas of risk and protected areas. Credit: Maxine Heath

The air terminal will theoretically provide a zone of protection from the point at which the terminal connects with the circumference of the rolling ball down to the point at which that circumference touches the water.

The shorter the striking distance, the less the radius of the rolling ball and the smaller the area within the protection zone defined by the circumference of the rolling ball.

The smaller the protection zone, the more air terminals we need. So, we use the shortest striking distance to determine the minimum number and location of air terminals.

Class I protection assumes a rolling ball radius of 20m; Class II assumes a rolling ball radius of 30m.

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Boat building standards are based on a striking distance/rolling ball radius of 30m (Class II).

For masts up to 30m above the waterline, the circumference of the ball from the point at which it contacts the top of the mast down to the water will define the zone of protection.

For masts higher than 30m above the waterline, the ball will contact the mast at 30m and this will define the limit of the zone of protection.

If Class I protection is wanted, the radius of the ball is reduced to 20m, which significantly reduces the zone of protection and, on many larger recreational boats, may theoretically necessitate more than one air terminal.

Protection classes

With most single-masted monohull yachts, an air terminal at the top of the mast is sufficient to protect the entire boat to Class I standards.

The circumference of the rolling ball from the tip of the mast down to the surface of the water does not intercept any part of the hull or rig.

However, someone standing on the fore or aft deck might have the upper part of their body contact the rolling ball, which tells us this is no place to be in a lightning storm.

Some boats have relatively high equipment or platforms over and behind the cockpit.

Protection classes to protect your boat while anchored or sailing in lightning

These fittings and structures may or may not be outside the circumference of the rolling ball.

Once again, this tells us to avoid contact with these structures during a lightning storm.

Ketch, yawl, and schooner rigged boats generally require air terminals on all masts, except when the mizzen is significantly shorter than the main mast.

The external LPS

The external LPS consists of the air terminal, a down conductor, and an earthing system – a lightning grounding terminal.

The down conductor is also known as a primary lightning protection conductor.

All components must be sized to carry the highest lightning peak current corresponding to the protection class chosen.

In particular, the material and cross-sectional area of the air terminal and down conductor must be such that the lightning current does not cause excessive heating.

The air terminal needs to extend a minimum of 150mm above the mast to which it is attached.

A graph depicting NASA’s record of yearly global lightning events. The Congo once recorded more than 450 strikes per km2

It can be a minimum 10mm diameter copper rod, or 13mm diameter aluminum solid rod.

It should have a rounded, rather than a pointed, top end.

VHF antennas are commonly destroyed in a lightning strike.

If an antenna is hit and is not protected by a lightning arrestor at its base, the lightning may enter the boat via the antenna’s coax cable.

A lightning arrestor is inserted in the line between the coax cable and the base of the antenna.

It has a substantial connection to the boat’s grounding system, which, on an aluminum mast, is created by its connection to the mast.

In normal circumstances, the lightning arrestor is nonconductive to ground.

When hit by very high voltages it shorts to ground, in theory causing a lightning strike to bypass the coax – although the effectiveness of such devices is a matter of some dispute.

Down conductors

A down conductor is the electrically conductive connection between an air terminal and the grounding terminal.

For many years, this conductor was required to have a resistance no more than that of a 16mm² copper conductor, but following further research, the down conductor is now required to have a resistance not greater than that of a 20mm² copper conductor.

For Class I protection, 25mm² is needed. This is to minimise heating effects.

Let’s say instead we use a copper conductor with a cross-sectional area of 16mm² and it is hit by a lightning strike with a peak current corresponding to Protection Class IV.

Sailing in lightning: This catamaran relies upon cabling to ground from the shrouds but stainless steel wire is not a good enough conductor. Credit: Wietze van der Laan

The conductor will experience a temperature increase of 56°C. A 16mm² conductor made of stainless steel (for example, rigging ) will reach well over 1,000°C and melt or evaporate.

Shrouds and stays on sailboats should be connected into a LPS only to prevent side flashes.

The cross-sectional area of the metal in aluminum masts on even small sailboats is such that it provides a low enough resistance path to be the down conductor.

Whether deck- or keel-mounted, the mast will require a low resistance path, equivalent to a 25mm² copper conductor, from the base of the mast to the grounding terminal.

Grounding terminal

Metal hulled boats can use the hull as the grounding terminal. All other boats need an adequate mass of underwater metal.

In salt water this needs a minimum area of 0.1m². In fresh water, European standards call for the grounding terminal to be up to 0.25m².

A grounding terminal must be submerged under all operating conditions.

An external lead or iron keel on monohull sailing boats can serve as a grounding terminal.

This owner of this Florida-based yacht decided to keep the keel out of the equation when is came to a grounding plate. High electrical currents don’t like sharp corners, so a grounding plate directly beneath the mast makes for an easier route to ground. Credit: Malcolm Morgan

In the absence of a keel , the cumulative surface area of various underwater components – propellers, metal thru-hulls, rudders – is often more than sufficient to meet the area requirements for a grounding terminal.

However, these can only be considered adequate if they are situated below the air terminal and down conductor and individually have the requisite surface area.

Metal through-hulls do not meet this requirement.

If underwater hardware, such as a keel, is adequate to be used as the grounding terminal, the interconnecting conductor is part of the primary down conductor system and needs to be sized accordingly at 25mm².

Propellers and radio ground plates

Regardless of its size, a propeller is not suitable as a grounding terminal for two reasons.

First, it is very difficult to make the necessary low-resistance electrical connection to the propeller shaft, and second, the primary conductor now runs horizontally through the boat.

The risk of side flashes within the boat, and through the hull to the water is increased.

Sailing in lightning: GRP hull, fairing filler and iron keel will have carried different voltages during the strike – hence this damage

An engine should never be included in the main (primary) conducting path to a grounding terminal.

On modern engines, sensitive electronic controls will be destroyed in a lightning strike, and on all engines, oil in bearings and between gears will create resistance and therefore considerable heat which is likely to result in internal damage.

However, as it is a large conductive object, the engine should be connected to the internal lightning protection system.

Internal lightning protection

On its way to ground, lightning causes considerable voltage differences in adjacent objects – up to hundreds of thousands of volts.

This applies to boats with a functioning external lightning protection system but without internal protection.

Although the lightning has been given a path to ground along which it will cause as little damage as possible, dangerous voltages can be generated elsewhere, resulting in arcing and side flashes, threatening the boat and crew, and destroying electronic equipment.

We prevent these damaging voltage differences from arising by connecting all substantial metal objects on the boat to a common grounding point.

One of the holy grails of marine photography – a direct lightning strike on a yacht’s mast. Credit: Apex

The grounding terminal is also wired to the common grounding point.

By tying all these circuits and objects together we hold them at a common voltage, preventing the build-up of voltage differences between them.

All conductive surfaces that might be touched at the same time, such as a backstay and a steering wheel, need to be held to the same voltage.

If the voltages are the same, there will be no arcing and no side flashes.

The bonding conductors in this internal LPS need to be stranded copper with a minimum size of 16mm².

Note that there can be bonding of the same object for corrosion prevention, lightning protection, and sometimes DC grounding.

We do not need three separate conductors.

Electronic Device Protection

With lightning protection systems, we need to distinguish electric circuit and people protection from device protection.

Even with an internal LPS, high induced voltages may occur on ungrounded conductors (such as DC positive) which will destroy any attached electronics.

A mechanism is needed to short high transient voltages to ground.

This is done with surge protection devices (SPD), also known as transient voltage surge suppressors (TVSS) or lightning arrestors.

Marine-specific SPDs are few in number and domestic models are not suitable for boats

In normal circumstances these devices are non-conductive, but if a specified voltage – the clamping voltage – is exceeded they divert the spike to ground.

There are levels of protection defined in various standards depending on the voltages and currents that can be handled, the speed with which this occurs, and other factors.

This is a highly technical subject for which it is advisable to seek professional support.

Most SPDs are designed for AC circuits.

When it comes to DC circuits there are far fewer choices available to boat owners although there are an increasing number for solar installations that may be appropriate.

There is no such thing as a lightning-proof boat, only a lightning-protected boat, and for this there needs to be a properly installed LPS.

Nigel Calder is a lifelong sailor and author of Boatowner’s Mechanical and Electrical Manual. He is involved in setting standards for leisure boats in the USA

Even so, in a major strike the forces involved are so colossal that no practical measures can be guaranteed to protect sensitive electronic equipment.

For this, protection can be provided with specialised surge protection devices (SPDs).

The chances of a direct lightning strike on a yacht are very small, and the further we are north or south of the equator, the smaller this chance becomes.

It’s likely your chances of receiving a direct lightning strike are very much higher on a golf course than at sea.

‘Bottle brush’-type lightning dissipators are claimed by sellers to make a boat invisible to lightning by bleeding off static electrical charge as it builds up.

The theory rests upon the concept that charged electrons from the surface of the earth can be made to congregate on a metal point, where the physical constraints caused by the geometry of the point will result in electrons being pushed off into the surrounding atmosphere via a ‘lightning dissipator’ that has not just one point, but many points.

It is worth noting that the concept has met with a storm of derision from many leading academics who have argued that the magnitude of the charge that can be dissipated by such a device is insignificant compared to that of both a cloud and individual lightning strikes.

It seems that the viable choices for lightning protection remain the LPS detailed above, your boatbuilder’s chosen system (if any), or taking one’s chances with nothing and the (reasonable) confidence that it’s possible to sail many times round the world with no protection and suffer no direct strikes.

Whichever way you go, it pays to stay off the golf course!

Enjoyed reading Sailing in lightning: how to keep your yacht safe?

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Sailboat Grounding Systems

• By Steve D'Antonio
• Updated: September 1, 2021

Recently I met with a client to review and critique his vessel’s systems. One item I saw related to the bonding or grounding system. These systems serve similar purposes: to carry stray, galvanic or fault current back to its source.

Let me clarify two related matters. First, electricity does not “seek ground” as so many dockside sages insist. No, whether from a battery or shore power, it seeks to return to its source. One example of the return-to-source concept is all-too-often tragic; it relates to electric-shock drowning, or in-water electrocution. When AC current, which originates from shore power, “leaks” into the water in which the vessel floats, it attempts to return to its origin, which in most cases is a transformer located on the dock or in the marina parking lot. Once power passes through a transformer, that transformer becomes a power source. So if a shore-power transformer is installed aboard a vessel, fault current will seek to return to that transformer—rather than through the water—and on to the one supplying the marina, making it a safer option.

RELATED: The Dos and Don’ts of Boat Wiring

Second, while the terms are frequently and understandably used interchangeably, “bonding” is often used in conjunction with underwater metals and corrosion prevention, while “grounding” often refers to the connection of equipment chassis and hardware to the DC-negative terminal. The two systems are, however, almost always connected (along with the AC safety and lightning ground systems), so for the purposes of this discussion, they are one in the same.

In the case of my client’s boat, I noticed a 14-gauge wire connected to the engine block. It appeared rather new, and when I asked about it, the owner confirmed that an electrician had installed it in the not-too-distant past. A poor block ground can cause oil-pressure and coolant-temperature-gauge issues, which may have been the impetus for adding it. While this “fix” may have solved one problem, it created a fire risk.

Another electrical myth is “electricity takes the path of least resistance.” In fact, electricity takes all paths, with the current flow being proportionate to the resistance. Thus, more current flows through lower-resistance, larger-wire paths; when both are present, larger wires carry more current than smaller wires. But what happens if the larger wire breaks, or is inadvertently disconnected, or the connection loosens or corrodes? In that case, a small-gauge wire connected to an engine block will be called upon to carry high current, such as from a starter or alternator.

A few years ago, I was inspecting the engine room on a 60-footer. A mechanic had recently replaced the batteries, then started the engine to test his work. However, when removing the old batteries, he’d dropped one cable behind a battery box and then failed to reconnect it when installing the new batteries. When he turned the key, instead of flowing through a cigar-size 2/0 cable, the starter current instead took an alternate path through a 12-gauge bonding wire connected to the engine block. A few feet away, I recall feeling the heat on my face as it almost instantly glowed white-hot, and the insulation melted and then burned away. Fortunately, the wire melted before anything caught fire.

It doesn’t take a miss-wire scenario for an event like this to occur. If the starter’s or alternator’s positive cable chafes against the engine block (ABYC standards prohibit starter positive cables from touching the block in any way), current will attempt to return to the battery via all paths, including small bonding wires.

The simple moral? Every grounding/bonding wire connected to the block of an engine or generator, or to any other piece of DC equipment, must be capable of carrying full starting or fault/short-­circuit current, which means it can be no less than one size smaller than the largest DC-positive cable. Furthermore, bonding wires should not be connected to current-carrying parts. If the chassis of the block, thruster, etc., is common with the DC-negative, then it should not be bonded. Engine blocks and gensets that utilize isolated ground starters and alternators may, on the other hand, be bonded.

Steve D’Antonio offers services for boat owners and buyers through Steve D’Antonio Marine Consulting .

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How to Prepare for Lightning Strikes

• By Ken Englert
• Updated: January 24, 2012

Lightning will always take the most direct conductive path to earth by striking the highest object in the area. Unfortunately, on the water, the highest and most attractive object to a lightning bolt just might be your boat. Be advised that when lightning strikes your boat or even near your boat, your electronics are vulnerable to damage. Here’s how to be prepared.

Create a Short Circuit There is no absolute protection against lightning aboard a boat. But there are steps you can take to avoid or minimize damage. The most likely targets are antennas, fishing rods, towers, T-tops or any elevated electrically conductive surface. You can’t prevent a lightning strike, but you can create a safe path for lightning to travel.

To conduct a strike safely to “ground” (on a boat this means to the water), create a low-resistance path from the highest point on your boat to a metal grounding plate in contact with the water. Start with a solid half-inch-diameter steel or bronze rod elevated six to 12 inches above every other object on the boat. The tip of that rod should be pointed, not blunt. Run a conductor made of at least a No. 8 gauge wire from the rod in as straight a path as possible to the water-grounding point.

The recommended water ground is a metal ground plate mounted outside of the hull. It can be copper, monel, naval bronze or other noncorrosive metal and should be solid, not the porous type used for radio antenna grounds, and be at least one square foot in area. Check with the manufacturer to see if this already exists. Also know that factory-installed lightning rods and grounding conductors are sometimes unwisely removed or disconnected by boat dealers or unknowing buyers.

Ground, Ground, Ground Ground all electronics and large metal objects on board, including metal cases or grounding studs on electronics and electrical equipment. Not to be overlooked are the engine(s), stove, sink, tanks, refrigerator, air-conditioner, metal railings, tower, arch and Bimini top. When running grounding conductors, don’t attempt to neatly bundle grounding cables together with the rest of the electrical wiring. Keep them separate from all other conductors, including antenna wires. Also, do not run the ground conductors in close proximity to or parallel to existing wire runs to prevent arcing.

More Detailed Lightning Protection Tips and Strategies

Storm Safety Tips – Lower all antennas and downriggers.

– Disconnect all power, antenna and interconnection cables to the electronics and electrical gear.

– Do not touch two metal surfaces at the same time (engine controls, a railing, helm, etc.) or you may become a convenient conducting path yourself.

– Do get out of the area and head for shore, and send the crew belowdecks.

Check out more tips on how to protect yourself and your boat during a lightning storm: 3 Crucial Tips to Avoid Lightning Strikes

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Protecting Your Boat From Lightning Strikes

Most boat owners have only the vaguest idea of what is involved in protecting their boats from lightning damage. Many believe that their boats are already protected by the boat’s grounding system. Most are wrong.

Just because your boat may be bonded with heavy copper conductors connecting the masses of metal in the boat doesn’t mean that it is protected against lightning. A bonding system may be a part of a lightning protection system, but bonding itself offers no protection to the boat unless a good, direct path to ground is part of the system.

While neither aluminum nor stainless steel is an outstanding electrical conductor, the large cross-sectional area of both the mast and the rigging provide adequate conductivity for lightning protection. The trick, however, is getting the electricity from the mast and rigging to the water.

The straighter the path is from conductor (mast and rigging) to ground, the less likely are potentially dangerous side flashes. Put simply, side flashes are miniature lightning bolts which leap from the surface of the conductor to adjacent metal masses due to the difference in electrical potential between the charged conductor and the near by mass of metal. Ideally, therefore, the path from the bottom of the mast and rigging to ground would be absolutely vertical. In practice, this is rarely achieved.

If the boat has an external metal keel, the mast and standing rigging is frequently grounded to a keelbolt. There are pitfalls to this method. First, the connection between the bottom of the mast and rigging to the keelbolt must be highly conductive. ABYC (American Boat and Yacht Council) standard TE-4 for lightning protection systems require that these secondary conductors have a conductivity at least equal to that of AWG #6 copper-strand cable. There is no drawback to using an even larger conductor.

Connecting the short conductor to the mast and keelbolt presents some problems. A crimp eye can be used on the end that is to be attached to the mast, but you may have to fabricate a larger eye for attachment to the keelbolt. This can be made from sheet copper. Soldering the connections is not recommended, since the heat generated in a lightning strike could melt the solder.

Then you have to face up to a basic problem. Your mast is aluminum, yet you’re connecting it to ground with a copper cable. Everyone knows that aluminum and copper are not galvanically compatible, so what’s the solution? While it will not eliminate corrosion, a stainless steel washer placed between the copper cable’s end fitting and the aluminum mast will at least retard it. But this connection is going to require yearly examination to make sure that a hole isn’t being eaten through the mast. In addition, of course, the process of corrosion creates wonderful aluminum oxide byproducts, which have very low conductivity. The aluminum oxide may reduce conductivity to the point where your theoretical attachment to ground is in fact non-existent. Once again, disassembling the connection and cleaning it yearly are essential to maintain conductivity. Constant attention to all the conductor connections is essential in any grounding system, whether it’s for lightning protection or grounding of the electrical system.

For more information on how to best protect your boat from lightning strikes, purchase Nigel Calder’s Boatowner’s Mechanical & Electrical Manual from Practical Sailor .

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An approach to a modern sailboat lightning protection system

We were lucky when we were struck by lightning on our small 35’ GRP cruising sailing boat in Turkey in 2013, but without an LPS. All the plastic and some of the metal gear at the top of the mast exploded (see photo below) and simultaneously the headlining in the saloon exploded downwards with a loud bang. So much smoke that we initially thought we were on fire; but my wife and I survived unscathed to tell the tale.

The most likely discharge exit was through the propeller shaft, but practically all electronics were violently destroyed and, as an electrical and electronic engineer, my assessment for our insurance claim afterwards showed that most devices had experienced severe arcing with small electronic components having exploded internally (see photo below).

An lightning protection system is a bonding, grounding and shielding arrangement made of four distinct parts: Air terminals, down conductors, a low-impedance ground system and sideflash protection.

The best lightning protection system cannot guarantee personal protection, or protection from damage to sensitive electronic equipment. Also it is not a lightning prevention system. I knew the private owner of one large blue water catamaran which has been struck three times in its life and it is not an old boat. Fortunately no one was hurt on any occasion, but many electronic systems on that complex boat were effected and had to be replaced on each occasion. Unfortunately catamarans are many times more likely to be struck than mono-hulls and records in the USA, where certain locations are particularly prone to electrical storms (e.g. Florida where boat ownership is high), show that mono-hull sailing boats are about 25 times more likely to be struck than motoryachts.

Lightning is very hard to study and to accurately predict its behaviour is almost impossible, but it is driven by the simple fact that a massive potential difference (voltage) exists between the highly charged clouds of a brewing thunderstorm and the surface of the Mother Earth. Eventually, a path is found through the atmosphere down to ground for some of the accumulated charge to discharge and the creation of a discharge path first requires the creation of so called ‘streamers’ [1],[2]. Bear in mind that air breaks down at 3 million Volts per metre, and you get some inkling of the enormous voltage differences involved.

In the middle of a large body of water, with your sailing yacht in it, the top of the mast, being the highest point around, looks like a handy point to discharge through. So the LPS is designed to control the first point of discharge and then make the onward path to ‘ground’ – in this case the sea – as direct as possible and capable of conducting very high currents for a very short time during the discharge.

In 2006, the American Boat and Yacht Council (ABYC) technical information report TE-4 [3], [4] recommended the following:-

• lightning protection system conductors must be straight and direct and capable of handling high currents. The main ‘down’ conductor is recommended to be 4AWG, or 25mm2 in European sizing; see diagram.

• A large enough area ground must be provided between the vessel and the water to offer an adequately low resistance path (ABYC recommends 1sq.ft. {0.1m2} in salt water; much larger in fresh water. NB this is not adequate for acting as the SSB counterpoise). Metal-hulled vessels naturally offer a large ground contact area with the sea, but the connection between the hull and all other electrical systems needs careful consideration.

• Heavy metal objects such as fuel tanks and engines must be bonded to the ground bonding arrangement to reduce the risk of ‘side flashing’ where the lightning literally can jump from one conductor to another, seemingly better path. Similarly, it can jump out of corners in cabling, so if bends must be made, then they should not be more than 90° and with as large a bend radius as possible.

The basic arrangement is as depicted in the diagram, where the ‘air terminal’ is a rounded end (circled in photo) metal wand mounted at the top of the mast to ‘attract’ lightning to it and, most importantly, to stand at least 6” (15cm) higher than anything else e.g. above the VHF or other antenna. Providing the air terminal is securely electrically bonded, presenting a high surface contact area, low resistance path to an aluminium mast, the mast itself can be used as the down conductor at least to the deck or keel, depending on where the mast is stepped. In the case of wooden, or carbon composite masts they present too high electrical resistance and a 4AWG cable must be run straight down the mast as the main down conductor. From the bottom of the aluminium mast or down conductor, the 4AWG onward path needs to be as direct and short as possible to the ground plate, or the metal hull.

It is actually better to leave through-hull metal fittings electrically isolated if they are already insulated from the rest of the boat by dint of their attached rubber or plastic hoses and their insulating mounting plates – decent quality bronze alloy seacocks and engine intake strainers will not unduly corrode if left submerged for extended periods of time without needing connecting to the vessel’s earth bonding. However, in the US it is more normal to bond everything metal below the waterline, use a tinned copper bus bar running the necessary length of the vessel, above any bilge water level, to connect each through-hull fitting to, which is then connected at one point only to the main grounding route out of the boat. This bonding arrangement is gaining in popularity outside the US with consideration of a lightning protection system.

Note in the diagram that all tie-ins, including fore- and back-stay (unless insulated) must use at least 6AWG (16mm2 European) cable. All large metal objects within 6ft (2m) of the lightning down path also need tying in with 6AWG (16mm2) cable. Examples are metal fuel tanks, main engines (despite them usually already being connected to the water via their prop shaft) and generators; this is to minimize the risk of ‘side flashing’ where lighting can literally jump from conductor to metal object, looking for a better path to ground, even if one does not exist.

In considering of the creation of a ground plate of sufficient size, a metal hulled vessel is ideal, but nevertheless only one electrical connection point to the hull should be made from the main 4AWG down conductor. This same point should have all the other earth bonding made to it alone. The DC main negative bus in turn should be connected to the earth bonding in only one place, though European boats generally have their DC system isolated from any bonding system to discourage DC earth faults, the US differs in this respect, preferring direct bonding. One solution to this dilemma is to use a suitably rated surge capacitor between the DC negative busbars and the bonding system for the LPS. In the case of a non-metal hulled sailing vessel, the attraction of using the keel as a discharge point should be resisted as it is in contact with the water some distance below the surface where already a lot is going on with respect to charge balancing, so an alternative point is likely to be sought out by the discharge, nearer the surface. It seemed clear to our very experienced (and ancient) marine insurance surveyor that, during our own strike in Turkey, the discharge was out through the propeller shaft.

So far, so good, but recent thinking and good practice [5],[6] has modified the above ideas to take into consideration the danger of side flashing much more. A side flash is an uncontrolled spark that carries current to the water and can do extensive damage to hulls and equipment. The good practice and standards for a lightning protection system relating to marine situations, such as they exist (see NFPA 780, latest version, especially chapter 8, ‘Protection for Watercraft’, [7]) are tending to treat a boat more and more like a building to exploit those well tried and tested techniques used in a land based situation. Rather than a ‘cone’ below the air terminal, the ‘zone of protection’ is now more reliably envisaged to be formed from a ‘rolling sphere’ of 30m radius, as shown below for a larger yacht [7],[8]:-

Diagram of Boat with Masts in Excess of 15 m (50 ft) Above the Water; Protection Based on Lightning Strike Distance of 30 m (100 ft).

With a large building, the down conductors from the various air terminals run down the outside of the building to a number of grounding stakes; not so with a yacht where, as we have described, we’ve now concentrated the discharge right in the middle of the boat, where the danger of side flashing into other metal parts is very real; if these parts are not bonded and protected by a properly designed, low impedance path there’s are very real further danger of the side flash finding its way onwards and out through the side of the boat to the surrounding water surface. This has indeed been experienced by an American friend of mine on a high-tech, all carbon racing sailing boat on its way back to Newport, which after being unavoidably struck several times in a violent storm, put in to New York and immediately hauled to find literally a thousand or more tiny holes around the waterline when the discharge had exited! Apparently lightning does not always take the straightest path to the water, but rather has an affinity for the waterline.

The latest version of this NFPA 780 standard recognises this danger and, in a departure from the older versions, provides for multiple grounding terminals to provide the shortest path to the surrounding water surface. These ‘supplemental grounding electrodes’ conduct lightning current into the water in addition to that conducted by a main ground plate. The new standard provides for a continuous conducting loop outboard of crewed areas, wiring and electronics. Placing the loop conductor well above the waterline, outboard, and with grounding terminals below it retains the advantages of an equalization bus, whilst correcting for its weakness with side flashes having nowhere else otherwise to go.

Protection of electronic equipment by a hermetic system on larger yachts

So much electronic equipment on board a yacht struck by lightning is very susceptible to permanent damage. The only safe way to fully protect electronic equipment is to have it completely disconnected from all other circuits when thunder and lightning are nearby, and I still to this day do that as much as possible, but how practical is complete protection really?

A recent idea I had whilst discussing the problem with a 30m ketch owner may have some merit, and I call it a ‘hermetic system’, so suggesting that it is sealed from the outside world: If the most critical and/or sensitive electronic equipment can be enclosed within its own quite separate power and cabling set, separate from the rest of the boat’s electrical and electronic wiring, then it is possible that it could be saved in the event of a lightning strike. One way to do this would be to run all those systems required to be protected effectively off an Uninterruptable Power Supply (UPS), powered from the AC bus (via the generator), then down converted to the necessary 24/12VDC electronics supply. In the event of a lightning storm, all AC connections to the UPS and any signals, power or ground returns outside the hermetic system must be open circuited by large clearance contactors. The electronics contained within the hermetic system can still continue to operate, for a limited time (depending on the capacity of the UPS batteries) and further choices can be made about what to shut down within the hermetic system to extend the battery life, leaving for example just the absolute minimum electronics to continue to safely navigate e.g. Depth, GPS, Chartplotter. Very careful consideration must be given to cable runs.

The VHF antenna on the main mast may be protected by a surge arrestor from one of several suppliers e.g. www.nexteklightning.com. No guarantee is likely to the effectiveness of this as a protection device in all cases of lightning strike and the manufacturers should be consulted for further information.

I certainly now resort to the marvel of a GPS chart plotter on my mobile phone when there’s a nasty electrical storm about and I’m out at sea! References: –

1. Top 10 best lightning strikes (USA) by Pecos Hank, with rare photo of an upward streamer. 2. http://marinelightning.com/index_files/SFMechanism.gif for a graphic showing the formation of negative streamers 3. ABYC (US) technical report TP-4 “Lightning Protection”. 4. Nigel Calder – “Boatowner’s Mechanical and Electrical Manual: How to Maintain, Repair, and Improve Your Boat’s Essential Systems” 5. “Complexities of Marine Lightning Protection”, By Ron Brewer, EMC/ESD Consultant, April 2011 6. “A New Concept for Lightning Protection of Boats – Protect a Boat like a Building” Ewen M. Thomson, Ph.D.; published in the October 2007 edition of Exchange 7. National Fire Protection Association (US) document NFPA 780-2014 “Standard for the Installation of Lightning Protection Systems” – see especially chapter 8 ‘Protection for Water craft’. 8. “Evaluation of Rolling Sphere Method Using Leader Potential Concept – A Case Study” P.Y. Okyere, Ph.D & *George Eduful – Proceedings of The 2006 IJME – INTERTECH Conference

Feature article written by Andy Ridyard. Andy Ridyard has been a professional electrical and electronics engineer for more than 35 years and started SeaSystems in 2008. His business is dedicated to providing troubleshooting, repair and installation services to superyachts internationally, specialising in controls and instrumentation. He lives with his wife in Falmouth, UK, but works mostly in the Mediterranean. SeaSystems has fixed countless intractable problems with marine control systems, marine electronics, Programmable Logic Controllers (PLCs) and marine electrical systems. For more information visit SeaSystems.biz .

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Marine Lightning Protection

• Introduction
• Sideflashes
• The lightning system
• Collaboration
• Air terminals
• Grounding concepts
• Grounding guide
• Design & build
• Connections
• Grounding Strips
• Siedarc TM Electrodes

4.3.2.         Shielding

4.3.3.        grounding.

While it is straightforward to simulate the top three sides of a Faraday cage with down conductors, the bottom of the cage needs to be in the water to avoid sideflashes as noted above. In fact, if a long grounding electrode is immersed in the water directly below the conductor the risk of a sideflash from the bottom of the conductor is effectively eliminated, as shown in Figure 4-5 representing a strip-shaped immersed electrode . Since the vast majority of sideflashes propagate towards the water, the shapes of grounding electrodes are more important than the down conductors above the conductor.

Note that in both Figures 4-5 and 4-6 the potential of the conductor is close to that of the lightning protection system even though the two are not bonded. Thus the risk of a sideflash between the down conductor and the conductor is virtually eliminated.

5.     Theory for sideflash initiation

5.1. charge removed by lightning, 5.2. sideflash mechanism, 5.3.     quasi-static field model.

If we assume that the dimensions are much smaller than a wavelength, then both the current density and electric fields are quasi-static and electrostatic concepts can be applied. In this case the electric field at a particular point is proportional to the voltage, and, in particular,

where the constant of proportionality {E max /V}is a geometrical factor, that is, depends only on the shape and location of the fitting. Electrical breakdown occurs if E max (t) exceeds the critical field strength, about 10 7 V/m in air. It is useful to express this factor in terms of an equivalent distance, d eff ={E max /V} -1

In the case where time variations are slower than the relaxation times, the situation is ohmic so that the voltage v(t) is proportional to the current i(t). This corresponds to the usual interpretation for lightning grounding. Terms such as "ground resistance" and "step potential" imply this linear and in-phase relationship between voltage and current. Since the relaxation times in water are smaller than the characteristic time scales of most lightning processes, the exception being the rise time of subsequent strokes, it is a reasonable assumption when currents are flowing into the water. In this case ground resistance can be calculated for various geometries of grounding electrode. That is,

v(t)=R g i(t)

where R g is the ground resistance. See Thomson (1991) . Note however that these calculations do not assume that the current flow terminates on the water surface and hence underestimate the resistance. Also, since propagation phenomena in the water are ignored as well, voltage predictions are probably severely underestimated. In fact, since the wavelengths of electromagnetic waves in water are so much shorter than in air it is even questionable that we can assume a quasi-static model.

While it is difficult to estimate the absolute magnitude of the voltages and electric fields involved, the parameter d eff is very useful for predicting the relative likelihood of a fitting, or electrode, to initiate a sideflash relative to another. d eff can be generally interpreted as the minimum radius of curvature for a perpendicular fitting that is not close to the waterline. Fittings that are further from the lightning grounding electrode, closer to the water, and with smaller radii of curvature are the ones most likely to break down first. In the case of a boat in fresh water, even a lightning protection system with the more effective ground strip is likely to initiate sideflashes from almost any fitting that is not shielded by the strip. The two cases described in the next section illustrate these principles.

6.    Two case studies

6.1.     common features.

• The rigging was grounded to the keel ballast, the grounding area was well in excess of 1ft 2 , and yet sideflashes occurred.
• The sideflashes blew holes in the hull at the waterline.

6.1.1.        Current flow through grounded keel

Figure 6 ‑ 1 Lightning damage to grounded boat in fresh water

There are several interesting features in this case.

• The holes in the ballast, indicated that current had flowed out of the keel ballast, which had a much larger area than 1 ft 2 .
• The two sideflashes made holes at the waterline.Note that the waterline is the intersection of the hull's outer surface with the surface of the water.That is, the waterline forms an edge that provides a local electric field maximum conducive to discharge initiation.
• The origin of each sideflash was a chainplate at the lower end of a stay, a long narrow conductor that is oriented at right angles to the water surface. d eff for a stay is expected to be of the order of its radius, that is, very small compared to other nearby fittings.
• Both sideflashes connected through intermediate conductors that were electrically isolated from the lightning protection system.This demonstrates the occurrence of both internal and external sideflashes.

In order to provide for adequate protection in this case the following remedies would be useful:

• Additional grounding electrodes in the general vicinity of the backstay/organizer and forestay/water tank would provide alternative grounding paths for the discharge that formed from the forestay and backstay.
• Electrodes amidships would also be advisable, given that one of the sideflashes punctured the hull in this region.
• The optimum location for all grounding electrodes is at the waterline.
• A bonding connection between the lightning protection system and the aft organizer would equalize the potential between these and eliminate the risk of an internal sideflash.Note however that, in the absence of additional external lightning conductors and grounding electrodes, this bonding connection also increases the risk of an external sideflash.
• Potential equalization is also required for the water tank. However, for a plastic or fiberglass tank, bonding connections are impossible .Instead, a preferable technique would be to employ the concept of shielding by using external conductors and ground current injection as illustrated in Figure 4 ‑ 6 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000D0000005F00520065006600370039003500370036003100360032000000 .

6.1.2.         Current flow avoiding grounded ballast

Figure 6 ‑ 2 Lightning damage to grounded boat in fresh water

• There was no indication that current flowed out of the keel. The keel was painted but not encapsulated in fiberglass.
• The sources of the apparent sideflashes were the down conductors from the two sidestay chainplates.
• The holes once again were at the waterline.

7.     Implementation in a lightning protection system

7.1.     objectives.

• Layout of lightning conductors near the outer surface of the hull;
• Extensive bonding of conducting fittings to the lightning protection system;
• Incorporation of multiple grounding electrodes near conducting fittings that are susceptible to sideflashes;
• Optimization of grounding electrode design to maximize effective contact area with the water at the time of the peak lightning current.

7.2.     Sideflash hazards

Figure 7-1 Regions of high sideflash risk

In practice, a sailboat has many more conducting fittings near the waterline so that in practice the region of sideflash risk would encompass effectively the whole volume near and below the waterline. In a powerboat the problem is even more pervasive.

7.3.     Layout for lightning conductors and grounding electrodes

7.4.     utilization of siedarc tm electrodes.

• The charge removed by lightning resides on the surface of the water.
• A sideflash propagating in the air just above the water surface is limited only by the availability of the lightning charge.
• The calculation of ground resistance for an immersed grounding conductor is problematic.

The case studies in Section 6 demonstrated both the ineffectiveness of immersed grounding conductors and the tendencies for sideflashes to cause damage at the waterline, in agreement with these three conclusions.

Combining these theoretical and empirical considerations, we advocate multiple Sidearc TM electrodes distributed around the perimeter and just above the waterline to most effectively dissipate the lightning charge.

8.   Summary

As the interface between the water and the lightning protection system, the grounding system provides discharge paths for the lightning charge. The main function of the grounding system is to prevent sideflashes, both from conducting fittings to the water and between conducting fittings. In order to perform this function, multiple exit terminals are required and current flow into the water is maximized to limit the voltage of the lightning protection system. In addition, lightning conductors are interconnected to form an external grid that minimizes electric fields inside the boat. Layout of lightning conductors and grounding electrodes takes account of conducting fittings such as metal toe rails and handrails that can be used as part of the system, as well as those that are at high risk of forming sideflashes, and therefore need to be shielded or bypassed. The use of Siedarc TM electrodes facilitates grounding paths to be established from the lightning protection system to the surface charge on the water.

Yachting World

• Digital Edition

Expert sailing advice: How to handle a lightning strike on board

• August 21, 2019

Pip Hare shares advice from sailors who have experienced a lightning strike on how to avoid getting hit by an electrical storm

The 2015 Volvo Ocean Race encountered electrical storms. Credit: Brian Carlin / Team Vestas Wind

Lightning is the thing that scares me the most at sea. Having never experienced a lightning strike I think this is mostly a fear of the unknown, coupled with a sense of helplessness.

My lightning strategy has always been to sail in the opposite direction and hope for the best. The following is a combination of my own practice and observations from sailors who’ve experienced a lightning strike first-hand.

Avoiding lightning

Thunderstorms are created in conditions where there is great instability between the upper and the lower layers of the atmosphere. Typically, thunderstorms follow an extended period of warm, still weather , but lightning can also form along very active frontal systems – this tends to follow a sustained period of average pressure, with little gradient breeze when the new front moves in quickly.

Forecasters can predict where there will be increased potential for lightning to form, but not its actual occurrence or exact location.

Specialist forecast models such as the CAPE (convective available potential energy) and the LI (lifted index) show storm potential by highlighting areas of atmospheric instability.

CAPE and LI forecasts are available via specialist weather sites and CAPE GRIBs can be obtained through some providers. Satellite images can also be useful for spotting intense areas of cumulonimbus clouds.

If planning a sailing voyage in areas where lightning could be expected, include a CAPE forecast in your daily GRIB run.

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Flashes on the horizon

If you get caught out or have to sail through an area where electrical storms are expected, it’s important to prepare for all the weather a thunderstorm can dish out, not just lightning.

Thunder claps can be heard for around 25 miles, so if the sky on the other side of the horizon is alive with light but you can hear no noise then stay vigilant but don’t panic – the storm is still a way off. Keep moving.

Keep a 360° look-out: due to the immense height of thunderclouds they are pushed along by upper atmosphere wind, not the sea-level breeze. This makes it difficult to predict which way a cloud is moving, they can sneak up behind you while you are sailing upwind. The best way to track thunderclouds is using the radar or a hand-bearing compass.

Prepare for a squall: wind associated with thunderclouds can reach in excess of 40-90 knots in a matter of seconds, this will often be combined with torrential rain and drastically reduced visibility. If there’s lightning around it’s best to keep on-watch crew in the cockpit so make sure you reef early.

Preparing for a strike

Lightning can strike up to ten miles away from the cloud that generated it. Just because you are in the midst of a thunderstorm doesn’t mean you will get hit – I’ve spoken to two sailors who reported lightning striking the water next to their boat but not touching them.

Others that were struck reported varying damage to electrical equipment and none experienced structural damage or fire. Here are some of their recommendations:

• Unplug all masthead units, including wind instruments and VHF antennas and ensure ends of leads are kept apart to avoid arcing.
• As the storm gets closer turn off all electronics – modern kit has increasingly efficient internal protection, but manufacturers still advise turning it off.
• Take a fix and plot it on a paper chart. Update your log using dead reckoning.
• Avoid touching metal around the boat, such as shrouds and guardrails.
• A nearby strike will be blindingly bright. Sit in the cockpit until your night vision returns.
• Expect masthead units, VHF antennas and lights to be destroyed, so make sure you carry a good quality spare VHF antenna.
• Fluxgate compasses can lose calibration following a strike. Check all electronic compass readings with a handheld compass.

Maximising protection

By providing a direct route ‘to ground’ down which the lightning may conduct you may be able to minimise damage.

Among my small sample of interviewees, only one had a lightning protection system: this was a sloop with a deck-stepped mast on which the chainplates were bonded to the keel bolts. The masthead unit on this boat was still totally destroyed by the strike but the remaining electronics suffered no ill effects. The same sailor had experienced a strike two years earlier with no extra protection installed – in that instance all electronics were destroyed.

The remaining sailors were all in boats of less than ten years old and reported varying degrees of damage to electronics and 100% destruction of masthead units.

The simplest protection system is bonding an aluminium mast to the keel bolts. On a keel-stepped mast this is easily done as the mast heel and keel bolts are close to each other. For deck-stepped masts this can be achieved by running an adequately sized cable through the deck head and down a bulkhead or supporting pillar.

Most modern boats have the mast bonded to the keel by manufacturers – if you’re not sure lift the soleboards to check. Masts made of less conductive materials such as carbon would require a conductor cable as well.

Air terminals at least six inches higher than any antennas at the top of your mast may save your masthead units. There is also considerable debate over the need for dedicated grounding plates – this appears to be more relevant to older boats as none of my interviewees suffered ill effects through grounding to the keel bolts.

Faraday cage

There is a theory that the oven on a yacht can act as a Faraday cage, protecting anything inside it from the effects of electrostatic discharge (ESD). Handheld or portable electronics can be temporarily placed inside a metal oven to protect them during a storm.

I have no conclusive evidence this works, but I’ve always done it, reckoning it can’t do any harm – just remember to take them out before dinner!

• Practical Boat Owner
• Digital edition

Make a grounding system to protect your boat from lightning strikes

• March 5, 2021

Metallurgist Vyv Cox explains how a heavy conductor can keep you safe at sea during lightning storms

A surprising amount of research has been carried out into lightning strikes on yachts and boats, much of it in Florida but some in New Zealand, Australia and other countries. The findings are somewhat confusing when it comes to the layout of protection.

To summarise, the optimum protection according to all authorities is provided by a heavy conductor, preferably copper of at least 21 sq.mm. running from 15cm above the masthead and all antennae in as straight a line as possible to an underwater plate beneath the mast foot (see Fig 1 ). This should be copper, bronze or Monel, not sintered and not embedded into the yacht’s hull, as electricity prefers to exit via an edge.

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This arrangement creates what is known as a ‘cone of protection’ within which people are relatively safe provided they are below deck, sitting as high above the waterline as possible and well away from the mast (see Fig 2).

The American approach is similar but greater attention is paid to the possibility of side flashes, which may be particularly damaging to electronics and may even blow holes in the hull. This is the reason for the USA preference for electrically bonding all underwater components, such as seacocks, engine, drive and rudder. The cable used is of considerably heavier gauge than is needed for purely galvanic purposes. It is believed that this practice forms a cage-like network of conductors, helping to protect anything within it.

Further problems arise in the case of secondary paths from the main, vertical, path of the current, where the electricity can follow unpredictable routes to the sea, resulting in serious damage and risk to life. Again, bonding helps to reduce the likelihood of secondary paths but may have an adverse effect on corrosion.

Grounding system to protect against lightning

A grounding system is designed to provide a very low resistance path to the ground. The air terminal should be made of copper rod of between 10mm and 19mm diameter, installed at least 150mm above all other objects on the boat. On a yacht, this is typically at the top of the mast. On a powerboat, a mast structure of some sort is required.

The down conductor cable provides a low-impedance path between the air terminal and the external grounding plate. An aluminium mast is usually sufficient to facilitate the necessary lightning flow, but should be connected by the cable at its base to an external grounding plate in order to complete the circuit. Non-aluminium masts (eg. carbon fibre and wood) need a conductor.

The external grounding plate should be located where it’s never out of direct contact with the water, and should be made of either copper, bronze or Monel (a predominantly nickel and copper alloy). A long strip is more effective than a square plate.

• Find out what marine surveyor Ben-Sutcliffe Davies has to say about lightning strikes

Some more useful websites on lightning

The National Agricultural Safety Database (NASD) Discover Boating Club Marine

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MARINE LIGHTNING PROTECTION: Getting Z-Z-Z-Zapped on a Sailboat

I have to admit I don’t normally think about this too much. As is true of many sailors I suspect, I have subscribed to the philosophy that lightning and its effects are so random and poorly understood that you can get royally screwed no matter what you try to do about it. Which is a great predicate, of course, to going into denial and doing nothing at all. But the death in Florida last summer of Noah Cullen , a most promising young man who presumably was killed in a lightning strike while out singlehanding on his pocket cruiser, got me pondering this in a more deliberate manner. On doing some research, I found there are some hard facts out there that are well worth knowing.

Much of what we tend to learn about lightning is anecdotal, which mostly serves to make it seem more mysterious. I, for example, have never been struck by lightning, but I did once cut through some severe thunder squalls in the Gulf Stream in a grounded fiberglass boat and saw a bolt of lightning the size of a large tree trunk flash straight into the water just a few yards behind us. I can’t begin to tell you why it didn’t hit our nice 55-foot aluminum mast, and ever since then I’ve believed a strike is pretty much an act of God. It’s either going to get you, or not, and there’s nothing you can really do about it.

I have met a number of sailors who have been struck by lightning, mostly in grounded boats, and in every case they told me they lost all their electronics. So I have also always assumed there is nothing you can really do to protect installed electronics from a lightning strike.

But you should forget all the anecdotes you ever heard, at least temporarily, and think about the following:

Likelihood of a strike: It’s probably much higher than you like to think. One source states that a sailboat with a 50-foot mast will on average be struck once every 11.2 years. According to insurance data, the general average for all boats is about 1.2 strikes per 1,000 boats each year.  The average bill for damage is around $20,000. Most strikes are on sailboats (4 strikes per 1,000 sailboats each year). And these are likely lowball numbers, as it seems many lightning-strike victims are not insured or do not report the strikes to their insurers. According to one independent survey, unreported strikes could be as high as 50 percent of the total.

Location is also a big factor. Some areas, including very popular cruising grounds like Florida or Chesapeake Bay, are much more lightning-prone than others, and you are obviously much more likely to get struck when sailing within them. The overall average for reported lightning strikes on boats in Florida, for example, is 3.3 strikes per 1,000 boats each year, nearly three times the national average.

Map showing lightning strike probabilities around the world. The higher the number, the higher the probability

Interestingly, catamarans overall apparently are struck twice as often as monohulls. Could this be because they are effectively twice as much boat???

Preventing a strike: It really isn’t possible. There is no technology that can positively keep your boat from being hit. There’s seems to be little evidence, for example, that those silly little masthead bottle brushes some people put up are good for anything.

Spectacular image of a sailboat getting hit in Rushcutter’s Bay in Sydney Harbor, Australia, with inset images showing damage to the mast. Lots of other targets with masts around, so why did the bolt hit this one boat?

Limiting damage: This is where the action is. To paraphrase one writer: it is a fallacy to think in terms of “lightning protection.” What you want is “lightning control.” Which definitely means grounding your boat! An ungrounded boat is much more likely to suffer potentially disastrous damage when struck (i.e., holes in the hull, dead crew, etc.). A boat in fresh water is also much more vulnerable, because fresh water doesn’t conduct electricity as well as salt water. An ungrounded boat in fresh water is most vulnerable of all. If you’re on one of these during a strike, you may as well just forget about it and put a cap in your head.

Typical exit damage around an anchor well drain on a fiberglass boat. Hull damage just above the waterline is not at all unusual

Grounding your boat: The old school notion of leading a big copper strip from the base of your mast in a straight line to a single grounding plate on your hull is the process of being discarded in favor of a more sophisticated technique that connects the mast as primary conductor to a network of dissipating electrodes installed just above a boat’s waterline, the idea being in effect to make all of the boat’s hull something like a Faraday cage, so that the equipment and people within will be safer.

Example of a more modern grounding system

Note (I was particularly gratified to learn this): a metal hull is indeed a great ground, and the fact that it is painted, or coated in epoxy, or whatever, doesn’t change this. But you can still suffer significant damage on a metal boat!

Bonding: You and the gear on your boat are more likely to survive a strike without damage if the major bits of metal on your boat are bonded to the grounding system. This reduces the likelihood of dangerous side flashes. (It does, however, create complications with respect to the potential for galvanic corrosion on a boat.)

Saving electronics: First of all, stowing handheld electronics (or any disconnected electronics) in your oven will protect them during a strike. Just remember to take them out again before using the oven!

More importantly, you can protect installed electronics using various individual surge protectors, fancy spiral wiring, and other techniques I’m not going to pretend to understand, much less explain. See the sources below for more details.

Your personal safety: This should be most important, right? You want to stay off the helm if possible, stay below, stay dry, and don’t touch any big pieces of metal. All of which are easier said than done when you’re in the middle of a big squall! It would seem the most prudent tactic is severely reduce sail, or take it all down, pop the boat on autopilot, and get below well in advance of and after a thunderstorm.

Lightning and Sailboats : Academic paper published by Ewen M. Thomson, currently recognized as the most well-informed go-to guy on this subject.

Marine Lightning Protection : Website for a business run by Ewen Thomson (see above), who is a pioneer in modern cage-style boat-grounding techniques. Thomson will ground and bond your boat for you, if you like, but there’s also lots of useful raw info in here.

Lightning Survey Results : Discussion re results of a small independent online lightning-strike survey conducted by a cruiser who owns a power-cat named Domino . Very informative.

Considerations for Lightning Protection : Conclusions reached post-survey by the owner of Domino , referenced above.

Lessons in Lightning : Ocean Navigator article by a cruiser in an aluminum boat who was struck by lightning in the Baltic. Of particular interest to those (like myself) who own aluminum boats.

There are lots of other resources out there, but these four links are a very good place to start. You’ll find many other valuable sources just by reading through these articles and following the links within.

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STORM PORN: Casco Bay Thunder Squall

We were hit by lightning in a fast moving front off Newfoundland many years ago (before gps). All the electronics were fried! The binnacle must have been demagnetized as it hopelessly spun in circles, giving us only a hand sighting compass to steer by. The smell of burned wire insulation in boat was overpowering. Luckily this is a rare occurrence and for the most part just bad luck!

@Robert: Interesting. In Bermuda once I met a tall ship, steel hull, that had been struck by lightning, and as a result the whole ship was magnetized. Which also kept their compasses from working properly. They were on their way to Norfolk, Virginia, to get degaussed.

I feel obligated to take issue with a fair bit of what’s been said above. Without writing a textbook, the following is best seen as “almost correct”. If you consider that the sky has a positive electrical charge and the sea a negative charge, grounding the boat and the mast gives them a negative charge. Hence as far as the lightning is concerned, the bonded mast raised the local sea level to mast top height. Lightning will tend to bridge the narrowest gap with the greatest electrical charge difference – so by grounding boat and mast, you have made them MORE vulnerable to lightning strikes, not less. In other words, NOT grounding the boat and mast will REDUCE your chances of being struck.

Tying an earth system into the keel bolts is not likely to result in loss of the keel, but it sure does constitute trying your best to do so. If the bolts are electrically weak they may act as a fuse and “blow” during a strike.

Making a Faraday shield form shown above does help mitigate the effects of the strike compared to a simple bonding of the mast to the keel in many situations, but it’s over-rated. In a big strike, lightning will try to follow a straight path and the energy contained in such a strike is often too great for a simple system to be effective. And it needs to be understood that either method makes the strike a whole lot more likely to occur.

A grounded mast does offer a degree of protection to a non-bonded electrical system in the boat underneath. There is what’s termed a “cone of protection” extending downwards at 30 degrees from the top of the mast. This is the standard system used in telecommunications.

The best protection you can have is to park your ungrounded wooden boat with a wooden mast and an electrical system isolated from the sea, right next to a grounded metal boat with a big aluminium mast. In the photo above depicting the Sydney harbour yacht being struck, the question was posed “why did the bolt hit this one?” The answer is that it was best grounded boat in that area.

@Bryan Tuffnell while part of what you say is true that a grounded boat is more likely to be struck the catch is that it will do less damage if struck where as a boat not grounded is less likely to be struck if it ever is you will have significantly more damage

Maybe, but quite likely not. The only way to offer lightning protection is to place a grounded lightning target above the mast, but electrically isolated from the mast and every other part of the boat. The grounding is completely independent of the mast, rigging, interior, electrical system, and above waterline areas of the hull. The idea is that this attracts the lightning and provides a low impedance path to ground, without drawing the charge into any part of the boat or its contents. Using this strategy one does not ground the mast, hull, rigging, etc. This is the only strategy to apply if one insists on lightning protection.

the sky has a positive electrical charge and the sea a negative charge

Its the other way round. When polarity builds up the negative charge is at the cloud base, and the positive at the sea surface. [quote=Bryan TuffnellNOT grounding the boat and mast will REDUCE your chances of being struck[/quote] Wrong – the enormous voltage actually doesn’t care if you’re grounded or not. Given the fact that the boats surface will always be wet or moist in some way it is “grounding” enough to raise the sea level polarity up to the mast top. The only thing proper grounding does is trying to guide the current of a charge in a way that does the least harm.

Not necessarily in the first case, and generally not true in the second… the polarity of lightning is variable, and there are countless examples of nearby strikes to ungrounded boats. Obviously if lightning didn’t care of you were grounded or not, lightning conductors wouldn’t work.

As far as doing the least harm goes, grounding the mast is about the worst thing you can do, particularly if you have grounded electrical items onboard.

Our boat (20′ cruiser) has no grounding system. Is it foolish to think that the method where a set of jumper cables is attached to mast and other end dropped overboard, might be a good emergency strategy if caught in elec storm?

what a topic indeed. to protect or not to protect, that is the question. simply do you use a brush type or spike type diffuser on your mast, do you protect for side strikes, or stay central with mast bonding.. im trying to find an answer like us all and so far , the answers all differ..

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Modern Lightning Protection On Recreational Watercraft

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While you can't prevent a strike, there's a lot you can do to mitigate — or even prevent — damage.

A thunderstorm passing over a marina has the potential to cause expensive damage.

The recent advances in electrical and electronic systems have revolutionized recreational boating. Vessel operations have been simplified and the boating experience enhanced due to the integration of electronics into almost every onboard system, from navigation and communications to propulsion and maneuvering. Complex engine electronics known by various names including Engine Control Unit (ECU) and Engine Control Module (ECM) have increased performance and reduced emissions on modern engines. However, these advances have come at a cost. Many 21st-century boaters depend on electronic systems to navigate and maneuver their boats, and many modern engines will not function if their electronics are compromised. That makes modern mariners and their boats vulnerable to a lightning strike that damages these now mission-critical systems, potentially leaving the boat dead in the water without navigation or communications equipment.

Unfortunately, sensitive electronics on boats have become increasingly vulnerable to lightning strikes, yet lightning-protection systems have not kept pace. It's not that there haven't been significant advances in lightning science since Benjamin Franklin developed his theories on how to protect barns and livestock. The National Fire Protection Association, Underwriters Laboratories, and industries which are significantly at risk from lightning, such as telecommunications, wind generation, aviation, and fuel, have achieved consensus on the science of lightning protection and have embraced new protocols and practices. But the recreational boating industry has been slow to adapt those changes to the marine environment. There are at least three reasons for that.

There is no evidence from independent laboratories that these fuzzy lightning dissipators prevent strikes.

First, corrosion and motion on board boats, as well as limitations with respect to weight, space, and geometry, make lightning protection more challenging than in shoreside installations. Second, the mandate of the standards body for the industry, the American Boat & Yacht Council (ABYC), focuses on protecting life; protecting equipment has been a lower priority. Third, there has been strong disagreement between professionals about the best way to mitigate damage in a lightning strike and precious little data to support one point of view over another. The sometimes-raucous debate surrounding certain unproven lightning- protection devices and such theories as "fuzzy" lightning dissipation terminals and early-streamer emission terminals, as well as unorthodox placement of grounding terminals (a.k.a. grounding plates), have sharply divided the recreational boating technical community, all of which makes consensus on lightning protection difficult, if not impossible.

This lack of guidance is frustrating for those with boats at risk. While a runabout in Portland, Oregon, or a daysailer in Portland, Maine, may have little risk of lightning damage (see " Striking Lightning Facts "), larger vessels (particularly sailboats) in such lightning-prone areas as the Chesapeake Bay or Florida absolutely should be protected using the best technology available. Any marine-insurance adjuster can attest that the potential for loss on these vessels can be great. The National Fire Protection Association made some fundamental changes to the watercraft chapter of NFPA 780: Standard for the Installation of Lightning Protection Systems in 2008 that incorporate the thinking that has become accepted in other industries. While the recommendations in NFPA 780 have yet to be embraced by the recreational boating industry as a whole, understanding what it says — and why — may assist you in developing a lightning-protection plan for your boat.

Lightning 101

The simplest way to think of a lightning strike would be as a short circuit between the cloud and the earth. The earth and an active thundercloud have either a positive or a negative polarity with respect to each other, just like battery connections that can arc if they are not separated by a long enough air gap. Whether the positive charge is in the cloud or on the water may have great importance to a physicist, but matters little to the cow in the barn or the VHF radio antenna on the mast.

The important point is that the earth (or in our case, the water) contains an unlimited supply of positive and negative charges; it is the thundercloud that induces the charge concentration in the water. For example, if a large concentration of negative charge coalesces in a storm cloud over the ocean, a large concentration of positive charge is drawn to the very top surface of the water directly beneath it. (Opposites attract.) Since air is a good insulator, no electricity will flow between the cloud and the water unless the airborne charge loses altitude, moves close enough to the surface of the water, and the lightning jumps the gap. If an electrically conductive material, such as an aluminum tuna tower or mast, stainless steel rigging, or a long vertical copper wire, comes between the cloud and the water, then the gap that must be jumped becomes shorter. The boat short circuits the voltage, much like a wrench across battery terminals.

Because boats are built from electrically conductive components installed between the water and the areas aloft (masts, rigging, antennas, towers, support structures, electrical wiring), a lightning strike is inevitable if an active thundercloud containing electrical charges passes overhead at a low enough altitude. How much damage the lightning strike does to the boat depends upon how easily the electrical energy from the strike can find its way through the boat to ground. There will be a lot less damage if the discharge is contained in a well-designed lightning-protection system than if it takes a detour through the ship's wiring and sensitive electronics on its way out of the boat.

This is a basic concept that surprises many boaters: A lightning-protection system is not designed to prevent a lightning strike, but rather to provide a safe discharge path for the lightning. This is the only viable solution for lightning protection (short of going back to wooden ships, kerosene lamps, and sextants). The technology to prevent lightning strikes does not yet exist.

Still, there are devices out there claiming to do just that. Lightning dissipaters (LDs) look like metal bottle brushes or frayed paint brushes and are installed on the top of the mast. The hypothesis is that the numerous conductive points on the LDs safely dissipate accumulated charges so the lightning strike will not occur. As far as I am aware, not a single independent testing laboratory has confirmed the effectiveness of lightning dissipaters as lightning preventers.

Early-streamer emission (ESE) terminals have also gained traction in some circles. Fancy lightning rods often shaped like a torpedo that usually come with electronic circuitry, these are supposed to attract lightning better than a standard lightning rod (also called an air terminal), to ensure that the lightning strikes the grounding path rather than what is being protected. Once again, I am not aware of any independent studies validating the effectiveness of these devices.

Lightning-protection systems actually function by acting as the "best" short circuit between the cloud and the water, one designed to lead the lightning harmlessly to ground. The system accomplishes this in two ways: by attracting lightning away from more destructive pathways between cloud and ground, and by sending the charge around, instead of through, what it is protecting.

The first concept has traditionally been known as the "cone of protection" or the area protected by an air terminal from a strike. Traditionally, the cone of protection has been thought to include a circle centered on the base of the air terminal whose radius equals the height of the terminal and to extend from the top of the air terminal to the ground at a 45 degree angle. In fact, the length of the final jump that lightning takes before striking the air terminal is about 30 meters. Recent research suggests that the actual area protected can be defined by an imaginary sphere with this radius that is "rolled" up to the air terminal. All objects inside the imaginary sphere will not be protected by the air terminal, which means the area protected often differs in size and shape from the cone of protection model. Modern lightning protection for airports and power plants use the rolling sphere method and place air terminals so that the areas of protection overlap and include any sensitive equipment that would be damaged by a strike.

The second concept will be familiar to many as the Faraday cage. As early as 1836, Michael Faraday discovered that objects surrounded by metal were protected from lightning (explaining why we are safe from lightning while in our cars). Many old-school sailors have used Faraday's discovery to good purpose when they placed sensitive electronics in the oven during a lightning storm (with the oven off, of course.) This practice can be significantly updated by placing sensitive electronics in the microwave oven!

21st Century Lightning Protection

Benjamin Franklin pioneered lightning protection in 1749 with the invention of the lightning rod, and, when it comes to recreational boats, until recently, little has changed. Under his model, the lightning is attracted to the lightning rod (air terminal), which then passes the lightning current harmlessly to a submerged metaevent secondary flashes from these metal structures.

Air Terminals are shown in green; grounding plates with down, side flash, and equalization conductors in yellow; loop conductors in red; and catenary conductors in blue.

NFPA 780 draws much from the old-school system while incorporating improvements based on the modern understanding of lighting protection. While solutions will vary depending on the boat, let's talk about the basics.

Air terminals (lightning rod or Franklin rod) should be installed at the highest points of masts, towers, etc. On a sailboat a single air terminal could be bolted to the mast; on a sportfish it could be bolted to the tower and made to look like an antenna. This should be higher than anything you are trying to protect from a lightning strike, such as a VHF antenna.

A heavy electrical conductor should be connected from each air terminal directly down to a grounding point on the hull. In the case of a sailboat's mast, aluminum is a good conductor, so no separate wiring run needs to be installed. (Note that the wiring inside of the mast will be protected due to the Faraday effect.) An aluminum tower will work the same way on a sportfish so long as the legs are connected to an adequate grounding plate. Where no aluminum structure exists to act as a down conductor, a 4 AWG wire or larger should be run from the air terminal to the grounding plate in as straight a run as possible and well separated from other wiring.

The grounding point should be a corrosion-resistant metal plate installed on the exterior of the hull below the waterline. The plate should be at least one square foot in size and at least 3/16 of an inch thick. Research shows that most of the electrical discharge occurs along the edges, so a long, narrow plate, especially one with grooves cut in it, will be most effective at dispersing the charge. A new major point of contention is where to install the grounding plate, or plates. Some research indicates that a location at or near the waterline is by far the most effective solution. On a sailboat, the lead keel can be used as the grounding plate if the keel is not fiberglass-encapsulated or covered in fairing. If the mast is solidly keel stepped, there would be no need for a separate conductor from the mast to the keel. Metal rudders or propeller struts are also acceptable as grounding plates.

Protecting Electronics

Surge-protective devices (SPD) or transient voltage surge suppressors (TVSS) should be installed on all equipment that's mission critical, expensive, difficult to replace, and/or prone to lightning damage. Examples include the ECU/ECM, alarm systems, chartplotters, and instruments.

A bank of TVSSs protecting sensitive electronics.

TVSSs are the most exciting development in the field of lightning protection. These semiconductor devices provide protection by suppressing lightning-related voltage spikes. They are widely used in the telecommunications, wind generation, and avionics industries.

TVSSs are connected across the input terminals supplying voltage to a piece of equipment; they can be thought of as fuses that react to voltage instead of current. The TVSS is an open circuit as long as the supply voltage feeding the equipment is in the normal range. However, if a lightning strike causes a momentary voltage spike and puts, say 1,000 volts on a 120-volt device, the TVSS will "clamp" or short circuit 880 volts and convert it to heat. The excessive heat could, and probably would, damage the TVSS; but destroying a $250 surge arrestor to protect a $5,000 engine controller is good engineering.

Grounding plates should be long and narrow with groves cut into them to disperse the charge more efficiently.

Voltage surge protection would be prudent for engine controls, navigation systems, steering systems, and shorepower systems. TVSSs come in many voltage ratings, energy ratings, response times, and so on. Some are designed to protect whole distribution systems, while others are suitable for individual equipment protection only. A well-designed system includes cascaded protection, with extra protection on mission-critical and lightning-prone equipment, such as main engines and shorepower systems. The key to a reliable and cost-effective system is to ensure that appropriately rated devices are specified and properly installed. The best TVSS in the world will be ineffective if it is not connected properly.

Despite the best technology, there can still be challenges with an NFPA 780-based system, particularly when the system is improperly or only partially installed. For example, if the air terminal is installed lower than an adjacent antenna, it will not protect the antenna; in that case, the antenna cable carries the lightning current. Also, if the down conductor is connected to the bonding system rather than directly to a dedicated grounding terminal (ground plate), the lightning strike can energize the entire bonding system before discharging into the water. Another common mistake is to secure the lightning down conductor to other wiring. The high current from a strike through the down conductor can result in voltage surges in these adjacent wires, leading to additional damage in equipment that would otherwise be completely unaffected by the lightning strike.

In Conclusion

The recent revolution in marine electronics demands an evolution of our thinking on marine lightning-protection; equipment protection should be an important aspect of any modern lightning protection system. The knowledge and resources to safely transform this change in thinking into reality are readily available, both from the NFPA and industries also at risk from lightning. However, there are unique challenges on pleasure craft that are not addressed by others. These must be solved by sharing the experiences of lightning-protection systems and their effectiveness across the industry.

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James Coté

Contributor, BoatUS Magazine

James Coté is an electrical engineer, ABYC Master Technician, Fire Investigator and Marine Investigator. He operates a marine electric and corrosion control consulting firm located in Florida. For more information, go to: cotemarine.net

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A Quick Comprehensive Guide to Lightning Protection for Boats

Understanding lightning mitigation for boats, techniques to lessen the impact of a lightning strike, adopting standardized lightning protection for boats, key components of a boat's lightning protection system: wiring, air, and ground terminals.

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Should I ground my mast to the keel?

• Thread starter msmalter
• Start date Mar 8, 2014
• Featured Contributors
• Musings With Maine Sail

I have a Catalina 28 that is not bonded. I've read the ABYC recommendation as well as many other articles, and believe that bonding "may" increase the chance of getting hit by lightning, but will reduce the damage to the hull if it does get hit. I was planning to ground the mast to a keel bolt this spring using at least #4 wire (I've seen recommendation for up to 2/0). Some on the Catalina Forum suggest that I should not do this. Others say if I do it I need to ground all the chainplates also using #6 wire. I'm concerned that the #6 wire willl be next to the hull and could cause a sideflash through the hull. What do you recommend? (Do nothing, just mast, or everything)? What size wire? Does it make a difference if the boat is in fresh or salt water? (I'm in fresh) Mike Smalter  

There is lots of new thought on lightning grounding. MY opinion is lightning clouds induce a charge on the SURFACE of the water (<1/4" deep). The keel is deeper (and at a higher potential )than that so grounding the mast to the keel just brings lightning into the boat with nowhere to go except out the side of the hull. The electrical potential of the mast to keel wire has a very odd (for a wire) voltage distribution in this situation. High at the mast end, zero at the level of the water surface and higher (not as high as the mast but higher then the water surface) so the lightning has not reason to continue to the keel and tries to find the shortest route to the water surface, in this case it is (as the insurance folks will tell you) through some metal part near the hull and at the water surface level. Better to leave the keel disconnected and ground the shrouds and stays over the gunnel and down to the water surface and not bring the stuff into the cabin at all. You are going to find there is NO consensus on this topic so I'd take my info from the building industry which NEVER runs the lightning arresting wires into an occupied space and has not had much of a problem with frying stuff in the last 100 years or so. The only (IMHO) difference between a boat and a building is the actual "grounding rod" and the fact that earth is not as good a conductor as sea water.  

Stu Jackson

Read this and then make up your own mind. http://www.westmarine.com/WestAdvisor/Marine-Grounding-Systems Good luck.  

Ask the boat manufacturer the reason for which they do not bond the boats at the factory. If their answer is, as per recommendations of their attorneys you may take that to the Bank. The reality is that no one knows and opinions keep changing. Some seem to think that bonding not only increases the odds of getting a strike but also the severity of the strike. The awesome power in a lightning strike means it will go where it will go and not necessarily where we may try to steer it to. There is actual data that indicates that more strikes are recorded in boats near land than those at sea. Is that due to some interaction with land or just because there may be more boats docked than at sea at any given time. The legendary cone of protection afforded by the mast seems to work but then it could be just so by mere accident. I guess it just boils down to those that feel the need to be proactive will be happier if the bond and the rest of us will spare the time and effort for something else. There are two positive observations ; the risk to life and limb is minimal based actual count of casualties and a good insurance coverage will help mitigate equipment losses.  

If side flashes are the threat that Bill suggests (and it makes sense), it would seem pretty easy when at anchor or dock to clamp a piece of lifeline wire to a shroud and drop it in the water. Even better, attach a large copper bolt to the wire at the water surface. I've seen a short length of chain used but copper with sharp edges would seem a better dissipator Why not?  

Everything you ever wanted to know about sailboats and lightning can be found here: http://edis.ifas.ufl.edu/sg071 Produced by the University of Florida as part of NOAA's Sea Grant program. Great read for those wanting to know more about how lightning strikes form and move through a sailboat and what can be done to prevent substantial damage and injury to crew. Cheers, Brad PS: My H23 has, from the factory, a ground wire running from the base of the mast, down through the cabin and attached to a keel bolt.  

I just use car jumper cables. One end clamped to each side shroud, and then toss in the water. Nothing yet, knock on wood. When not being sailed, my boat sits on an elevated lift, on wooden slats covered with old carpet, so this would be the only contact with the water and hopefully give any lightening strike the "Path of least resistance". 1.21 gigawatts, Holy Crap Batman!  

SailingHarry

Every time the issue comes up, you hear the "some sort of wire over the side" argument. Seriously? You folks are sailing along, a thunder storm is coming up, you are working in a reef, and you have somebody clipping jumper cables onto a shroud and throwing it overboard? Or tie a chain around the mast and drag that over the waterway into the water? While making 6+ knots in a heavy sea? I just can't get my mind around that. Or, worse yet, you're going to make a connection with a giant alligator clip on a high resistance stainless steel shroud? While the commercial building industry does use a perimeter lightning grid with outside down-comers, they have no issues with how to get that to "ground" and it is as much a matter of convenience than anything. ABYC recommends a heavy grounding system (rig and mast) with a clear set of rules on how to do it. Most if not all boat builders follow that guidance. I'd be really leery about coming up with my own (or some other non-study based idea from someone else who has no engineering/electrical/study/lab basis). But as someone else mentioned, this is a contentious issue with about 1000 different opinions. So anything you do will meet with at least one approval! Back to the OP. I'd get the biggest wire I could, bond it to the mast as best I could, run as nearly vertical as I can, to the biggest keel bolt I can find. I'm about to upgrade my Sabre 34 mast ground from #10 (factory in 1979) to #1 (it's what I happened to have on hand) and I think that's a big improvement. The shrouds will still be #10 bonding -- hey, you can't do everything! Harry  

Thanks, Maine. There's just no substitute for real-world data and experience. I was toying with the idea of removing the bonding on my boat because it can make things worse in an electrically hot marina but now you've given me something to think about. We don't get much lightning here in the great PNW, but hopefully we'll someday be taking the boat to where it's more of a threat ;o).  

So MS Why do you think the lightning has a propensity for leaving the hull in some location other than the well bonded keel? I've been paying attention to this for years and it seems that lightning generally exits near the water line more often than not.  

Maine Sail said: I personally go well beyond ABYC standards. Our spar is bonded to the keel via 2/0 wire and these connections are kept clean and coated with terminal grease.. Click to expand

What have been you experience with encapsulated keels? Does the glass around the keel just blow off? Click to expand

Bill Roosa said: So MS Why do you think the lightning has a propensity for leaving the hull in some location other than the well bonded keel? I've been paying attention to this for years and it seems that lightning generally exits near the water line more often than not. Click to expand

Lightning Plate Material? MS, What would be the best material to make a ground plate for my encapsulated ballast full keel boat (Cabo Rico 38)? I've read that silicon bronze would be best, but I can't find a supplier of flat stock. Onlinemetals.com has aluminum bronze in stock and in the right sizes, but I'm not sure about saltwater corrosion with that material. They also have copper plate and flat bar stock, but again would the corrosion be a problem. Plan is to make 2 of 3/8" x 6" x 18" plates and install them on either side of the the keel just above the ballast cap. Connect to mast step with #2AWG. Also connect forstays and shrouds to the same plates with #4AWG. As a side note, I've looked at all the boats on the hard at my marina and two others, and I have never seen a boat with a ground plate attached to the hull of an encapsulated ballast boat. I wonder why? I have seen sintered bronze plates, but not sure if they are for lightning or a counterpoise. Another question: Should the Lightning ground be electrically seperate / isolated from the bonding circuits and DC ground? My bronze thru-hulls are bonded to DC ground and to 2 hull zinc anodes.  

SaltyHog said: MS, What would be the best material to make a ground plate for my encapsulated ballast full keel boat (Cabo Rico 38)? I've read that silicon bronze would be best, but I can't find a supplier of flat stock. Onlinemetals.com has aluminum bronze in stock and in the right sizes, but I'm not sure about saltwater corrosion with that material. They also have copper plate and flat bar stock, but again would the corrosion be a problem. Plan is to make 2 of 3/8" x 6" x 18" plates and install them on either side of the the keel just above the ballast cap. Connect to mast step with #2AWG. Also connect forstays and shrouds to the same plates with #4AWG. As a side note, I've looked at all the boats on the hard at my marina and two others, and I have never seen a boat with a ground plate attached to the hull of an encapsulated ballast boat. I wonder why? I have seen sintered bronze plates, but not sure if they are for lightning or a counterpoise. Another question: Should the Lightning ground be electrically seperate / isolated from the bonding circuits and DC ground? My bronze thru-hulls are bonded to DC ground and to 2 hull zinc anodes. Click to expand

brazenarticle

Hello MaineSail - If I may get back the the original question ( I also have a Catalina 28) what is best bet to get some level of protection? The mast is deck stepped on a stainless plate, I'm assuming fiberglass between that and the top plate of the compression post, and guessing there is no clean electrical connection other than wires in the mast. Would a #2 wire from keel bolt to compression post also need a jumper between post and mast? Attaching a longer directly will have to wait until I pull the mast for maintenance. How about the chainplates? Do they need to be connected to the keel bolts too? One last thing - what happens, what should I do if I am on the boat in a severe electric storm (common enough scenario on the Chesapeake). Is it just a numbers game that many more boats get hit but I have yet to hear of sailors struck? How long can we count on lightning bolts going for golfers more often than sailors?  

I think I'm going to stir this stew a bit more to get some clarification. Below is a plan I came up with after reading Calder's book and several lightning/bonding threads and I'd like some input/feedback. Page 233 of Calders book has a diagram where all the negatives/grounds/bonds (incl. lightning) go to a grounding bus, which is then connected to an "immersed ground plate or strip". However, another paragraph describes a separate lightning grounding system with external plate and no connection to common ground bus A. separate grounding system for lightning ground; cables straight/short as possible B. AC ground, DC negative, & bonding terminate at common ground, which has its own immersed plate External lightning ground strip (1/4" x 1.5" x ~120", I'm in brackish water) Through bolted about every 2 or 3 feet, wherever I can reach and get to if hole forms I have an isolation transformer 1. mast (2/0 wire), shrouds, stays connected (biggest I can manage up to 2/0) as straight as possible to external grounding strip through bolts. 2. Aluminum fuel tank (and deck fill) & all underwater metal fitting (including prop strut) daisy chained to each other, then connected to common ground with 8 awg 3. Large on-deck metal fittings, pulpits, stanchions, anchor roller daisy chained, then connected to lightning ground strip with 4 awg 4. No other connections to the lightning grounding strip, which begins fwd of mast, ends about 10' aft under galley. 5. DC negative terminates at negative bus 6. AC ground (not neutral) terminates at AC ground bus 7. Common ground point, engine or its own immersed copper plate? -- Questions -- What do I use for common ground for AC ground and DC negative: engine or separate, external copper bar, like with the lightning ground, but smaller? Engine has transmission, v drive, then out to prop The engine is freshwater cooled with raw water heat exhanger. Is there enough electrical contact in the cooling water system and the gears of the transmission and V drive use it for the common ground? Is the engine raw water intake metal thruhull electrically connected to the engine because the hoses are filled with seawater? What if water gets brackish? There would be no connection, if it was marginal to begin with. the water here can be salt, brackish, and sometimes sweet, if we've had a long run of rainfall. It seems that the more I reread Calder's book, the more I think using the engine/propshaft is not as good as a grounding plate outside the hull, esp. if I install a flexible coupling/drive saver. Is there any reason to connect the common ground to the lightning ground strip instead of its own ground plate (or engine/prop shaft)? Do I install a zinc to the external lightning ground strip? Thanks for the input.  

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Lightning protection on sailboats is an un-researched area of knowledge.  Most of the information is based on the theoretical physics of lightning coupled with experiential and anecdotal evidence.  This doesn't mean we know nothing about the matter. The articles and links below pretty much cover the ground and I suggest you read them over before deciding the level and complexity of any lightning protection system for you boat.  Two things seem clear:

• You CANNOT make a boat lightning proof, nor even much reduce the chances of a strike.
• You CAN significantly improve the chance you and your equipment will survive a strike.

Recommendations for Lightning Protection provided by the American Boat & Yacht Council, Standard E4.  (KP44 website page)

Grounding Your Vessel . Technical articles and links on grounding: on the kp44.org website

Air Terminals (i.e. lightning rods) by Ewen M Thomson, Univ. Fla. Sea Grant. 

Lightning & Sailboats . (i.e. lightning rods) by Ewen M Thomson, Univ. Fla. Sea Grant Publication. 1992. Very good publication.

Articles and Letters on Lightning and Boats by Ewen M. Thomson.  Terrific resource for lightning info.

World Wide Opposition to ESE Lightning Rods   from National Lighting Safety Institute, May 13, 2003.  (Article dated 1999, by Abdul Mousa).

Considerations for Lightning Protection. A very excellent analysis of the problem.  Presented in the blog of Domino – a 65' power catamaran.

Forespar "Lightning Master" Static Dissipater .  Supposedly "leaks off lightning causing ground potential".  Mousa, Thomson  (above) and others disagree, saying the ground potential on structures below 300 meters is meaningless in terms of lightning strikes.  

Lightning Master Corporation .  Surge protectors and Dissipaters.  DIssipaters are pretty much shown to be ineffective, but surge protection for onboard electronics is important.

Marine Lightning Protection, Inc. Founded by Ewen M Thomson. Best information on the web. Provider of air terminals and lightning protection systems . In particular look at his page on Grounding and Sidearc™ electrodes which is currently state-of-the art.

7 Answers About Boats Electrical Grounding Systems (Earthing)

Grounding is a term that discusses the process of preventing electrical shocks or electrocution in a home, in an RV, or on a boat.

It is essential to ensure that your boat has been grounded before you end up injured or shocked while on the water.

Grounding systems have particular requirements, which we will discuss how they should be installed on boats.

Here are 7 answers about boats and grounding:

Table of Contents

1. Should You Ground a Boat?

In regards to a boat, grounding is about bringing your electrical systems to a “zero voltage potential.” In Europe and other parts of the world, this is called earthing, or earth ground.

Grounding is a process that can be done on land or through the use of special circuitry, wires, and connections to the metal parts of the boat, including the engine.

Grounding is absolutely required to have safe boating experiences, but most boat users don’t know a lot about it.

Grounding not only prevents shocks and injury, but it also can protect the metals and wiring on your boat from corroding and reduces the chance of unintentionally draining the batteries.  

If you are confused about grounding, rewiring, or upgrading and how to do it properly, consider getting it done by a professional first before attempting to do it yourself.

2. How Do you Ground a Boat?

Grounding has two separate systems, often referred to as AC and DC grounding systems.  Besides, many boats, especially sailboats, have bonding systems that connect the metal rigging and major hardware to the metal through-hull fittings. 

These are different electrical equipment types and the processes that each needs to be properly grounded on your boat to keep it as safe as possible.

Often it is advised that boaters do not hook up their own electrical wiring for grounding, especially if they aren’t well-versed in boating-specific electrical components or don’t know the differences between grounding and electrical wiring.

If this is you, please seek professional help with your boat first!

Now, the basic premise for how to ground your boat is this:

AC (Alternating Current) Grounding System:

An AC grounding system is often referred to as a “free-floating” system. This means that they do not ground the boat directly to the vessel itself.  If you plug your boat into dockside electricity, the boat should have a galvanic isolator system.  These may not have been installed on older boats, so they should be added, probably by a professional.

This means that AC systems use a “neutral source” or “current-carrying conductor” to ground the boat and get it to zero voltage potential – basically to prevent it from shocking you or causing serious damage.

More specifically, the AC grounding system uses a dedicated ground or “green wire,” which is intended to channel a current safely in the event of a short circuit, therefore protecting anyone on board who might be touching metal at the time from getting a shock.

Note: the AC system should never be grounded to the bonding system!

If you have an AC grounding system, major connections will use green wires onboard your vessel. If you see them, make sure they are not corroded or uncovered, and be sure to leave them alone.

That green wire will redirect the current and send it back to its source, turning the power off if a short circuit occurs.

DC (Direct Current) Grounding System:

A DC grounding system originates at the battery.

It is also a free-floating system because it is never grounded to a metallic part of the boat. It is especially not grounded in the bonding system.

Instead, the DC grounding system works with negative potential rather than a neutral source like the AC grounding system. The battery provides that negative potential.

Furthermore, it is traditional for the DC system to be connected to seawater ground at one point ONLY on the boat – usually through its negative terminal or its “bus bar.”

A bus bar brings studs or terminals together in one “bus,” which becomes the electrical connection between one source to many other branch circuits.

Overall Grounding Information:

While you don’t need to know what a bus, terminal block, or other jargon is at this point, you do need to know what kind of grounding system your boat has.

Once you do, educate yourself on how to properly care for it or get it regularly maintained by a professional who can walk you through the process or do it for you at a reasonable price.

3. Do Boat Batteries Need to be Grounded?

Boat batteries are the primary connection used in a DC grounding system on your vessel.

The battery negative is connected to the engine negative terminal or bus in a DC grounding system, containing all electrical currents to the DC wiring. 

Batteries have a “floating ground,” which means that it doesn’t require an earth ground to work. The battery itself doesn’t have to be grounded before you touch it, and it most likely wouldn’t shock you with a wayward circuit.

However, if you are going to modify your battery connections on your boat’s electrical circuitry, make sure that you are confident you know how to properly attach it to the system – especially with the DC grounding system.

4. Should Aluminum Boats be Grounded?

Aluminum boats should be grounded like any other boat, but NOT to the hull of the boat.

An aluminum boat is a potential hotbed for electrical injuries and can be quickly be corroded drastically if it is exposed to electrical currents for too long.

All engine chassis should be insulated from the hull using spacer plates and insulating sleeves, and the propeller shaft should be insulated from the engine as well.

Ensure that you contact your mechanic or a professional who understands this process and can help or walk you through proper grounding.

5. How Much Does it Cost to Ground a Boat?

If you need your boat rewired, checked, maintained, or grounded in any fashion, you are most likely going to hire a professional.

Most boat owners don’t know how to wire their own boat, and they shouldn’t have to. Furthermore, doing it yourself could be incredibly dangerous!

Therefore it is important to seek out a marine technician who works specifically on boats – NOT cars.

It would help if you had someone who understands boating circuitry’s intricacies and who can do it right the first time.

That being said, this isn’t a cheap cost.

Most rewiring at a shop could cost you between $90-$120 an hour, not to mention parts, which adds another few hundred dollars on top of that.

A quick check on your boat would be cheaper to make sure everything is okay, but if you run into problems or want to upgrade or improve your boat’s electrical systems in any way, this will cost you far more in both time and money.

6. What Happens if you Don’t Ground a Boat?

Neglecting to ground your boat properly can result in electrical shocks, corrosion of the boat metals, or other injuries and damage to yourself and those on board.

It is crucial to know what kind of grounding system your boat has and properly maintain that system and check it often.

If not, you could go to touch metal parts or equipment on your boat one day and receive a terrible shock or even be fully electrocuted.

You could also cause extreme electrolytic corrosion, which eats away at your boat metals and disintegrates them very quickly.

While this is rare, it is still essential to stay on the safe side and prevent any potential injuries.

7. What if the Lightning Strikes on a Boat That is Not Grounded?

Your boat should absolutely be grounded no matter what.  Without grounding, you could be injured, shocked, or even corrode your boat and engine.

Electrolytic corrosion can cause the disintegration of boat metals on board.  This is prevented by the galvanic isolator on your AC system and by the galvanic anodes on the other major metals that are immersed in the water, such as the propeller and shaft.   

Galvanic corrosion can even completely corrode your boat propeller and motor in a matter of weeks if you aren’t careful.

Using Your Grounding System for a Lightning Strike:

Although your grounding system may lessen the effect of a lightning strike, the bonding system is designed to handle higher accidental currents, such as a lightning strike. 

There is much debate about how this works, but the bonding system is designed to maintain the same neutral voltage potential of the water around your boat, reducing the chance for a lightning strike.

If you want to add a bonding system to reduce the lightning strike’s potential damage, it requires adding to the wiring in your boat’s electrical systems.

It is recommended that your system uses a minimum of 6 American Wire Gauge (AWG) for your bonding conductors. Then you will need to use a minimum of 4 AWG or a “down conductor” for the wires at the metal through-hull fittings.

All in all, once you’ve added the proper upgrades, you should have a grounding system that can reduce the chance of a lightning strike and send it safely through the bonding system to prevent shocking you or harming anyone on board if a strike happens.

Remember: preparing for lightning strikes depends on the type of boat you have, so make sure that you know what upgrades to your system that your boat requires to do this properly.

References:

Why does a Circuit Always Have to Have Ground?

Marine Grounding Systems

Tips on Electrical System Use and Maintenance

Grounding Inverter/Chargers on Boats

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• About Lightning
• Frequently Asked Questions (FAQs) About Lightning
• Lightning Strike Victim Data

At a glance

Have a question about lightning? Check out our frequently asked questions and answers (FAQ) below.

General information

How can i protect myself from a lightning strike.

Be prepared. Check the weather before participating in outdoor activities. If thunderstorms are forecast, change plans or ensure that a safe shelter is nearby.

If inside during a thunderstorm, do the following:

• Stay off corded phones. Cell phones and cordless phones are okay.
• Do NOT use anything connected to an electrical outlet, such as computers or other electronic equipment.
• Stay out of the shower and away from other plumbing. This includes washing dishes.
• Stay away from windows and doors.

If outside during a thunderstorm, do the following:

• Seek shelter immediately.
• Do NOT lie on the ground or shelter under a tree.
• If no shelter is nearby, crouch down into a ball-like position with your head tucked and hands over your ears and your feet closely together

What is considered a safe shelter during a lightning storm?

A safe shelter is a fully enclosed vehicle or a shelter that has four walls and a roof. Examples of safe shelters include homes, offices, shopping centers, and hard-top vehicles with the windows rolled up. Open vehicles (such as convertibles, golf carts, and motorcycles) and open structures (such as porches, gazebos, baseball dugouts, and sports arenas) are NOT safe during a storm.

Can I get struck by lightning if there is no rain?

Yes. Even if you don’t see rain, you could still be at risk for a lightning strike. Lightning often strikes outside areas of heavy rain and can strike as far as 10 miles away from any rainfall. Many lightning deaths occur ahead of storms or after storms seemingly have passed. Remember, if you can hear thunder, you might be in danger of a lightning strike.

Does lightning ever strike the same place twice?

Yes. Lightning can strike the same place twice. In fact, lightning often strikes the same place repeatedly, especially a tall, pointy, isolated object. For example, the Empire State Building is hit by lightning about 23 times a year.

Indoor lightning safety

What should i do if i am inside during a thunderstorm.

To stay safe inside a building, do the following:

• Stay away from electrical equipment or cords, including corded phones.
• Avoid plumbing; do NOT wash your hands, take a shower, or wash dishes.
• Stay away from windows and doors, and stay off porches and balconies.
• Do NOT lie down on concrete floors or lean against concrete walls.

Is it safe to take a shower or bath during a thunderstorm?

No. Lightning can travel through plumbing. It is best to avoid all water during a thunderstorm. Do not shower, bathe, wash dishes, or wash your hands. The risk of lightning travelling through plumbing might be less with plastic pipes than with metal pipes. However, it is best to avoid any contact with plumbing and running water during a lightning storm to reduce your risk of being struck.

Are cell phones and cordless phones safe to use during a thunderstorm?

Yes. Cell phones and cordless phones are safe to use during a thunderstorm if they are not connected to an outlet through a charger. Do not use corded phones.

Outdoor lightning safety

What should i do if i am caught outside during a thunderstorm.

Do NOT lie on the ground. Lightning causes electric currents along the top of the ground that can be deadly more than 100 feet away. Get inside a safe location; no place outside is safe. Avoid anything that will increase your risk of being struck by lightning, such as being near or under tall trees. If there are no safe shelters in sight, crouch down in a ball-like position: put your feet together, squat low, tuck your head, and cover your ears. But remember, this is a last resort. Seek safe shelter first.

Is it safe to be under a tree during a lightning storm?

No. Being underneath trees is the second leading cause for lightning deaths.

Risk of being struck by lightning

What is my risk of being struck by lightning.

The odds of being struck by lightning in a given year is less than one in a million. You might have a higher risk if you work outside or live in certain parts of the country, such as Florida or Texas.

Who is at greatest risks for lightning strikes?

Males are four times more likely than females to be struck by lightning. Most lightning strike victims are people who regularly participate in outdoor recreation activities or work outside. Construction and farming are the two most common occupations for victims of lightning strikes. Regional and seasonal differences and time of day and year affect the risk of lightning injury (see Lightning Strike Victim Data ). For instance, most lightning strikes occur in the summer months, especially July, during the afternoon and evening. Also, southeastern states are particularly at risk, with Florida and Texas having the largest number of lightning-related deaths.

Lightning strike injuries

Is it safe to touch somebody who was struck by lightning.

Yes. Lightning victims DO NOT carry an electrical charge and you will NOT be electrocuted by touching someone who has been struck. It is safe to touch a lightning victim and administer first aid immediately.

What should I do if I see someone get struck by lightning?

Immediately call 911 for help. It is safe to touch a lightning victim and administer first aid immediately.

How many people are injured from lightning strikes each year in the United States?

Lightning strike injuries are not well documented. However, it is estimated that about 180 people are injured each year due to lightning.

How many people die from lightning strikes each year in the United States?

About 10% of people struck by lightning die. From 2006 through 2021, lightning caused an average of 28 deaths per year.

What happens to the body as a result of a lightning strike?

About 10% of people struck by lightning die, most commonly because of a heart attack. Other lightning injuries include blunt trauma, neurological syndromes that are usually temporary, muscle injuries, eye injuries (“lightning-induced cataract”), skin lesions, and burns.

How does lightning cause injuries?

Lightning can cause injuries in several ways:

• Direct strike : A direct strike is often fatal.
• Contact injury : Lightning strikes an object, such as a car or metal pole, that the victim is touching.
• Side flash : Lightning splashes or bounces off an object, such as a tree or person, onto the victim.
• Ground current : Lightning strikes the ground near a victim and the ground current passes from the strike point through the ground and into the victim.
• Streamer : When the air is charged with electricity during a lightning storm, bursts of energy, or streamers, can come upward from objects near the ground. Sometimes these streamers travel upwards through people, causing harm.
• Blast injury : The lightning's blast effect and sound might directly cause injury, such as ruptured eardrums, or might cause the person to fall or be thrown against an object.

You can protect yourself and your loved ones if you know what to do when you see lightning or when you hear thunder as a warning.

A vintage yacht washed ashore on a couple's property. The owner believes it was vandalism

Imagine waking up to find a 100-foot vintage yacht washed up on your property.

This was the strange and sudden reality for homeowners along the Dyes Inlet in Tracyton Monday, a quiet and serene jurisdiction in Kitsap County . Now, the neighbors are left to question how they’re going to get their view back.

“I just want to make sure this thing gets pulled out of here and the owner takes care of it,” said Cliff Irvin, who owns the property the vessel landed on.

As the tide gets low, the yacht tilts heavily to the side.

While the area’s recent high winds played a factor, KING 5 came to learn it was only part of the issue. We tracked down the owner, a man who interviewed with us but who preferred we did not share his name.

“We’ve been dealing with an ongoing stalker issue,” said the yacht’s owner.

He claims his yacht washed ashore due to vandalism.

“The new anchor line, the floating line got cut,” he said.

When someone told him that his yacht had started drifting, he said he climbed aboard to find three of his four anchor lines were cut. His lines were extremely thick and more durable than most, and they appeared to have been sliced with a special sharp knife or piece of machinery.

“And then we had this big windstorm and cameras,” he said. “And it would have held with two anchors, but someone had cut another anchor.”

He thinks he knows who did it because he said he has had this issue in the past with other boats he owns.

He even showed us texts he said his girlfriend got back in April after a similar incident with another one of his boats.

The screenshots read, “Hope your boyfriend enjoys his surprise on his trip,” and, “Making you watch him suffer is fun!”

A third text on the screenshot read, “Start chasing!!!!”

He and his girlfriend believe these texts came from the same vandal responsible for cutting the lines of his 100-foot yacht.

He said Bremerton police have now assigned a detective to his police case.

In the meantime, he plans to arrive back at the yacht’s beached location early Wednesday morning to try and tug the yacht back onto the water’s surface safely. He said the U.S. Coast Guard called him and threatened to fine him if he did not get it taken care of soon.

The yacht’s owner says there is no fuel on the vessel and is confident there is no leakage happening. However, the property owners said they are keeping a close eye on it.

Colorado lightning death is reminder of dangers as storm season arrives

A Jackson County rancher killed by a lightning strike Saturday is a grave sign that lightning season in Colorado is underway.

Mike Morgan, 51, was killed near Rand when lightning struck while he and other family members were feeding cattle. The bolt killed Morgan and 34 head of cattle nearby.

It was only the second lightning death in Jackson County since 1980, according to the National Weather Service.

Lightning ranks only behind floods and avalanches in outdoor-related deaths in Colorado.

Here is a look at what Colorado counties are deadliest for lightning strikes, when lightning strikes most often occur and separating lightning fact from fiction, according to the National Weather Service :

Here are quick facts on where Colorado ranks among states for lightning fatalities and flashes

There have been more than 100 lightning deaths in Colorado since 1980.

• 1980-2022: Colorado averaged two fatalities and 12 injuries per year.
• 2008-2018: Colorado was tied for seventh nationally in lightning fatalities. Between 1959 and 2019, the state ranked fourth.
• 2009-2018 : Colorado averaged around 500,000 lightning flashes a year, which ranked 19th nationally in cloud-to-ground flashes.

Larimer County among leader in Colorado lightning deaths

The last lightning death in Larimer County happened on Aug. 19, 2016, near Red Feather Lakes.

In Fort Collins, two men were fatally struck by lightning on the Colorado State University campus in July 2008.

Here are the top five counties in lightning deaths between 1980 and 2022:

• El Paso (Colorado Springs): 10 deaths, 84 known injuries
• Larimer County (Fort Collins): 10 deaths, 76 known injuries
• Jefferson County (Golden): 9 deaths, 38 known injuries
• Boulder County: 5 deaths, 31 known injuries
• Adams County (Brighton): 4 deaths, 14 known injuries

When lightning deaths/injuries happen most often in Colorado

Lightning deaths have been recorded in Colorado in April through October from 1980 to 2022.

• July: Deadliest month with 36 and most injuries with 165. June has seen 21 deaths and August had 18.
• Saturday : Day of the week with the most deaths/injuries with 57, followed by Sunday with 50.
• 2 p.m.: Hour with the most deaths/injuries with 51, followed by 1 p.m. with 40 and 3 p.m. with 37.

Here are the chances of being struck by lightning

• About 10% of those struck by lightning die, leaving 90% with various degrees of disability.
• The odds of being struck in a given year are roughly 1 in 1.2 million.
• The odds of being struck in a lifetime (80 years) are 1 in 15,300.

Lightning fact and fiction

It is true that you can roughly calculate the distance of lightning by counting the number of seconds between the flash of lightning and the sound of thunder, and then divide by five; 5 seconds = 1 mile.

But here are a few lightning safety myths and facts to remember:

• Myth:  Crouch if caught outside during a thunderstorm.  Fact:  Crouching is no longer advised because it doesn't make you any safer outdoors. Lying on the ground is worse. Run to a substantial building or vehicle.
• Myth:  If it’s not raining or there aren’t clouds overhead, you’re safe from lightning.  Fact:  Lightning often strikes more than 3 miles from the center of the thunderstorm and up to 15 miles away.
• Myth : A lightning victim is electrified. If you touch them, you’ll be electrocuted. Fact:  The human body does not store electricity. It is perfectly safe to touch a lightning victim to administer first aid. 
• Myth:  Rubber tires on a car protect you from lightning.  Fact:  It's true that most often vehicles are safe from lightning, but it is the metal roof and metal sides, not the rubber tires, that protect you. That's because when lightning strikes a vehicle, it goes through the metal frame into the ground — so don't be touching anything metal inside. The same goes for inside a house. Stay away from corded phones, electrical appliances, wires, TV cables, computers, plumbing, metal doors and windows.
• Myth:  Taking shelter under a tree is safe.  Fact:  Height, pointy shape and isolation are dominant factors of where a lightning bolt will strike, so this is not a good option. 
• Myth: Lightning never strikes in the same place twice. Fact: Lightning often strikes the same place repeatedly, especially if it's a tall, pointy, isolated object. The Empire State Building is hit an average of 23 times a year.

Five safety tips if outdoors when lightning is in the area

Before and while in the outdoors, continually make sure you have access to the latest weather updates.

In Colorado, thunderstorms typically develop in the mountains in the early afternoon, so plan to hike early in the day and be down the mountain by noon.

The first option is always to retreat to a safe building or a vehicle.

If you can't:

• Avoid open fields, the top of a hill or a ridge top.
• Stay away from tall, isolated trees or other tall objects. If in a forest, stay near a lower stand of trees.
• If in a group, spread out to avoid the current traveling between group members.
• If camping in an open area, set up camp in a valley, ravine or other low area but be aware of possible flash flooding. A tent offers no protection from lightning.
• Stay away from water, wet items such as ropes, and metal objects such as fences and poles. Water and metal do not attract lightning but they are excellent conductors of electricity. The current from a lightning flash will easily travel for long distances.

Here are safety tips if indoors when lightning is in the area

• Stay off corded phones. You can use cellular or cordless phones.
• Don't touch electrical equipment such as computers, TVs or cords. You can use remote controls safely.
• Avoid plumbing. Do not wash your hands, take a shower or wash dishes.
• Stay away from exterior windows and doors that might contain metal components.
• Stay off balconies, porches, and out of open garages or car ports.
• Do not lie on concrete floors or lean against concrete walls.
• Dog houses are not safe shelters. Dogs that are chained to trees or on metal runners are particularly vulnerable to lightning strikes.
• Lightning generates electric surges that can damage electronic equipment some distance from the actual strike. Typical surge protectors will not protect equipment from a lightning strike.

Lightning strike may be to blame for fire at Kentucky business

LONDON, Ky. (WKYT) - Witnesses say their surveillance cameras recorded a lightning strike, and moments later, fire swept through Huffman and Huffman Eye Surgeons on Main Street in London.

A thunderstorm was rolling through London Sunday afternoon when firefighters were quickly called to the North Main St. business for a fire in its roof.

“My first reaction was that it’s really bad. They are not going to put that out fast, there were flames coming out probably 10 feet high, from the roof, said owner James Huffman.

Fire officials say the exact cause isn’t known just yet, but people nearby say they have video evidence of a lightning strike.

“This gentleman over here actually filmed it through his ring doorbell. You can hear it and see it,” Huffman said.

Multiple fire departments battled the flames and five firefighters were sent to the hospital, or treated on scene for various injuries.

“The people transported were actually the first ones on scene, the original interior crew on the scene,” said London Fire Dept. Captain Brandon Wagers.

The business owners believe the building will have to be demolished, but they say they will be able to operate from another location. They may be down, but they’re not out.

They will be open for business Tuesday at London Women’s Care on Meyers Baker Road.

“We have had people helping us all day, bringing covered trailers and moving things out. We are blessed to have this many friends,” said Huffman.

They’ve been in operation for 33 years, and nothing like this has ever happened. They’re praying lightning does not strike twice.

The London Fire Dept. says they will do a cause of origin to determine what started the fire.

Copyright 2024 WKYT. All rights reserved.

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