sailboat propeller feathering

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Choosing the Proper Sailboat Prop

• By David Schmidt
• Updated: July 21, 2021

As sailors, it’s romantic to think that our locomotion comes from the wind, but most skippers, when pressed, admit to motoring a fair portion of the time. Like it or not, your boat’s propeller is a key element of the propulsion system, and just as there are myriad considerations involved when ordering sails, decisions abound when selecting the prop that best suits your wallet and sailing plans.

Fixed-Blade Options

As the moniker implies, fixed-blade propellers are typically cast out of an alloy such as manganese bronze or nickel, bronze and aluminum. Individual propeller blades stem from a central hub, which in turn attaches to the sailboat’s prop shaft or saildrive. Depending on the manufacturer, these blades typically are pitched in a way that propels the boat forward or backward when the transmission is engaged. The term “pitch” refers to how far forward or reverse a propeller will theoretically travel through a solid material (picture a screw twisting into a wood block). For example, a prop with a 12-inch pitch will theoretically move through 1 foot of solid material with each full rotation.

Sailors have choices available when buying a fixed-blade propeller, with the biggest variables being the ­diameter, the number of propeller blades, and the pitch. Just as sailboats create “dirty air” that spills off their sails, propeller blades push water against the hull, which then reverberates back (call this “dirty water”). When the transmission is in forward, this dirty water is sent back toward the rudder, which can influence steering. An important rule of thumb for all propeller designs and types is to ensure that the propeller has a tip clearance (the amount of space between a blade’s tip and the hull when the blade is in the 12 o’clock position) that’s at least 10 percent of the length of the prop blade (hub to tip). If you don’t have enough tip clearance, the next step is to spec a smaller-diameter propeller with an extra blade. Fixed props are available with two, three or four blades.

While this can be an easy fix, additional blades create additional drag when the boat is sailing. Because of this, sailors who opt for a fixed-blade prop are typically best served choosing a screw with the fewest number of blades that can properly fit their boat and their engine (see “Choosing Screws,” right). That said, additional blades equate to more power when motoring into a stiff headwind, current or big seas. Additional propeller blades can also accommodate a more powerful engine at a given diameter. These latter points are important if you’re planning on cruising unfamiliar waters and might find yourself negotiating a lee shore under power.

While fixed-blade ­propellers are strong, simple, relatively inexpensive, and ­easier to have repaired in remote locales, they do affect sailing performance. Moreover, they’re more likely to foul a lobster pot or other fishing gear than a folding prop when the boat is sailing. If you care about sailing performance, especially in the light stuff, or if you’re planning a long-distance cruise, purchasing a folding or feathering prop is a wise investment. But if you’re seeking maximum power or punch for your buck, and you sail on breezy waters such as San Francisco Bay, where extra drag isn’t a huge concern, a fixed-blade prop could be the way to go.

Folding Propellers

Folding propellers employ a series of gears (situated around the prop’s central hub and on the inboard end of each prop blade) and centrifugal force to open when the engine’s transmission is engaged. The slipstream action of the passing water acts to fold them closed when sailing, and their gear mechanisms hold the blades in their closed position even in light airs. As with fixed-blade props, sailors can choose between models that feature two, three or four blades. Unlike fixed-blade props, however, folding propellers create far less drag when the boat is sailing.

“For the same diameter and number of blades, folding propellers have 85 to 100 percent less drag than a fixed prop, depending on the fixed propeller’s blade area and the folding propeller’s make and model,” says Geoff Prior, owner of AB Marine, the Newport, Rhode Island-based importer and distributor for Gori folding props and AutoProp, Variprofile, and Variprop feathering propellers. “Geared folding propellers stay closed or folded when the boat is sailing, so a blade cannot drop down to be exposed to the water flow, and does not catch lines and weeds like fixed and feathering propellers can.”

Others agree. “Most sailboats will gain 0.5 to even 1 knot of speed by using a low-drag folding propeller,” says Keld Willberg, Flexofold’s general manager. “Many boat owners don’t look just at the speed gains, but also the ability to sail in very light wind.” Also, he says, when tacking, a boat that’s equipped with a low-drag prop won’t lose as much momentum.

This latter point is critical to anyone who sails in places with typically light breeze. “The folding propeller’s drag reduction and increased sailing speeds produce less turbulence over the rudder, enabling you to point higher, steer easier and more precisely, and tack and jibe the boat easier,” Prior says. “The biggest speed difference is in light or medium air and with clean water flow over the rudder—the boat is a lot more responsive, especially when fine sailing on the wind.”

One important consideration when selecting a folding prop is ensuring that your boat can physically accommodate the length of the prop when it’s folded. This is especially important on full-keel boats that have an aperture between the keel and rudder. For anyone who cruises with a saildrive(s), Prior advises that saildrive propellers must be approved for use by the saildrive’s manufacturer to ensure that the prop is electrically isolated from the saildrive’s leg and shaft; also the prop’s hub must incorporate a rubberized bushing to absorb shock and inertia, as well as an easily changed and ­streamlined anode.

As with all props, ­selecting the diameter, number of blades, and pitch of the propeller are all key decisions. “Diameter is the single most critical factor in determining the amount of power that a propeller absorbs and transmits into the water,” Prior says. “It’s the most important single factor in determining the amount of thrust delivered. The larger the diameter, the greater the efficiency. A small increase in diameter dramatically increases thrust and torque load on the engine and shaft.”

Blade count is also critical, but Willberg cautions that it’s overly simplistic to think that additional blades equate to additional power (see “Calling the Pitch,” right). “What ­matters is to get the right combination of blade area and pitch for the engine and gear box,” he says. “On flat water, a two-blade propeller can be just as efficient or even slightly better than a three-blade. However, when motoring against wind and waves, and when maneuvering, you get more power from a ­three-blade prop.”

Blade shape also matters. “Propellers with flat, planar blades are like a paddle,” Prior says. “The flat shape is not ­efficient at producing thrust because a flat blade is overloaded at the tip and underloaded at the blade base, whereas a fully shaped airfoil blade shape has a constant loading over its whole surface.” Much like fixed-blade props, most folding propellers employ an efficient blade shape, while feathering props use flatter and more ­planar-shaped blades.

One drawback of most (but not all) folding props emerges when the transmission is put into reverse. “In reverse, the suction side is on the back or aft side of a blade, and with the typical folding propeller design, the blades are trying to close in reverse, giving low thrust and lots of prop walk,” says Prior, who added that Gori’s three-blade prop presents identical leading-blade edges in both forward and reverse, negating this issue. Willberg advises that folding props require slightly different operation than fixed-blade or feathering props to ensure that they stay open. “For more stopping and reverse power, it’s just a matter of giving more revs on the throttle,” he says.

RELATED: Understanding Your Sailboat Propellers

As with all props, folding propellers must be kept clean of marine growth, and anodes must be regularly changed to ensure cathodic protection. “One millimeter of growth on a blade and your propeller loses approximately 12 percent efficiency,” Prior says, adding that this applies to any make, model or design. And, he notes, “folding propellers are water-lubricated, so they do not need to be greased.”

The final consideration is cost. Folding props are roughly four to six times more expensive than a fixed-blade propeller for a given diameter and blade count. While this is a big difference, the gains are huge, and—for bluewater cruisers—can translate to ­significantly faster passage times (potentially measured in days) and happier crews.

Feathering Propellers

As do folding propellers, feathering props greatly reduce drag when the boat is sailing; however, the way that they achieve this gain is significantly different. Moreover, the physics behind how the prop transitions from its sailing mode to motoring mode is also different.

Feathering props are available with two-, three-, four- and five-blade configurations. A central hub attaches to the prop shaft or a saildrive, and it features a series of internal beveled gears. Geared propeller blades attach to the hub and rotate through 180 degrees, depending on if the transmission is in forward or reverse (more on this later); this articulation is governed by machined stops inside the hub that prevent the blades from overrotating. When the transmission is engaged, the blades present their broad sides to the slipstream, but when the boat is under sail, the blades rotate 90 degrees to align with the flow of the water.

“Feathering props work off torque from the shaft or saildrive,” says Fred Hutchison, at PYI, which distributes Max-Prop feathering propellers. Because feathering props use torque—not centrifugal force—to open, it’s “instantaneous,” says Hutchison, who points to this as the design’s biggest advantage. “It takes a feathering prop only three-quarters of a turn to go from full forward to full reverse. In that time, the blades rotate 180 degrees, and it doesn’t generate much shock load.”

Prior adds, “In the sailing position, the water flow turns the blades to the feathered position when the engine is off for vastly reduced drag.” He estimates that this drag reduction is approximately 85 percent compared with fixed-blade props.

As previously mentioned, feathering-prop blades rotate through 180 degrees, which is a big advantage when operating in reverse compared with most folding props. “A feathering propeller gives reverse thrust with the same efficiency as in forward, as the leading blade edge in forward is turned 180 degrees, and without prop walk,” Prior says.

Another advantage of feathering props for boats with full keels or with tightly spaced skegs or rudders is that they “can fit in a small aperture as they have shorter overall lengths compared to folding propellers, which have a greater length when folded,” Prior says. “If there is a diameter constraint, the feathering prop can easily be designed and built with a higher pitch to make up for the loss of diameter and blade area.”

Most feathering props are machined out of a nickel, bronze and aluminum alloy, which, Hutchison says, makes them easy to repair. Unlike fixed or folding ­propellers, feathering propellers employ flat-shaped blades to reduce drag when the boat is sailing. “Feathering propeller blades are foiled and aren’t as efficient as the helical twist found on most fixed-blade or folding props,” Hutchison says, adding that manufacturers compensate for this less-efficient shape by increasing each blade’s surface area. “Blade surface area and shape make a big difference in how efficient it is,” he says. “No low-drag prop will be as efficient under power as a fixed-blade propeller.”

Lobster pots and fishing nets are common concerns when operating under auxiliary power, and feathering props are not snag-proof. “When motoring, feathering props are the same as fixed-blade and folding propellers,” Hutchison advises. “But when sailing, a folding propeller has less of a chance of catching a pot or fishing net than a fixed-blade or feathering propeller.” This is a consideration for anyone who cruises extensively in, say, Maine or in heavily fished waters off the West Coast.

As with all propellers, feathering props require basic care and maintenance to ensure their efficiency and the engine’s longevity. This starts with a properly spec’d and regularly refreshed anode, and the prop blades must be kept clean.

Unlike folding props, which typically use exposed self-­lubricating gears, the internal gears of feathering propellers need to be greased annually. While this adds an item to an owner’s yearly to-do list, Hutchison says that this can be tackled by a diver.

Finally, while feathering props are a great upgrade, they don’t come cheap. “Feathering props are more expensive than folding props,” says Hutchison, who ­advises that a feathering prop is roughly 10 to 15 percent more ­expensive than a folding prop with the same blade count and a ­comparable diameter. “This is primarily because of ­machining costs,” he says.

David Schmidt is CW ’s electronics editor and also writes about topics ranging from sailing gear to environmental issues from his home in Bellingham, Washington.

Choosing Screws

Choosing the right propeller is complex, but the most important variables for selecting the correct prop are your boat’s make, model, LOA and displacement, the engine’s horsepower rating and its maximum rpm, as well as the transmission’s reduction ratio. While most of this information is easily ascertained, determining the reduction ratio can be challenging. But, Prior says, “the best method to get the actual ratio is to use your cellphone camera and take a photo of the plate on the transmission,” adding that this beats hanging upside down and trying to read this information using a mirror and flashlight. For the DIYer, online calculators exist that can help crunch the numbers. “After that, it gets into the art,” Hutchison says. His advice: Ask an expert.

Calling the Pitch

Unlike fixed-blade propellers, feathering and folding propellers are often designed so that the pitch can be adjusted, perchance it doesn’t perfectly match your vessel, engine and transmission right out of the box. Depending on the prop, this adjustment is typically made by changing a screw(s) or swapping out the prop blades. These adjustments can usually be done by a diver while the boat is in the water. Some general rules of thumb as to when to change the pitch involve engine rpm: If the prop doesn’t meet the engine’s ideal rpm, the blade’s angle needs to be reduced; conversely, if the prop is exceeding the engine’s rpm metrics, the blade’s angle of attack needs to be increased. As a cautionary note, overpitching a propeller can cause the engine to overheat, and it can also lead to injector-choking problems and create excessive internal engine pressure, so be sure to stay within the engine ­manufacturer’s lines.

Vendor Information

EWOL: ewoltech.com , 410-317-8104; from $2,120

Flexofold: flexofold.com , 781-797-0809; from $980

GORI: gori-propeller.com , 401-847-7960; from $650

J Prop: betamarinenc.com , 252-249-2473; from $2,500

Kiwiprop: kiwiprops.co.nz , 877-549-4872; from $1,350

Max-Prop: pyiinc.com , 425-355-3669; from $1,900

Michigan Wheel: ­ miwheel.com , 800-369-4335; from $550

Variprofile: spw-gmbh.de , 401-847-7960; from $800

Variprop: spw-gmbh.de , 401-847-7960; from $1,200

Volvo: volvopenta.us , 800-522-1959; call for pricing

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Folding and feathering propeller test

• Emrhys Barrell
• March 24, 2015

Which is the best folding or feathering propeller for your boat? Emrhys Barrell compares 15 props in a test of speed, thrust, drag, stopping speed and propwalk

in 2009, Yachting Monthly tester Emrhys Barrell put 15 folding and feathering props through the most comprehensive test ever Credit: Graham Snook/YM

What’s the difference between a bucket and a fixed, three-bladed propeller? Not much, if you want to slow your boat down by at least half a knot when you are sailing. That’s the conclusion of our fixed, folding and feathering propeller test – the most detailed ever conducted as far as we are aware. A fixed three-bladed prop, locked in gear, exerts as much drag as hanging a bucket over the stern.

So what is the solution if you don’t want to sacrifice precious speed? The answer is, fit one of the many folding or feathering props on the market. But which one, and what are the drawbacks?

We measured the force generated by each propeller across the engine’s rev range

We tested all the props we could get our hands on (except the Volvo, Radice and J-Prop, which turned up too late for the test), measuring top speed under power, thrust (bollard pull) ahead and astern, stopping distance, and – for the first time anywhere – we measured the side-force (propwalk) generated when you put the engine into reverse.

We also measured propwalk while running astern. It’s a lot stronger than you think

It is this vital, unwanted component that sends you swinging off to one side when you try to stop suddenly, or back-up in the marina. We then towed three typical props behind a test boat to measure their drag, and how it compares to the overall drag of a yacht under sail.

Prop drag has been an issue for sailing vessels since the propeller was invented. Early trials were carried out on English warships, using jointed shafts that could be lifted into a trunk in the hull when sailing. In the 1890s, Danish pilot boats used similar lifting shafts.

For many years, long keels reduced the drag of two-bladed props on yachts, but the advent of the fin keel and exposed shafts brought the problem back again, with the added factor of more powerful engines making three-bladed props a necessity. The need to manoeuvre precisely in tightly packed marinas and overcrowded harbours has convinced even the owners of many long-keeled yachts to fit three-bladed props.

1970s: the first folding props

Most cruising skippers simply ignored the unwanted drag and loss of speed, but in racing circles it became increasingly significant. This led to the development in the 1960s and 70s of propellers whose blades folded backwards when sailing, reducing the drag markedly. The blades flew out under centrifugal force when the engine was put into ahead or astern. The earliest folding props had blades that moved independently, but this could lead to the lower blade dropping down when sailing, so the roots of the blades were linked with geared teeth, ensuring that they opened and closed together.

At the same time, an alternative approach was developed: the feathering propeller. Here, the blades were set at right-angles to the boss, as in a conventional prop, but on swivelling hubs. When motoring, the blades swing to the ahead or astern angled position, but under sail they ‘feather’, turning parallel to the boss.

One great advantage of feathering props is that they’re suitable for the many fin-and-skeg and long-keel yachts that have a small prop aperture in the rudder, where a folding prop won’t fit.

In the earliest feathering props, the blades remain in the same orientation to the boss in ahead or astern, as with a conventional fixed blade prop. In astern the aerofoil is working backwards, giving less thrust than in ahead. Some new feathering props have blades that swing right round, so the same leading edge is presented to the water in ahead or astern.

Cut prop drag by 90-95%

Under sail, the drag of folding and feathering props is tiny compared to a standard fixed-blade unit. Feathering props create about 5-10% of a fixed prop’s drag, sometimes less, while folding props have almost zero drag. This gives a significant gain in sailing speed, between half a knot and one knot, with the greatest percentage saving at low speeds.

Inevitably, there are drawbacks. The first is expense: a folding or feathering prop costs between two and six times more than a fixed equivalent. The second issue is complication – the gearing and folding mechanisms are prone to wear and corrosion in the salty and sandy environment, leading to reduced performance, and even loss of blades in extreme circumstances.

The third problem was performance under power. The early folding and feathering props produced less thrust than an equivalent fixed prop, particularly in astern, with dire consequences if the blades fail to deploy when you need to make a crash stop.

Now, the manufacturers claim to have addressed all the issues except cost. They claim the latest generation of their products give as good a performance or better under power, and major gains in speed under sail. We put their claims to the test on two chilly days in February. To our folding and feathering props we added a fixed three-blade prop as a benchmark, and the Axiom prop, a radical new development in fixed propellers, just to see how it compared.

Pitch, diameter, number of blades and handedness all determine a propeller’s performance

To help you understand our test, we will take a quick look at propeller theory and numbers. The four main figures you will see used to describe any prop are diameter, pitch, number of blades, and rotation.

Diameter is twice the distance from the centre of the boss to the tip of the blade. As a rule of thumb, the more powerful your engine, the bigger the diameter you will need.

Pitch is the measure of how far the propeller will advance in one revolution and thus how fast it will push your boat through the water for a given engine rpm (revolutions per minute). To understand pitch, imagine screwing a screw into a block of wood. The angle of the spiral thread governs how far it goes in for each turn. Similarly, the blades of a prop are set at an angle to the boss. The greater the angle, the greater the pitch. However, this is only the theoretical pitch. In practice, as water is not solid, the prop will slip to a degree and not advance so far. The amount of slip is around 30% for the props and speeds we are looking at.

Diameter and pitch are still measured in inches throughout the world – a quirk of history that would delight Henry VIII, and have Napoleon turning in his grave. But pitch can also be measured in degrees, especially relevant with feathering props whose blade angle can be varied.

The number of blades will vary between two, three or four, or even five in some high-speed craft. In practice, more blades will take greater power for a given diameter. For many years sailing boats used two-bladed props as they gave least drag in a boat with a full-length keel and an aperture for the prop, provided it could be locked in the vertical position. Today, most fixed props have three blades. Folding or feathering props have either two for cheapness, or three for higher power.

The hand of the propeller is the direction of rotation in ahead, when you are looking from astern. A right hand prop is one that turns clockwise in ahead.

Blade Area Ratio (BAR), sometimes called Disc Area Ratio, (DAR) is the area of the blades as a percentage of the area of a circle the same diameter as the prop. A prop with a greater BAR will take more power, but have more drag. Figures for sailing boat props are around 60%.

Incidentally, the explanation that a propeller advances just because its blades are angled forward is a convenient way to imagine what is happening, but not strictly correct. The blades of a standard prop are in fact aerofoil in section, like the wing of a plane, and move the boat forwards because as they spin round they develop lift. This lift is caused by a reduction in pressure on the back of the blade (‘back’ being confusingly the blade’s forward face). The faster they go, the greater the reduction in pressure. Once a certain point is reached, the reduction in pressure causes the water next to the blade to vapourise, and form bubbles. This is called cavitation, and limits the amount of power that a given area of blade can cope with. Also, as the bubbles collapse, they erode the metal of the prop, resulting in surface pitting on the back of the blade.

Our test boat was a Beneteau Oceanis 323 with a shaft-mounted fixed three-blade prop

We used a Bénéteau Oceanis 323, kindly leant to us by Sailtime in Lymington. She has a typical fin keel form, but atypically she has a built-in skeg carrying the shaft, rather than the P-bracket or saildrive of most other modern yachts. The skeg protects the shaft and prop from underwater damage, but a downside is increased vibration as the blades of the prop pass through the disturbed waterflow behind the skeg. This is resolved in normal use by fitting a three-bladed prop as standard rather than two, but otherwise did not alter the propulsive element of our test for either two- or three-bladed units.

The engine was a Yanmar YM20, giving 21hp at a maximum 3600rpm. The gearbox ratio is 2.6:1 in ahead, but somewhat confusingly a higher ratio of 3:1 in reverse. This is a very common engine/gearbox combination, so not an unreasonable test. Yanmar says it gives better thrust in astern, but in practice it meant the folding props were forced to use a compromise pitch. Some of the feathering props were able to set a different astern pitch.

We measured the force generated by the engine when running astern

We measured thrust, or ‘bollard pull’, in ahead and astern, throughout the rev range, using a load-cell borrowed from Diverse Yachts, with a remote read-out.

We then measured the side-thrust at full power in astern. This enabled us to predict the prop-walk created when you go into astern. To put this figure into context, the thrust produced by the worst prop in our test is the same as a 3hp outboard mounted on the transom, driving at right-angles at full throttle. No wonder so many yachts veer off to one side!

On the water, we measured speed through the rev range to maximum. We then carried out a crash stop from 6 knots. We recorded the time it took to bring the boat to rest at full throttle from the moment we engaged reverse gear.

To put these times into context, the distance the boat would travel before stopping would be 12m (39ft) with the best prop tested, but 17.4m (57ft) with the worst.

To measure the drag of all 18 propellers precisely enough to compare them with one another, making allowances for different yacht hull forms, we would have had to build a sophisticated testing rig, hire a team of scientists and spend several days in a research laboratory with a very large towing tank. Our objective was just to demonstrate the difference in drag caused by different types of propeller.

We tested the drag of three types of propeller using this test rig

We fitted a fixed prop, then a folding one, then a feathering one, to an outboard motor leg mounted on the transom of a lightweight 14ft skiff. We then towed the skiff at speeds up to 7 knots, and measured the difference in drag. We don’t claim this gave us the last degree of accuracy, but it was sufficient to compare with published drag figures. We then compared this drag to the hull-only drag of the Océanis 323 – a typical 10m cruising yacht.

A question of some gravity, Mr Newton

To keep things simple, we have presented our drag and thrust figures in kilograms (kg). Strictly speaking, thrust is a force and should be measured in Newtons – 1kg is multiplied by the acceleration due to gravity to give a figure of 9.81N. On another planet, with different gravity, our units would be wrong, but until we hear they are holding regattas on the canals of Mars, we will rest our case.

The results

Featherstream three-blade

Made in England at the time of writing (2009), this is a three-blade feathering unit with a bronze boss, and stainless steel blades. The pitch of the blades can be adjusted externally, and can be different for ahead and astern. The blades swivel 180º to present the same leading edge in ahead and astern. As a result, it performed well in astern: second best for bollard pull and third for stopping distance. However, occasionally it would not open in astern, and you had to learn to snap the throttle hard to get it to deploy.

Max Prop three-blade

Designed by Massimiliano Bianchi in 1976, the Max Prop was one of the first of the new generation of props. Boss and blades are bronze, and the pitch can be set as you assemble it, or by the factory if you want a different astern pitch. The blades swivel 180º to present the same leading edge in ahead and astern. It gave the best astern thrust, and was in the middle of the pack for stopping distance. It never missed a beat going into astern.

Max Prop two-blade

A two-blade version of the Max prop. As expected, it gave some vibration on our test boat, but this would not occur on a yacht with a P-bracket or saildrive. Mid-range performance for astern thrust and stopping distance.

Kiwi Prop three-blade

Designed in New Zealand in 2000, this is only available as a three-blade unit. The boss is stainless steel, and the blades are glass-reinforced Zytel plastic. Each blade has two different aerofoil sections, as you move out from the boss. It has no internal gears, so each blade feathers independently according to the waterflow over it. The blades do not swing completely round in reverse, so the trailing edge becomes the leading edge. It was one of the simplest to fit – just slide it on and tighten the nut. Mid-range for astern thrust and stopping distance, but the lowest top speed. It also went easily into astern.

Brunton’s Autoprop

Brunton’s Autoprop marked a completely different approach to feathering props when it was brought out in 1987. The three blades are linked together, going from fully feathered while sailing, or in neutral, to fully twisted under power. The difference is that when you go into gear, the amount they rotate depends on engine speed and loading. Thus the ahead or astern pitch varies according to engine rpm, which, Brunton claims, improves performance and fuel economy, with reduced rpm for a given cruising speed. We can confirm the latter: our tests show the Autoprop achieved 6 knots at 2,100rpm, compared to 2,500rpm for our standard prop and most of the others on test. However, previous drag tests have shown that this is achieved at the expense of slightly more drag than other feathering props, though still 80% less than a fixed prop. Bollard pulls were on the low side, but it still achieved near the maximum top speed, with mid-range stopping distance.

Autostream three-blade

From Australia comes the Autostream, a three-bladed feathering unit that has been in production for 20 years. Construction is all-stainless steel, with the blades swivelling 180º to give the same leading edge in astern as ahead. Separate ahead and astern pitch can be adjusted by the owner without dismantling the prop. It has been designed to stay feathered at speeds up to 25 knots, helped by extra blade area aft, making it suitable for fast multihulls. On test, it gave the fastest stopping time of all the folding or feathering units, plus significantly lower side-thrust than the rest, while still maintaining good ahead speed.

Variprofile three-blade

This is a three-blade feathering prop, made in Germany. The blades swivel 180º to give the same leading edge in astern, and the pitch can be set differently for ahead and astern. Usually, this is set in advance for the customer, but can be altered on site. Blades and boss are bronze, with stainless pins, and an anode aft of the nut. Ahead thrust was low, but stopping distance was good.

Flexofold three-blade

Made in Denmark at the time of writing (2009), the Flexofold is an all-bronze folding unit, with stainless steel pins, and the anode cleverly enclosed by the blades. On test, it gave the equal highest forward thrust of all props, and highest top speed. It also had one of the lowest side-thrusts. Astern performance was the best of the folding props. At a cruising speed of 6 knots, the engine was turning at 2,300rpm, compared to the 2,500rpm of our standard fixed prop and most of the others on test.

Flexofold two-blade

A two-blade version of the Flexofold, its performance was only slightly down on the three-blade, and in fact better for astern thrust. Again, it had some vibration due to the skeg. A racing two-blade version is also available.

Gori three-blade

Another of the earliest folding designs, the Gori has been made in Denmark since 1975, in two and three-blade versions, but the company only recommended the three-blade for this boat. They also make a racing two-blade version, with reduced drag. The blades have a three-way gearing system for opening and closing. Boss and blades are bronze, with stainless steel pins. A speciality is its overdrive feature, which sets the blades in a coarser pitch if you open the throttle gradually while the boat has forward way on, which allows you to cruise or motorsail at lower rpm for more comfort. Performance ahead and astern were towards the bottom of our list, with the longest stopping distance, but the prop-walk was third best.

Slipstream three-blade

From the same Australian company as the Autostream comes the Slipstream folding prop. Again the boss and blades are stainless steel, which gives greater strength, allows thinner section blades, and removes the need for an anode. The bearings are bronze bushes, while the blade gears are bevelled, with two rows each, claimed to better chew up any barnacles that might chose to grow on them. Polyethylene side thrust washers further improve the opening action. On test it performed in the middle of the folding props, though with comfortable low cruising revs of 2,250rpm at 6 knots.

Slipstream two-blade

Similar in design to the three-blade version, though with slightly worse astern figures, but it still made 6 knots at a low cruising rpm of 2,350.

Varifold two-blade

Made in the UK, this is mid-way between a racing and cruising prop, with the blades closing tightly for low drag, but still having enough shape to give good motoring performance. As a result of its close fit, you have to give the engine a burst of throttle to get the blades to open initially. It has a bronze boss and blades, and stainless steel pins. It gave equal highest top speed, but was near the bottom of astern performance.

Axiom three-blade

Axiom fixed three-blade

The Axiom is the joker in our pack. It is not a folding propeller, but it does have a revolutionary blade profile and section, if you will pardon the pun, and has never been tested on a yacht before, so we just had to put it into our trials to see how it compared. As the photograph shows, the blade profile is rectangular, while the blade section is almost S-shaped, and symmetrical in ahead and astern, with no twist. Its designers claim it gives greater thrust and stopping power, together with lower wash. So how did it stand up? Well the charts show the story, with its stopping time nearly a second better than any other model, and its side thrust again the lowest by far. However this was at the expense of lower top speed, which suggests some more tweaking is needed, but it is still one to watch.

Drag curves

Drag v speed

In the graph above, you can see that at 5 knots, a fixed three-blade prop with its shaft locked creates almost half as much drag as the entire hull. The drag can be halved by allowing the prop to spin, but the gearbox may suffer. By contrast, the drag of a feathering prop is negligible, and the drag of a folding prop is too small to plot on a graph of this scale.

The hull resistance curve for the Océanis 323 was calculated for YM by the Wolfson Unit, at the University of Southampton, using data from the Delft University Systematic Series. The propeller drag curves are based on data from SSPA Maritime Consulting, using Volvo S-drives. This data were verified by YM’s on-the-water drag test.

All but three of the propellers on test produced less prop walk than the standard fixed prop. The fixed Axiom and feathering Autostream were the best performers, but nearly all the folding props fared better than the rest of the feathering propellers.

Maximum speed

There was more than half a knot of difference between the best-performing props and the worst. Four folding propellers and one feathering prop managed to prove the claim of better performance than a standard fixed prop, but nine of them fell slightly short.

Interestingly, some of the best performers were two-bladed props, which are widely assumed to perform worse than three-blade versions.

Bollard pull ahead

The fastest props are generally also the most powerful in ahead, and most of the slower ones are among the least powerful. However, only one unit – the three-bladed Flexofold – generated a greater bollard pull than the standard fixed prop. The most powerful props produce almost a third more thrust than some of their rivals.

Bollard pull astern

Three propellers produced a more powerful bollard pull than the standard fixed prop in astern: two folding units and the newly designed Axiom. Nearly all the feathering props performed better in astern than the folding ones – some by a very wide margin. There’s a huge difference between the best and worst-performing props – the three-blade Max Prop has almost twice the bollard pull of the two-blade Varifold.

Stopping time

The new-concept Axiom prop excelled in this test, but nearly all the feathering props were better at bringing the boat to a standstill than the standard prop. The folding props were less effective and some of them were less than 100% reliable when called upon to perform an emergency stop. The difference between the best and worst stoppers was about 3½ seconds. It may not sound like much, but in a crunch, it could make all the difference.

If you want to add up to a knot to your boat speed, then fitting a folding or feathering propeller is a must, not just for racing boats. And as our test demonstrates, you can usually still retain the handling and performance under power that you had with a standard fixed-blade prop. In fact, often you’ll get better performance.

Five of the tested props gave more speed than the standard prop, with four of them being folding models, and both Flexofolds coming out top. And even though it was only 0.15 knots better, when you look at the hull resistance curve this is a considerable improvement. On the other hand, with astern performance, in general it was the feathering props that came out best, with better bollard pull than the standard, and better stopping times, and the Autostream coming out top. The folding props were generally not as good as the standard, though in the main only by no more than 10%.

But it was the prop-walk figures that proved the most interesting. Ten of our test units gave less prop-walk, with generally the folders coming out best, but the top units being the Axiom and Autostream, with 30% less side-thrust than the standard fixed three-blade, a considerable advantage when you have to stop suddenly or back-up in a marina.

In terms of resistance, our test shows that letting your fixed-blade prop spin, if the gearbox manufacturer will allow it, halves the drag. But to get the real improvement, fitting a folding prop will give at least 95% less drag than a locked, fixed propeller, while a feathering unit will give at least 92% of the drag – still an enormous saving.

But these benefits do have a price, literally on your wallet. A 16in fixed three-blade propeller will cost around £300 (2009 prices in UK). But the cheapest two-blade folding prop will be at least double this price, with most of them between £600-900. For a three-bladed folding unit expect to pay between £1,200 and £1,600. Feathering props are even more expensive, starting at around £1,200 for a two-blade model, rising to £2,100 for the most expensive three-blade version.

Because of the wide variation in cost, performance and specifications of the all the units tested, we have not felt it appropriate to recommend a best buy. The tables and curves give you the information you need at a glance, allowing you to make your own decisions as to which is best for you and your boat.

Some are easy to fit, others difficult. Professional installation is advised for such an important – and expensive – bit of kit

Some of the props on test are very simple to install, others are very complicated. However, while they all have instructions for DIY fitting, unless you’re very confident in your own skills, a piece of equipment as vital as a propeller ought to be professionally installed, both for safety and peace of mind. For our test, we had every prop fitted by the manufacturer’s representative, so there was no question about the installation, and they also observed all our measurements.

Bronze has been the material of choice for propellers almost since they were invented. Strong, resistant to salt-water corrosion, it is also easy to cast, with a low melting point, as our ancestors found out 4,000 years ago. Stainless steel has been making an appearance recently. Even stronger, it allows thinner and so more efficient blades. It is even more corrosion resistant, and also harder, so less vulnerable to impact damage. However, it has a much higher melting point, so it is more difficult and expensive to cast and machine.

Maintenance

A folding or feathering prop will need more maintenance than a fixed prop

Whatever prop you have, it should be checked every time the boat is lifted, for wear, corrosion and movement. Folding and feathering props do require more maintenance than fixed ones. Some bosses are packed with grease, which should be repacked annually. Some have nylon shims or bearings, which should be checked, especially in silted waters. Most have an anode, which should be checked and replaced if necessary.

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NEW! Variprop GP

14% greater performance, get up to 14 percent greater performance and extended cruising range with the new variprop grand performance (gp) feathering propeller. for shaft and saildrives., aero foil shaped blade.

The only feathering propellers on the market with Gawn blade profile (aero foil shaped blade). The Gawn profile blade is more efficient, producing no vibration when motoring and very low drag under sail.

14% Reduced Fuel Consumption

SPW’s innovative design of the Variprop GP has achieved up to 14% reduction in fuel consumption while also delivering high thrust, extending your cruising range and reducing CO2-emissions.

The all new Variprop Grand Performance (GP) propellers are based on the company’s proven technology and provide ever better performance, reliability, efficiency, fuel efficiency and longevity in all conditions.

Unique Variprop Features

A. Independently adjustable external pitch control. Forward and reverse pitches can be changed in just seconds — even underwater.

Benefits: Custom fine tuning (in micrometer-small increments) of reverse thrust vs. prop-walk. (For most owners, eliminating prop walk is more important than maximizing reverse thrust.)

VARIPROP allows you to customize that balance for optimum control, maneuverability and safety. Independent fine tuning of forward thrust means that VARIPROP delivers the best possible performance (speed, thrust, fuel economy) in forward without compromising reverse performance – and vice versa

B. SoftStop™ shock absorber – Shock Absorbing Multidisc Brake (patented) built into the VARIPROP hub.

Benefits: Dramatically reduces shock loads on gearbox and drivetrain, permits shifting at higher speeds without damage, preserves preset pitches by eliminating hard limit stop impacts (the typical “clunks” of all others). The entire drive train benefits: longer cutless bearing life, minimized wear on gearbox, clutch plate, bearings.

SoftStop™ shock absorber lets you shift smoothly and extends the longevity of the whole drive.

Variprop GP 2-Blade

For small yachts with engines from 6 to 40 hp

Variprop GP 3-Blade

For all sailing vessels with engines from 6 to 180 hp

Variprop GP 4-Blade

For open sea vessels with engines above 100 hp

Quality Construction

All propellers sold by AB Marine are manufactured from NIBRAL, a metal alloy made of nickel, aluminum and bronze. NIBRAL is far stronger in all specification areas than manganese bronze (commonly used by other prop manufacturers).

Tensile Strength

Impact strength, fatigue strength, 0.2% proof strength, cavitation erosion resistance, corrosion resistance, would you like to discuss variprop propellers without obligation.

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Feathering Marine Propellers                                         

Feathering propellers provide a host of advantages over folding and fixed blade propellers for sailing vessels, whether cruising or racing. Conceived and designed specifically for sailors, feathering propellers increase sailing speeds by reducing drag, they improve boat maneuverability (i.e. eliminating prop walk) and they reduce wear on drivetrain components. Our feathering propellers are easy to install, easy to adjust pitch, and built tough with premium materials to handle the rigors of ocean life.

We are proud to offer two superior lines of feathering propellers. EWOL and J-Props are two of the best products in the industry. Call us to discuss our propeller options that are suitable for your vessel.

Why a Feathering Propeller?

• Increase Sailing Speeds –  Up to 1.5 knots more under sail
• Greater Performance Under Power – Micrometric pitch settings allow you to optimize cruising speed
• Improved Handling – Improved Backwards Thrust Virtually Eliminates “Prop Walk”
• Easy Installation, Maintenance and Removal

EWOL & J-Prop Advantages

• Easy Adjustment – No tools needed! Simply pull and turn hub to adjust pitch. No costly haul out necessary.
• Precision machining. Use of helical gears ensures reduced wear and enhanced durability.
• High quality materials. Super tough aluminum-bronze alloy and stainless steel construction offer enhanced corrosion protection and durability from prop strikes.
• Low maintenance. Simply add grease annually (can even be done in the water).

J-Prop 2 Blade Feathering Propeller

J-prop 3 blade feathering propeller.

EWOL ANDROMEDA – 3 Blade Feathering Propeller (13”-17”)

EWOL ORION – 3 Blade Feathering Propeller (19”-24”)

Ewol orion – 3 blade feathering propeller for saildrives (15”-18”).

J-Prop 4 Blade Feathering Propeller

J-Prop EP Feathering Propeller

J-Prop Saildrive Feathering Propeller

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Ewol feathering propellers make maneuvering easier, increase sailing speed and increase cruising speed under power

EWOL adjustable pitch propellers are made of stainless steel alloys that represent the highest technology in terms of marine corrosion and galvanic corrosion resistance, and are also equipped with the most refined technical solutions that make it unparalleled on the market.

EWOL feathering propellers can be fitted on sailing boats with both traditional (endothermic) and electric engines and with both mechanical and hydraulic inverters. The components of EWOL propellers are made of super-duplex stainless steel alloys, developed by the steel industry for extremely heavy tasks.

EWOL regularly presents new versions of its products with increased performance, and is now also working on developing additional innovative products that will come out in the short and medium term. Nowadays, anyone seeking a truly reliable product that performs over time, solves boat manoeuvrability and sailing speed problems, and is always up at the cutting edge of technology and materials, should install an EWOL propeller on their boat.

Benefits of Ewol propellers

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Reduce Drag When Sailing With A Folding Or Feathering Propeller

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Learn how this time-tested piece of running gear can give your boat a power boost under sail.

Photo: Stacey Nedrow-Wigmore

One thorny debate among sailors is whether it's better to let a propeller freewheel (rotate while sailing) or to lock the shaft and hold the prop steady. Whichever camp you fall into, there's no denying that a fixed prop creates drag that slows down your boat.

Consider this: If your boat has a fixed three-blade prop, you could be losing as much as a knot of speed when sailing (as verified in an independent test of several props by the author aboard his own 33-foot sloop). In other words, if your boat typically cruises around 5 knots, switching to a folding or feathering propeller could ramp up that speed to 6 knots — that's a 20% increase! Over a typical 30-mile voyage, that translates to arriving one hour sooner.

Folding and feathering props are nothing new and have been around in one form or another for more than half a century. Early props had just two blades that relied solely on centrifugal force to open them. While these props work well enough for many sailors, they have a few shortcomings: They don't work too well when maneuvering around the docks, especially when backing. And should one blade open slightly more than the other, excessive vibration can occur, causing wear to the shaft log and cutless bearing.

Newer types of folding props, such as the Flexofold , may have two or more blades interconnected to each other with a gear mechanism. This ensures that when the shaft starts rotating, they open symmetrically. Other brands include Gori Prop , Varifold , and Slipstream .

However, folding props may not work for some boats, especially if the rudder is close to the propeller hub preventing the propeller from completely folding. In this instance, a feathering prop, such as the Max-Prop , may be a better choice. Other brands include Kiwiprop and Variprop . With a feathering prop, the blades are symmetrical and rotate around a central pivot point and offer as much thrust in reverse as they do in forward gear — a boon for getting into a tight slip. When sailing, the blades align themselves with the flow of water, reducing drag.

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PERFECT PROPULSION WITH

The autoprop, autoprop feathering propeller.

The Autoprop feathering propeller for cruising sailing yachts, displacement motor vessels, to 350hp. 

Autoprop’s unique design and superb build quality make it the first choice feathering propeller among cruising yachtsmen the world over, with drag reduction when sailing by at least 85%, and a unique ability to change pitch automatically to suit prevailing wind and sea conditions when motoring or motor sailing. Auto pitching, auto feathering, the same thrust in astern as ahead, less prop-walk in astern, a brand new version for hybrid and purely electrically driven vessels, and a recently developed ability to produce very efficient and economic propulsion for purely diesel powered displacement motor boats are more than reason enough.

​ Autoprop is a unique propeller which has been praised by yachting writers around the world. Whatever type of cruising sailing yacht you may own, mono or multihull, or displacement motor vessel, leisure or commercial. If you need more information don’t hesitate to contact us.

“Our tests show the Autoprop achieved 6 knots at 2100 rpm compared to 2500 from our standard prop and most of the others on test” 

Yachting Monthly

IN DRIVE MODE

You can see from the image Autoprop in drive mode. When reversing the blades swing through 180 degrees and produce the same thrust as in forwards. When sailing the blades feather automatically, reducing drag by up to 85%.

HOW AUTOPROP WORKS

Autoprop is the cruising yachtsman’s propeller ‘par excellence’. As you can see from the animation on the right Autoprops blades can rotate through 180 degrees and the subtlety of their design allows them to produce the same amount of thrust whether the yacht is in ahead or astern. It is a unique propeller which, unlike its competitors, excels in all aspects of a cruising yachts use and does not compromise any of them.

Whether you are sailing, motor sailing, or motoring, Autoprop will dramatically enhance your yachts performance.

THE BENEFITS OF AUTOPROP

The image above of the feathered Autoprop shows how, when sailing, Autoprop reduces drag by up to 85% compared with a three blade fixed propeller; with the two blade propeller the reduction can be even greater.

​ This drag reduction can equate to as much as one additional knot in sailing speed.

With other feathering and fixed pitch propellers performance under engine is a compromise. No such compromise exists with Autoprop, her blades admittedly rather an odd shape, are the result of a huge investment in design time and testing. The Autoprop blades, unlike those of conventional propellers, maximise the thrust delivered whatever rpm the yachts engine is running at.

MOTOR SAILING

Autoprop automatically varies its pitch depending on the conditions. Put simply, as the wind or sea conditions vary so does the blade pitch of your Autoprop. The less pressure the Autoprop feels on its blades the more pitch is applied and vice versa.

​ The result is maximum efficiency whatever the conditions, with increased speeds at lower engine revs and lower fuel consumption and emissions.

MANOEUVRABILITY

In reverse the Autoprop blades swing through 180 degrees and present exactly the same blade shape as they do ahead.

​ The result, the same excellent thrust, with greater stopping power and less prop walk.

ADVERSE CONDITIONS

Likewise in adverse weather conditions, the vessel’s speed will be reduced because of the adverse weather such as high winds and choppy sea conditions. The Autoprop senses the load acting upon it and reduces the pitch angle allowing the engine to run to a higher maximum rpm.

Much like travelling up a hill in your car, you need a lower gear ratio to allow the engine to run faster and produce more power.

This unique feature of the Autoprop, enables the full power of the engine to be used in situations such as towing, or in emergencies. With conventional propellers because the pitch is too coarse at very low speeds, the engine cannot achieve its full revolutions and therefore full thrust is not achievable.

DOWNLOAD OUR BROCHURE

The Autoprop brochure describes in some detail the unique benefits that you will obtain after you have fitted one to your vessel.

​ If, between the brochure and this website, you find yourself still with unanswered questions, please do not hesitate to contact us using any of the methods on the contact page.

DISCOVER OUR MODELS

Propellers Diameters 330mm to 430mm or 13″ to 17″

Shaft Diameters 22mm to 30mm or 7/8″ to 1.25″

Power For engine up to 40hp

Propellers Diameters 380mm to 510mm or 15″ to 20″

Shaft Diameters 22mm to 35mm or 7/8″ to 1.5″

Power For engine rated to 75hp

H6, H9 & H62

Propellers Diameters 470mm to 900mm or 19″ to 35″

Shaft Diameters 35mm to 75mm or 1.5″ to 3″ Power For engine rated to 350hp

• Suitable for all leading makes of saildrives.
• Rubber insert prevents shock loads being taken by the shafting in the saildrive leg.
• Double nut locking feature ensures secure fitting to saildrive leg.

Propellers Diameters 330mm to 510mm or 13″ to 20″

TESTIMONIALS FROM OUR CUSTOMERS

Nothing tells a products story better than owner’s own experiences and with Autoprop the message is one of satisfaction in every department: performance under sail, performance motor sailing, performance motoring, build quality and strength, and in our new green world, economy. One of Autoprops earliest and greatest supporters is Sir Chay Blyth who, in the ’90’s’ fitted all of his BT Challenge yachts with Autoprops. He summed up his Autoprop experience saying, “I can highly recommend Autoprop propellers to all sail boat owners who want the very best performance under power and sail.”

​ We have selected just a few of the many messages we’ve been sent by owners explaining why Autoprops provide all the benefits in the first paragraph and more. They also reflect the vast range of craft, from traditional wooden yachts to fast modern catamarans, that have all hugely benefited from fitting the unique Autoprop.

AUTOPROP REVIEW ON A COLVIC COUNTESS

Amel Trust Autoprop

Jeanne Socrates

From Arctic to Antarctic

Xplore – Steel Going Strong

Seastar Sailing Fleet Fit Autoprop

Autoprop fitting and servicing.

Fitting and servicing Autoprops could not be easier. When you receive your Autoprop it comes ready assembled and one nut is all it takes to secure it to your yacht.

​ Servicing is just as simple, with routine cleaning for ballbearing types and cleaning and greasing for rollerbearing types being all that is needed when the yacht is lifted. Unlike many of our competitors propellers all the wearing parts of an Autoprop are replaceable.

​ Listed below are fitting and maintenance instructions for all our models. They are in PDF format for easy viewing or downloading…

SAILDRIVE OWNERS MANUAL

Saildrive versions bearing replacement instructions, shaft versions owners manuals, shaft versions bearing replacement instructions, take a look, our video help, fitting a shaft drive, fitting to a sail drive, removing an autoprop, what the magazines say, yacht magazine, voile magazine, vela e motore, seil magazine, if you have any questions, please phone us on +44 (0) 1255 420005, uk office available weekdays 9:00 – 18:00.

Tel: +44 (0)1255 420005 [email protected]

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Feathering and folding propellers

Fitting a folding or feathering propeller gives you an extra knot under sail, and improves marina handling, jake kavanagh finds.

In today’s market, there are three clear solutions to reduce propeller drag. The first is the folding propeller, where the blades quite literally fold closed. The second is the feathering prop, where the blades turn parallel to the flow of water, presenting a minimal profile. The third is the self-pitching featherer.

While swapping your existing prop for a swing blade alternative may be a significant outlay, perhaps £1,000-£2,500 or more for a high-quality feathering model, it will be a long-term investment that will keep paying back. This could mean better fuel economy and longer engine life, but also in the sheer pleasure of using your boat. She will point slightly higher, suffer less paddle wheel effect, and give you a bit more performance under sail.

Folding props

Usually the simplest and cheapest way to minimise drag, the folding propeller can have up to four blades that close in on themselves from as little as one knot under sail. Because the propeller relies on centrifugal force to hold it open in reverse, the blade section is much thicker and heavier than usual. Higher revs are also needed. Folding props are best suited to faster, fin keeled yachts that handle well under power, and where reversing is less critical (the exception being the Gori design).

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Feathering props

The blades are designed to set themselves in a position perpendicular to the water flow, and because they need to present a neutral cutting edge to the water, the blade profile is almost flat. This means that the prop is slightly less efficient than a curved blade when driving ahead, but because the pitch completely reverses when the engine is going astern, this gives enhanced stopping ability and more powerful sternway. Feathering props can usually be repitched easily by adjusting the point at which the ‘flipped’ blades meet their stops, and even re-handed by moving the gears a couple of notches.

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Better Sailing

Fixed Vs Folding Vs Feathering Propeller

Out of sight, out of mind goes the saying, so it often is for your boat’s propeller. Crucial as this piece of equipment is to your safe and rapid movement from a to b, it often receives very little attention. You simply set it and forget it – until something goes wrong. That’s a shame because most new boats are fitted with fixed-blade propellers as standard, and older boats often have them too. While that is fine when the engine is running ahead, a fixed propeller is inefficient astern. It applies real drag to a boat under sail.

Tests vary in their scientific-ness, but  data suggests that a fixed prop that is locked creates at least 20 times as much drag vs a folding or feathering propeller at 5kt. In speed terms, that equates to some 20% more pace with a folding or feathering propeller vs a fixed one. That data suggests that folding and feathering props are much better than fixed.  Crossing the North Sea from Harwich to Ijmuiden means that it could save you four hours.

Folding or Feathering?

Folding propellers – where the blades close up around the central boss – are marginally more efficient in sailing mode than a feathering prop, that has blades that simply rotate to a position parallel to the direction of movement. This makes them the racer’s choice, but it is a narrow margin and pales into insignificance next to a fixed prop. A feathering prop is nearly as efficient as a folding prop when going ahead and typically a bit better astern. Feathering blades can be more suited to long keel boats where the prop is enclosed, providing insufficient space for a longer folding prop.

On the other hand, a folding prop is less apt to tangle with fishing pots and waterborne debris. In the early days of these designs, folding props could be reluctant to fully deploy when going astern. However, manufacturers claim this tendency has now been eliminated. Tests suggest that they are far more effective astern at high revs rather than low and can cause a loud clunking noise when they deploy. 

Propeller Diameter

This is a measure of the prop’s size and refers to the width of the circle that the blade tips turn through. It is twice the distance from the center of the boss to the tip of a blade. In general, the more powerful your engine, the bigger the prop diameter needed to utilize that power effectively.

Propeller Pitch

The blades of your propeller slant or curve forward (or back in reverse) – this is what part of what generates the motion. This pitch is usually measured in inches and refers to the distance the propeller would advance in one revolution if it gripped the water perfectly. Imagine your prop is a screw; the pitch is how far into the wood the screw advances with one full turn.

The steeper the pitch, the more work the engine must do with each revolution. A standard pitched propeller will ensure that the engine can just reach full rpm at full throttle. Some sailors like being overpitched, however. It puts more strain on the engine, which means it will never reach peak revolutions, but it’ll keep the boat moving a bit faster through the water until peak power. Turning over more slowly, the engine is a bit quieter and more efficient.

Some props have a variable pitch, automatically adjusting to the pace of the boat and revs of the engine. Others allow the pitch to be changed via a turn of a screw on the boss or require the boat to be hauled out.

Prop Blade Number

This is essentially down to you. Fewer blades mean less drag – hence the reason that so many fixed props are two-bladers. But with the exceptionally low resistance of a fixed or a folding prop, this is barely an issue. On the other hand, there can be more vibration with a two-blade model than a three or more blader. And more blades give more power. Most cruising yachts have three blades.

Best Folding and Feathering Props

The Gori is a folding prop that claims to have the thrust of a fixed prop. Made from nickel aluminum bronze, the blades are geared so that they cannot open or close independently. They pivot through 180 degrees to give the same pitch in forward and reverse, which means optimum speeds in both directions. Uniquely, Goris have an ‘overdrive’ function for motor sailing, which deepens the pitch of the prop to give the same power from lower engine rpm.

With the lowest drag of any folding prop, according to some German tests, Goris are used by the Volvo Ocean Race boats and many of the racing one-designs, as well as cruising brands.

Bruntons’ feathering propeller is a technical marvel with either two or three blades that rotate perpendicular to the prop shaft. Because each blade’s weight is offset, they will rotate through 180 degrees between forward and astern, giving them the same optimum pitch in both directions. Free to rotate on their axis, the blades will adopt varying pitches, according to the needs of the boat.

So, when you are motor sailing, they pitch up to account for the driving force of the sails, reducing fuel consumption and engine rpm. This feature should also reduce prop walk astern.

Also manufactured by Bruntons in Essex using high-quality nickel aluminum bronze, the Varifold is designed to appeal to racers and fast cruisers. As a folder, it offers less resistance in sail mode than its Autoprop sister. 

The company claims a unique design for the blades of the prop that cuts noise and vibration. A helical pitch, including reduced pitch towards the blades’ tips, reduces pressure and noisy pulses against the yacht’s hull.

Featherstream

This UK-built propeller is manufactured using aluminum bronze for the hub and stainless for the blades. There is no standard spec for their props because Darglow prefers to talk through a client’s requirements in detail first. 

The pitch on a Featherstream is determined by the pitch cassette installed with it. This can’t be altered when the boat is in the water. Still, it is always possible to send off for a differently pitched cassette from Darglow and install it via a 10-minute operation when the boat is hauled. If you send the old cassette back, this is cost-free. 

The blades are completely flat for frictionless sailing and rotate through 180 degrees for optimum power ahead and astern.

Maxprop blades are flat and pivot through 180 degrees so that the leading edge is presented in both forward and reverse – making for excellent thrust either way. 

Pitch can be changed in 2-degree increments at the turn of a screw, which can even be done in the water with the Easy and the Whisper models. It is not quite the variable pitch that the manufacturer claims, but it does offer some flexibility. The blades are linked by gears, so they open and close at the same time. 

Maxprop says its products are particularly good for catamarans.

Unlike all the other propellers featured here, the blades of the Kiwi Prop are a special nylon-glass composite called Zytel. Glass may seem an odd choice for a propeller. Still, the material is incredibly tough, lighter than metal, and corrosion-free. It is also much cheaper than bronze, a fact reflected in the lower retail prices. The manufacturer also points out that the blades are sacrificial in the event of a collision and much cheaper to replace than potential repairs to the stern gear. 

The blades are fatter than some but symmetrical, free to rotate around their axis for excellent feathering. The boss allows the blade assembly to rotate 100 degrees, offering adjustable pitch ahead and maximum pitch astern for more power at low speeds. 

Kiwi is also developing a two-blade folder. 

This feathering prop is entirely made of 2507 duplex stainless steel for exceptional strength and resistance to corrosion. It features narrow blades that swing through 180 degrees in reverse. 

Pitch is independently set for ahead and astern and can be easily adjusted – as can direction of rotation, if a change of engine necessitates it.

The folding prop from Seahawk is also in stainless steel – but this time low carbon 316 for long life. 

The blades are geared, so they are synchronized, and the bushes can be replaced easily when worn. Plastic bump stops prevent the prop from clunking when it swings open, and the same polyurethane forms side plates to stop metal-on-metal wear. Seahawk provides a five-year warranty.

The Flexofold uses high-quality nickel aluminum bronze in its construction. Being water lubricated, its gears need no grease. Its simplicity and competitive price have made it the go-to prop for many boatbuilders. It has large shock absorbers for quiet opening, and in tests, it performs well both ahead and astern. Also available in a special race variant with a corrosion-free composite boss that saves 2.8kg of weight.

The Variprofile is a robust prop, built to order in ice-class nickel aluminum bronze for an extremely long life. Like most feathering props, the blades are flat and thin, and they rotate 180 degrees in reverse to offer the leading edge in both ahead and astern. A simple turn of a screw is enough to change the pitch, which can be independently set in both directions – ahead, it is all about optimizing thrust, while in reverse, it is about reducing prop walk. A patented multidisc brake acts as a shock absorber to eliminate the clunk when you engage the prop. Its short hub makes the prop really suitable for long keeled boats with a small prop aperture.

Variprofile

Similar to its Variprop, Variprofi le is SPW’s cheaper, small-boat feathering prop. It is mass-produced for modern serial yachts with engines up to 140hp. Otherwise, it has many of the same features as its custom-built sister, including micro-adjustment for the forward and aft pitch.  

Peter is the editor of Better Sailing. He has sailed for countless hours and has maintained his own boats and sailboats for years. After years of trial and error, he decided to start this website to share the knowledge.

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Feathering or folding prop recommendations?

• Thread starter danstanford
• Start date Sep 7, 2019
• Forums for All Owners

danstanford

Wanting to increase our racing results next year and working on the best elements to address. B323 with two blade fixed prop which sings so I have a perfect justification to get it off the boat! Cost is not an issue if it is better. Sailing in fresh water with little risk of snagging lines, but weeds can be a significant issue in some years in some harbors. I want to be able to cruise under power when needed but most of the time the prop is just to get me out into Lake Ontario and back to the dock. For me, prop walk is not an issue though less would not be a problem when I have the rare southerly across my slip causing me to need to back to port out of the slip and down the fairway which can be a challenge. The most important issue for me is the risk of no reverse when I need it and this seems to be a risk with the folding props....is it? In summary, decent motoring and solid reliability is all I need but I really want to increase performance under sail, particularly in light winds. Advice?  

kappykaplan

I like my Maxprop.  

Davidasailor26

We switched from our OEM 3 blade fixed to a 3 blade flex-o-fold a couple seasons ago and love it. The PHRF hit for changing the 3 blade is 9 seconds, but the speed improvement in light winds is minutes not seconds. Prop walk is about 50% of the fixed, just enough so that I can still use it to my advantage when needed, without being overpowering. Speed under engine is basically the same as the fixed prop, maybe 0.1 knots more at cruising RPM. Thrust in reverse is noticably less than the fixed prop, so when I'm coming into the dock and need to slow down I rev to 1200 or 1500 RPMs instead of idle. Never had a problem with it not unfolding. No required periodic maintenance or lubrication; I just polish it quickly each winter. I've read some reports that the 2 blade FOF is more susceptible to vibration issues, so you may want to consider that, but that aside I have nothing bad to say about it.  

My understanding is that a folding prop will be faster sailing and a feathering prop is a better prop especially in reverse. I have a folding and it has been a big improvement. Motoring is fine.  

Reverse is no problem with my Gori 2 blade folding prop.  

Went to a FlexOFold two years ago. Marked improvement in acceleration, and overall boat speed.  

I have had Goris on two boats and am very satisficed with the performance. Equal thrust in forward or reverse, very little prop walk, folds to almost no resistance. Can increase speed from .5 -1.25kts sailing. Another advantage, OVERDRIVE, excellent for motoring if necessary. Will pick up 1kt to 1.5kts boat speed at same RPM.  

DayDreamer41

We have a FlexoFold on our 41 and find no notable performance issues  

Love my Maxprop classic  

• Under sail, prop drag is only a factor for lighter air, where you have insufficient power to overcome friction. In 20 knots, you can drag a bucket behind and it won't slow you below hull-speed.
• In lighter air, you can expect a significant improvement from a folder, and slightly less from a feathering prop, e.g. moving you from 4.5 to 5 kts in a drifting race for a 30 foot boat. How often are you racing in winds under 10 kts in your area?
• If you cruise the boat, what is your decision point for motoring? If I am moving less than 4 kts and I have someplace to go, I'll motor-sail the rest of the way. Usually, I set this number for each passage.
• Based on the studies I've read, folding props are 80% of fixed props for forward, but really lack efficiency in reverse. Feathering props are 90% efficient in both directions, which is even slightly better than a fixed for reverse.
• At slow / docking speeds, a great deal of inefficiency and prop walk can be overcome by changing how you handle the throttle. Expect to learn to handle the boat differently when you get the new prop, but do not let the few minutes of docking determine which prop to buy.
• Most prop manufacturers recommend mounting on stainless steel shafts. If you have bronze, figure in the additional cost of the shaft and labor to replace. Might as well do your cutlass bearing and think about a dripless seal at the same time. $hit adds up!

Parsons said: Under sail, prop drag is only a factor for lighter air, where you have insufficient power to overcome friction. In 20 knots, you can drag a bucket behind and it won't slow you below hull-speed. Click to expand

Parsons said: Based on the studies I've read, folding props are 80% of fixed props for forward, but really lack efficiency in reverse. Feathering props are 90% efficient in both directions, which is even slightly better than a fixed for reverse. Click to expand

Parsons said: Putting together a speed improvement for your boat is a combination of factors, but here are some points that we can discuss: Under sail, prop drag is only a factor for lighter air, where you have insufficient power to overcome friction. In 20 knots, you can drag a bucket behind and it won't slow you below hull-speed. In lighter air, you can expect a significant improvement from a folder, and slightly less from a feathering prop, e.g. moving you from 4.5 to 5 kts in a drifting race for a 30 foot boat. How often are you racing in winds under 10 kts in your area? If you cruise the boat, what is your decision point for motoring? If I am moving less than 4 kts and I have someplace to go, I'll motor-sail the rest of the way. Usually, I set this number for each passage. Based on the studies I've read, folding props are 80% of fixed props for forward, but really lack efficiency in reverse. Feathering props are 90% efficient in both directions, which is even slightly better than a fixed for reverse. At slow / docking speeds, a great deal of inefficiency and prop walk can be overcome by changing how you handle the throttle. Expect to learn to handle the boat differently when you get the new prop, but do not let the few minutes of docking determine which prop to buy. Most prop manufacturers recommend mounting on stainless steel shafts. If you have bronze, figure in the additional cost of the shaft and labor to replace. Might as well do your cutlass bearing and think about a dripless seal at the same time. $hit adds up! BTW: I went through this decision model for a club racer, but mainly cruiser, and it said "Maxprop" and $5,000. How important is that extra knot to you? Click to expand

danstanford said: In the final analysis, an extra knot would be worth $ 5k to me but I am not at all sure I will see that much coming from a two bladed prop! Click to expand

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Seahawk Low Drag Stainless Steel Feathering and Folding Sailboat and Yacht Propellers

Seahawk's autostream and slipstream propellers have moved to nsw.

Autostream S1/S2 3 blade feathering Yacht propellers

Feathering Propeller Features :

• Strong reverse thrust better than a folding or fixed blade propeller
• All major parts cast in 316 and 2507 stainless steel
• Easy to replace bronze and acetal bushes
• S2 model has a rubber insert to absorb shocks and can be replaced
• Simple external pitch adjustment
• Sizes from 15 to 20 inches diameter
• Rated for up to 75 horse power
• S1 model fits taper shafts up to 1-3/8 inches diameter
• S2 model fits 17 Spline Sail drives
• S2 fits 109mm Gearcase Sail Drives like : Volvo 130/150 and Yanmar SD20 SD31 SD50 SD60
• S2 model does not match : small 89mm Lombardini Sail Drives and small Volvo 120s Sail Drives

Slipstream S5 3 blade folding Yacht propeller

S5 Folding Propeller Features :

• Less chance of catching kelp and ropes than a feathering propeller
• All major parts cast in 316 stainless steel
• Easy to replace bronze blade bushes
• Sizes from 14.5 to 18.5 inches diameter
• S5 model fits taper shafts up to 1-1/2 inches diameter

Slipstream S7 3 blade folding sail drive Yacht propeller

S7 Folding Propeller Features :

• Rubber insert to absorb shocks can be replaced
• S7 model fits 17 spline sail drive shafts like
• Volvo 130/150 and Yanmar SD20 SD31 SD50 SD60

Slipstream S4 2 blade folding Yacht propeller

S4 Folding Propeller Features :

• Less drag than a 3 blade folding or feathering propeller
• Sizes from 14 to 20 inches diameter
• S4 model fits taper shafts up to 1-1/4 inches or 30mm diameter

Slipstream S6 2 blade folding sail drive Yacht propeller

S6 Folding Propeller Features :

• S6 model fits 17 spline sail drive shafts like

Folding Propellers vs. Feathering Propellers

Last Updated by

Daniel Wade

June 15, 2022

Unlike a fixed propeller, which is known for creating a substantial amount of drag when sailing, fitting a folding propeller or feathering propeller will increase your speed under sail while significantly improving marina handling.

One of the most debatable and divisive issues in sailing is the varying schools of thought as far as the best sailing propeller is concerned.

Whether you believe in using the motor as your main propulsion or you fall in the purists' category who believe that a propeller should only be used for getting in and out of a marina, one thing is for sure: propeller drag is and has always been a major issue for sailboats since the invention of propellers.

While fixed three-blade props are essential in providing superb motoring performance, they can negatively affect your speed and performance when under sail. To avoid this, you should consider choosing between folding propellers and feathering propellers.

Fixed propellers are known to cause significant drag that can negatively affect your sailing speed and performance when under sail. This means that we're only left with two options: folding propellers vs. feathering propellers.

The debate generally revolves around whether you should let the propeller rotate while sailing or put a stop to the spin

Studies have proven that folding and feathering props can create less drag and in turn enhance your boat's speed and performance, especially when compared to fixed props.

But even after discarding fixed props for the considerable amount of drag that they cause, we still have to choose between folding propellers and feathering propellers.

This is what this article is all about: folding propellers vs. feathering propellers. At the end of this read, you should be able to differentiate the two and choose the right one for your sailing escapades.

Table of contents

The Importance of Choosing the Right Propeller for Your Sailboat

Your sailboat's propeller plays an integral role in enhancing its speed and performance. Whether you're planning to make a long-distance passage or trying to outrun an approaching storm, you probably have realized that an extra knot makes a whole lot of difference. An extra knot can not only save you time but also be the difference between life and death, so it should never be taken for granted.

That's not all, choosing the right propeller brings with it some sort of a feel-good-factor knowing that you're getting the best from your sailboat. It will give you the peace of mind that you deserve when out there on the water while enhancing your boat's performance and speed.

Unfortunately, choosing the right propeller for your sailboat isn't a walk in the park. If anything, choosing between a folding propeller and feathering propeller brings forth a multi-dimensional problem in terms of the level of performance, efficiency, price, maneuverability, safety, and many more. This is exactly why you should know what they are, what they will do to your boat, and the best one to go for.

Folding Propellers

A folding propeller is essentially a type of propeller that is often mounted at the aft end of a boat's keel. It is designed in such a way that its blades automatically fold out when the engine is used to power the sailboat and fold back when the boat is under sail and the engine isn't working. When the engine is on, folding propellers will spin outwards by a centrifugal force. On the other hand, the water flow forces will push the propellers back when the engine stops.

Folding propellers come in various forms and may range from the most basic types to highly sophisticated geared folding propellers. The most sophisticated ones might be costly but are quite efficient and will provide top-notch performance both ahead and astern while significantly reducing all forms of drags.

We have to note that folding propellers can be ideal for easily driven lightweight sailboats or if you do not want to ignore the unwanted drag and significant loss of speed. Folding blades are also essential in racing circles. They generally fold backward thereby reducing drag significantly and increasing speed and performance under sail.

Benefits of Using Folding Propellers

You've probably been wondering why many sailboat owners have been choosing to use folding propellers on their boats. Well, the benefits that these types of propellers bring to your sailing adventures in terms of speed, performance, and safety are unmatched.

Here are some of the benefits.

Reducing Drag

Numerous tests have consistently shown that folding propellers create the least amount of drag when sailing, especially when compared with feathering propellers or fixed propellers. The two-blade versions of folding propellers are the most efficient in reducing drag, especially when going astern.

Most two-blade folding props can perform just as well as three-blade folding props. However, their simple design of opening independently of each other can sometimes cause imbalances and vibrations, especially if one of the two blades open or close more than the other.

There are also three-blade and four-blade propellers that bring to your sailing game an interesting overdrive characteristic. These blades generally work by reversing automatically when going astern. This feature is important when the engine is on as it can be essential in saving fuel when using the engine to sail in calm conditions.

Folding props generally have better thrust when moving forward than feathering propellers but this will, of course, depend on the pitch as well as the shape of the blades. The prop will go astern if they have a weak point. This is because they rely on the centrifugal force to hold the blades open against the force trying to close them. You have to keep in mind that the blades might not be as efficient as it if going forward if the blades are open.

Offering Safety

The blades of folding propellers don't usually stick out as they do on feathering props or fixed propellers. This means that there are no chances of the prop catching debris or any marine creature. Needless to say, such issues can lead to a loss of steering ability and ultimately cause an accident. In short, your safety is much better if you're using folding propellers.

Greater Maneuverability at the Dock

Folding propellers are generally designed with powerful shapes and hydrodynamic designs that can give your boat greater maneuverability like you would at the sea. These props are designed with superior stopping, forward, and reversing power.

As we noted earlier, folding propellers are the most efficient in reducing drag, which generally affects the speed and performance of your boat. So by installing a folding prop, you will improve your sailing performance and speed by nearly 15%. Your boat will be faster and the voyages will be more enjoyable even in lighter winds.

More Comfort

In an ideal sailing situation when the wind is optimal and the weather is calm, you're likely to hear the sound of the propeller, especially if it's a fixed propeller. The resultant noise can be frustrating but this should be an issue in folding propellers. If anything, the noise levels will be as low as the drag. This is because most folding props are designed with strong built-in shock absorbers to reduce the noise levels.

In short, folding propellers are ideal if you want to reduce noise and vibration that are common in fixed blades.

Great Value for Money

If you've owned a sailboat before, you already know that having a propeller that's designed with various moving parts can be costly in terms of repair and maintenance. This is essentially why many sailboat owners prefer props with just a few moving parts.

As such, folding props can be ideal since their only moving parts are the blades. They are also structured with smooth acting gears and strong materials to ensure durability without any need for greasing, rebuilding, replacements, or maintenance. In essence, folding props will ensure that you spend most of your precious time sailing instead of being at the dock fixing your boat.

Similarly, folding props are known for having lower initial purchasing cost than feathering props. They have a simpler design, which significantly reduces the purchase costs. In short, folding props are more affordable than feathering props.

Cons of Folding Props

Despite these numerous benefits, folding propellers have noticeable downsides that we have to highlight. They include:

• ‍ The fixed pitch that cannot be removed or changed once fitted. If you have to change or remove the pitch, you'll have no choice but to seek the services of a propeller expert.
• Although this may vary depending on the brands, folding props have simple designs that tend to wear out the fastest when compared to feathering props.
• Folding props have inadequate reverse thrust, so you'll have to be very skillful to maneuver tight dock spaces.
• The gears are most likely to be exposed to the marine environment and, therefore, will wear out quickly.

Are Folding Propellers Ideal For Your Boat?

Folding props can be ideal for you if you have a small or medium-sized sailboat with moderate engine power. You'll not only attain extra speed under sail but drag will be a thing of the past. Additionally, folding props can also be ideal for motor sailors and larger boats. So if an extra knot is essential for you, folding props might make much sense.

Again, you'll have the peace of mind knowing that your safety is guaranteed as far as your boat's propeller catching debris or causing an accident is concerned. Its design can prevent seaweed from getting tagged along or anything that might make you lose your steering ability and perhaps cause an accident.

Feathering Propellers

Feathering props operate exactly as the name suggests: the prop blades feather when the engine is on neutral or shut down. They generally feather in the passing water flow in the same way a sail positioned head-to-wind would. It has a small profile that is essential in reducing drag while enhancing speed and sailing performance.

The blades of a feathering prop are designed in such a way that they set themselves perpendicularly to the water flow. This gives them a neutral cutting edge to the water, which makes the blades almost flat. As such, such types of props can be less efficient when sailing ahead since the pitch will be reversed when the engine is going astern. Fortunately, you can repitch your feathering prop by simply adjusting the point at which the flipping blades meet but you'll have to move the gears a couple of notches.

Benefits of Feathering Propellers

Here are some of the benefits of using feathering propellers.

Offers Superb Maneuverability

Generally speaking, feathering props are positive in their function. The blades or the feathering props will be opened by the torque of the shaft. It doesn't matter whether it has seaweed or not, the feathering props will open because of the torque of the shaft that reduces unnecessary shock load. The fact that it has the best thrust in reverse and commendable thrust when moving forward gives it superior maneuverability even in tight docking situations. You'll also not need any skills to maneuver the boat at the dock.

Offers Amazing Reverse

Feathering propellers are widely popular not just because of the superior maneuverability that they bring to your sailing adventures but also because of their incredible reverse features. The blades can rotate 180 degrees in turn of the shaft, thereby giving them a very high level of efficiency on both the reverse and forward thrust.

This will improve your level of control even on the reverse while decreasing prop walk. In essence, the feathering props are much better than fixed props or folding props in reverse. They should, therefore, be your first choice if you're looking for a prop that can give you complete control of your sailboat even in tight spaces. These types of props are also very durable as they're more robust in construction than folding props.

Even though not on the same level as folding props in terms of reducing your boat's drag, feathering props are much better than fixed props. To put it into perspective, a 26-foot sailboat is likely to create about 50 pounds of pull if it has fixed props while the same boat would create 4 pounds of pull if it's fitted with feathering props.

Adjustable Pitch

Unlike folding props that have fixed pitches, feathering props do have pitches that you can easily adjust to optimize the performance of your boat. The systems used by each brand can vary but you can set independent reverse and forward even when on the water. This can also help in reducing the prop walk.

Cons of Feathering Propellers

The most noticeable downside of feathering props is their expensive prices. Feathering props generally cost twice as much as folding props and this can be a major hindrance if you're on a tight budget. You'll also have to service and maintain the props due to their complex designs. Again, you might have to deal with a given level of drag, which makes them less efficient as far as speed and performance are concerned.

Are Feathering Propellers Ideal for Your Boat?

Simply put, feathering props can be ideal for you if you're looking for efficient maneuverability, especially at the dock. These types of props allow you to thrust forward and reverse even in tight docks. As such, this can be a good option for novice sailors as there are no technical skills required to maneuver the boat even in tight conditions.

To this end, we hope that you can make the right decision in choosing between folding propellers and feathering propellers. While they are much better than fixed propellers, the most ideal one for your boat will certainly depend on your specific needs.

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I've personally had thousands of questions about sailing and sailboats over the years. As I learn and experience sailing, and the community, I share the answers that work and make sense to me, here on Life of Sailing.

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Yacht Cruising Lifestyle

Everything fun you can do from your yacht

How to Choose the Right Sailboat Propeller

November 10, 2021 by Martin Parker 1 Comment

Introduction

Choosing the right sailboat propeller for your needs is a complex process. Make the wrong decision, and you could end up with an underpowered boat or a constantly over-revving engine. Get the right propeller, though, and your engine will run more efficiently and with less vibration, ultimately allowing for more comfortable cruising.

By understanding propeller basics and seeking the advice of professionals, you can easily find the right propeller for your sailboat. Below, we explain the basics so that you know what to look for when buying your next sailboat propeller. We’ll also take a deep dive into the choices of propellers available for purchase.

Propeller Basics

Before we jump into the more technical details of propellers, it’s essential that you know the basic parts of a sailboat propeller and what they do. Understanding the basics will help you choose the right propeller and give you some knowledge when speaking to the experts.

The hub serves two purposes. First, it connects the propeller to the driveshaft, allowing the engine to turn the propeller and drive the boat forward. Second, the blades are attached to the hub, either as a one-piece casting or using some mechanical means.

There are three terms relating to the blades.

Root: The point where the blade attaches to the hub.

Leading-Edge: When rotating, the blade edge cutting through the water is the leading edge, while the opposite side of the blade is the trailing edge.

Tip: The furthest end of the blade from the hub.

Basic Dimensions

Two measurements define the basic propeller dimensions, the diameter and the pitch, and propellers are described in terms of their pitch and diameter.

The size of the circle made by a rotating propeller. Imagine attaching a marker to the end of a blade and then spinning the propeller one full rotation, with the marker drawing a circle on a piece of card. Measure the distance across the circle, and that is the propeller’s diameter.

The distance the propeller would move forward during a single rotation. Think of a nut and bolt. The pitch of the bolt’s thread is equivalent to that of the propeller. When you rotate the nut through a single rotation, it moves forward a set distance. The distance moved is the pitch, measured in inches.

Sailboat Propeller Sizing

Both diameter and pitch are measured in inches, and the values describe the prop size. A 14/22 prop has a diameter of 14 inches and a pitch of 22 inches. While these dimensions will give you a reasonable propeller size for your boat, other factors also affect the correct values for your propeller.

Your Propeller Choices

When you are considering a new propeller, you have a significant number of choices to make. Some may be forced on you by budget constraints. Others you may deem essential regardless of cost.

Constant or Variable Pitch

The pitch is the blade’s angle of attack through the water, and blades either have constant or variable pitch. A constant pitch blade has the same pitch from root to tip, whereas the pitch of a variable pitch blade reduces towards the tip. When you look at it, a variable pitch blade twists from the hub to the tip.

If your budget is tight, you may opt for a constant pitch prop, as they are cheaper to manufacture. However, a variable pitch prop offers better efficiency and is generally the better choice.

To understand why variable pitch is more efficient, we need to look at propeller speed. As your propeller spins at a constant engine rpm, the hub turns much more slowly than the tip of the blade. Increasing propeller speed equals increased thrust, so to maintain constant thrust along the blade, the pitch reduces towards the tip.

Fixed or Controllable Pitch

Fixed propellers all have twisted blades giving a variable pitch along the blade, but the pitch cannot be adjusted as the name suggests. This makes them cheaper to produce than variable pitch props.

A variable pitch prop allows the blades to be rotated at the root, allowing you to set the correct pitch for varying conditions. Because of the increased cost and complexity, variable pitch blades are rarely seen on cruising yachts and are primarily used on superyachts. There are several advantages that you may consider worth the extra cost;

– Your engine rpm can be set at the most economical speed, with thrust controlled by varying the pitch.

– You may be able to reverse the pitch of your propeller, which is very useful when maneuvering. This eliminates the need to stop the propeller from spinning before changing its direction.

– A variable-pitch propeller can be fine-tuned to get the best efficiency, power, and speed from your propulsion system, something you cannot do with a fixed pitch prop.

– Variable pitch propellers can often be feathered. The reduced drag and therefore reduced fuel consumption offered by a feathered prop may go some way to offsetting the initial cost.

Feathering Propellers

A feathering propeller is a direct replacement for a fixed propeller but with the advantage of less drag when you’re sailing. Once under sail, the prop automatically aligns the blades with the direction of travel, removing the drag caused by a fixed prop. The only disadvantage is that the blades are flat with a constant pitch. This type of propeller is a cheaper alternative to a controllable pitch prop, although with fewer features.

Folding Propellers

If you’re looking for more sailing efficiency, a folding propeller is a common choice. It’s a straightforward design, using the force of the water over the blades to close them flat when sailing. The centrifugal force opens the blades when the prop is turning.

There are some downsides to increased sailing efficiency, though;

– They are only available as fixed pitch propellers.

– Older designs don’t always open with low engine rpm or may only partially open. You may need to rev the engine to open the blades.

– The water pressure may not always be sufficient to push the blades back at low sailing speeds, negating any potential advantage.

– Very poor reverse thrust.

Number of Blades

Older designs were only available with two blades, but nowadays, three and four-blade versions are available. Many of the issues listed above have been addressed with the more modern designs, such as gearing to ensure all the blades open together.

Saildrives are an interesting development with propellers, providing a more compact propulsion system for sailing yachts. Many of the same choices for conventional propeller drive systems apply to saildrives, and you can use all the different propeller types mentioned above.

The primary difference is that the saildrive setup moves the propeller almost directly under the engine, which means the propeller’s angle of attack is parallel to the water’s surface.

Compared to a conventional engine and driveshaft system, these factors will influence the pitch, diameter, and type of propeller you choose.

Sailboat Propeller Issues

Most propellers rotate clockwise when moving forward. Prop walk is the sideways force generated by the spinning propeller, but it’s barely noticeable moving forward.

Going astern is a different prospect, and you can usually feel a distinct movement of the stern to port. You can counter the effect with the rudder, but you can also use it to your advantage when maneuvering.

Propeller design can also contribute to the amount of prop walk you experience.

Cavitation happens when the prop becomes overloaded, and a vacuum forms around the blades. The effect of water rushing into the vacuum creates tiny bubbles, causing a loss of thrust, vibration, and noise. Excessive cavitation can even damage the propeller. Your propeller’s design and the shape of the boat hull can significantly impact how susceptible the propeller is to cavitation, so it is essential to get it right.

Ventilation

Often confused with cavitation, ventilation is the result of the propeller drawing in air. There may be a design fault when propellers sit too close to the surface, but problems can also arise when the propeller spins too fast.

Factors Affecting Your Choice Of Sailboat Propeller

Engine power

It’s crucial to choose the right size prop for your engine. If your propeller is too large or over-propped, then the engine will struggle to reach maximum rpm. When a propeller is too small or under-propped, your engine will rev out too quickly.

When looking at prop size, you must also factor in any gearing in the drivetrain. The gearbox supplies the power output from the engine, so it’s the output shaft torque and power figures that are important.

Hull Resistance

The wet surface of your hull produces resistance, but of course, you also need to factor in any drag caused by extra protrusions on your hull. This will include the rudder, driveshaft brackets, speed sensors, depth sounder, etc. 

Choosing The Right Propeller For You.

Many factors affect your choice of a propeller, and no one solution is better than the other. The first consideration is your motoring requirements, followed by your budget restraints.

If your budget is tight and you only occasionally use the motor, a fixed blade prop is probably your best choice.

Alternatively, a folding or feathering prop could be the best choice if you want to maximize your sailing speed, reducing drag.

When maneuverability is the priority, a feathering prop might be the right choice.

While the options above relate to specific uses, the main characteristics of a propeller are pitch and diameter. These define how the prop will perform and should be the starting point for any propeller choice. Once you determine these basic choices, you can consider more technical factors.

FAQ’s

Is A Bigger Sailboat Propeller Better Than A Small Propeller?

Is bigger better? No, not always, and in the case of propellers, going bigger could cause you all kinds of problems. In terms of size, we’re talking about the diameter of your propeller. A larger diameter propeller will give you more blade area and give you more thrust – in theory.

However, if your propeller is too big, the engine will struggle to turn it and never let it get to its optimum rev range. An oversize propeller will restrict your boat’s performance and increase your overall fuel consumption.

Should You Choose The Highest Pitch Propeller For More Speed?

This is a similar consideration to that of the size (diameter) of your propeller. Increasing the pitch of your propeller blades should, in theory, give you more thrust. As with the diameter, though, too much pitch will limit the performance.

Does A Bigger Propeller Mean Your Boat Will Go Faster?

No, and it may make your boat slower. As we discussed throughout this article, choosing the correct propeller involves numerous factors, and it’s not a simple question of size.

What Factors Should You Consider When Choosing a Propeller?

The first and most important factor is how you sail your boat and how often you use your engine. If you tend to cruise gently, using your engine only when there are light breezes, then low vibration and low cost are possible priorities.

Anyone who enjoys racing will look for speed and low drag, so a folding or feathering prop will be a priority.

Need more advice on buying a sailboat propeller? Get a conversation started on our forum  by leaving a question or comment!

If you found this article helpful, please leave a comment below, share it on social media, and subscribe to our email list., for direct questions and comments, shoot me an email at [email protected].

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July 28, 2022 at 1:24 am

First of all, your first prop size numbers are reversed. In almost all sailboat application propellers the diameter number is larger than the pitch number. 22D x 14P , for example is more along the ratio of diameter to pitch, for the reason of motor H.P. in relation to Tons of boat which you need to propel. The only applications, which are few, where you would run a prop with a higher pitch number than Diameter is when your transmission ratio is aprox. 2 or 2.5 -1, thus a slower turning prop shaft.. l am a prop shop operator in Cancun.. Thank You..

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Why a feathering propeller for my Sailboat?

Published: 12/08/12 at 01:52pm.

Good question. With all of the low drag sailboat propellers on the market today. Why should you buy a feathering propeller?

To be upfront I am jaded. I have been selling Max-Prop feathering propellers for over 27 years. Wow, I still can’t believe I have been at PYI for that long, thanks to Kevin and Frederic for building such a great company. Sorry I digress.

To be simple the advantages of a feathering propeller are threefold.

First, they are positive in their function. The torque of the shaft opens the blades, even if it is encrusted in marine growth it will open. Folding propellers use centrifugal force to open, meaning the shaft has to be rotating before there is enough force to open the blades, this causes quite a lot of shock load to the drive train.

Second, a feathering propeller has amazing reverse. As the blades rotate 180 degrees in ¾ turn of the shaft a feathering propeller has the same efficiency in reverse as in forward. This increase in efficiency decreases prop walk and improves control in reverse. A fixed propeller cuts with the trailing edge and against the cupping on the blades, it loses about 80% of its efficiency in reverse. Similarly, the twist of a folding propeller's blade tries to fold the blades in reverse, presenting a less than efficient attach angle.

Third, a feathering propeller is a low drag propeller. On an average 36 foot boat, a fixed two-blade would create around 70 pounds of pull if it were attached to a scale. A two blade feathering Max-Prop would only create 4 pounds of pull. Quite the difference, think of pulling a 5-gallon bucket behind your boat, that would be a drag.

Cheers, Fred Hutchison

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The only true feathering sailboat propeller

Autoprop Feathering Sailboat Propellers

Autoprop is a sailboat propeller which varies its pitch depending on the operating conditions, to maintain maximum efficiency at all times. The propeller self-pitches based on the hydrodynamic flow at the propeller. It has a higher efficiency over a wider range of rpm settings than any other type of sailboat propeller, so it produces higher speeds throughout your engine’s speed range, allowing lower engine rpm’s, giving greater cruising ranges, fuel economy and quieter cruising. The blades automatically adjust their pitch to match the engine torque to the varying load conditions.

The feathered image on the right shows how, when sailing, Autoprop reduces drag by up to 85% compared with a three blade fixed propeller; with the two blade propeller the reduction can be even greater. This drag reduction can equate to as much as one additional knot in sailing speed.

Motor Sailing

Autoprop automatically varies its pitch depending on engine, wind or sea conditions. The result is maximum efficiency whatever the conditions, with increased sailing speeds at dramatically lower engine rpm giving lower fuel consumption and emissions.

Autoprops unusual blades maximize the thrust delivered whatever rpm the engine is running at. Conventional propellers are designed to provide maximum thrust at the engines maximum output.  Autoprops self feathering provides maximum thrust at all, not a single rpm range.

Maneuvering

In reverse the Autoprop blades swing through 180 degrees and present exactly the same blade shape as they do ahead. The result, the same excellent thrust, with greater stopping power and less prop walk.

Bad Weather

In high winds and choppy seas sailboats struggle to make way. Autoprop allows the engine to to run to a higher maximum rpm delivering more power than any competitor to get you home safely.

Autoprop can use the full power of the engine for towing, or emergencies. The self pitching blades allow full thrust to be developed for extended periods of time without causing overheating or risk to the propulsion system.

Why Autoprop?

All sailboat propellers with the exception of Autoprop are designed to work at one pitch setting.  At this point, normally the maximum engine rpm and hull speed, the sailboat propeller is at peak efficiency.   Do you run your sailboat at full throttle?

Once rpm is reduced to cruising speed, the pitch for the propeller is still set for the maximum value forcing the propeller to work harder to maintain speed; this causes an increase in fuel burn and also an increase in engine emissions. This is how all sailboat propellers work regardless of manufacturer.

Tests on all 4 of the sailboat propeller types found that at 2000 rpm a feathering sailboat propeller was able to propel a test boat at 5.4 knots, but when the same sailboat was fitted with an Autoprop feathering propeller, the boat was able to achieve 6.9 knots for the same rpm and hence fuel consumption.

Autoprop is different.  It balances the rotational forces of the propeller with the forward speed of the boat to automatically set the correct pitch for the correct seaway at every rpm. This will result in cruising speed increases of up to 1 knot or more compared to every other sailboat propeller. There is no other sailboat propeller on the market that does this and this makes Autoprop the perfect motor sailing propeller. Most sailers see typical fuel consumption reduced by 25%, allowing them to sail further for longer.

But Autoprop is not only great under power, once the engine is shutdown, Autoprop can be feathered and it becomes a low drag sailing propeller – the best of both worlds!

Only fully automatic self-pitching propeller on the market

Autoprop has a maximum mid range efficiency of 70% which is higher than all other sailboat propellers – Fixed, Folding or Feathering

Blades are custom airfoil sections and not symmetric sections like all other feathering propellers. This gives significantly improved performance and noise characteristics under power compared to all other feathering propellers

In reverse maneuvers, the blades rotate and give 100% thrust. This gives greater stopping power, greater control, improved handling, almost no prop walk

The Autoprop Range

Autoprop is available in a wide range of sizes and configurations to suit many styles of sailing and sailboats. Typical diameters are from 13″ to 39″ and engine ratings from 10 HP to 350 HP.

Autoprop Service & Support

Fitting, maintaining and servicing an Autoprop could not be easier with the help and guidance of King Propulsion of Virginia Beach, VA.

When you receive your Autoprop it comes fully assembled and pre-greased. Installation on your sailboat is as simple as bolting it on the propeller shaft / saildrive leg, tightening the lock screw and fit the anode. This operation is best completed on the hard or at a short haul. ​ Maintenance is just as simple. Once your sailboat is hauled out and on the hard, ball bearing type Autoprops need a simple cleaning and roller bearing type Autoprops need to be re-greased before winterizing. At this time any eroded anodes are changed and the blades are cleaned and painted in accordance with the maintenance schedule.

Once the blade bearings reach the end of their service life, a service kit is available for each and every Autoprop model along with the necessary tools to complete the service. These kits contain the parts needed to rebuild your propeller back to factory new. As Autoprop doesn’t use gears to pitch the blades like most of our competitors, all the wearing parts are replaceable, vastly extending the life of the propeller. This is a straight forward process that should take a couple of hours per blade. Extensive how too videos are available as well as phone support from our office (East Coast Time), should things go a little pear shaped!

Click the download archive link given below to download the fitting and maintenance instructions for any of the Autoprop models. The files are in PDF format for easy viewing or downloading. Parts to complete any maintenance or repairs can easily be purchased from our online store and ship from Virginia Beach, VA.

Autoprop Sizing & Quote

Find out how Autoprop sailboat propellers can benefit your sailboat by requesting a hassle free no obligation quote. Simply enter the details of your sailboat such as boat type , engine, gearbox ratio and so on in our online web form and we will conduct a power prediction for your vessel to size the right propeller for you. We have currently installed nearly 11,000 Autoprop feathering propellers and counting.

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Ewol propellers make maneuvering easier (reduce inertia) and increase sail speed and optimize engine speed.

EWOL adjustable pitch propellers are made of stainless steel alloys that represent the highest technology in terms of marine corrosion and galvanic corrosion resistance, and are also equipped with the most refined technical solutions that make it unparalleled on the market.

EWOL feathering propellers can be fitted on sailing boats with both traditional (endothermic) and electric engines and with both mechanical and hydraulic inverters. The components of EWOL propellers are made of super-duplex stainless steel alloys, developed by the steel industry for extremely heavy tasks.

EWOL regularly presents new versions of its products with increased performance, and is now also working on developing additional innovative products that will come out in the short and medium term. Nowadays, anyone seeking a truly reliable product that performs over time, solves boat manoeuvrability and sailing speed problems, and is always up at the cutting edge of technology and materials, should install an EWOL propeller on their boat.

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15" Max Prop Easy 3 Blade Propeller - Metric Bores Available, Call For Pricing.

78mm Hub fits shafts 3/4" to 1" and up to 37hp max.

85mm Hub fits shafts 3/4" to 1.125" and up to 47hp max.

90mm Hub fits shafts 3/4" to 1.250" and up to 60hp max.

Vessel data required for order. Click here to submit information.

• The Max-Prop Easy is a true step forward in Max-Prop design. The ease of installation and simple pitch adjustment make this model a great choice for a wide range of boats. The three blade design provides smooth and efficient power.
• The Easy ships fully assembled, making installation similar to a fixed propeller, basically slide it onto the shaft, nut it in place and the propeller is ready to go.
• As with all Max-Prop’s the Easy pitch is adjustable. With the Easy the pitch is adjustable in 2 degree increments, providing the ability to fine tune the loading of the engine. In addition, the pitch can be set for different levels in forward and reverse, giving you the fine control we've been missing in reverse.  Moreover, pitch adjustment can be done in the water as the propeller does not need to be disassembled to change the pitch.

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