sailboat propeller test

7 Best Sailboat Propellers

If you own a boat, it's very likely that it has a propeller that you can use when you don't want to jib, tack, or hoist the sails. As such, having the right propeller for your sailboat that is extremely efficient under power, while not slowing you down under sail is important. This is why you have to choose the best sailboat propeller for your vessel.

Having the right sailboat propeller that properly fits your boat is one of the most essential things if you want to get the most out of your vessel. When it comes to boat propellers, there's no one-size-fits-all. In most cases, the factory-installed model may not be the best for your boat, so installing an after-market model would be the best way to go, especially if you want to improve your boat's acceleration and top speed.

One of the main duties of a sailboat propeller is to ensure or determine how fast your boat can go. It plays an integral role in enhancing efficiency and improving the boat's handling capabilities. So whether you're planning to set sail or just cruise around, having the best propeller for your boat is of immense importance in enhancing your boating experience.

Whether you're in the market because your boat's current propeller is damaged or you're just looking for a new propeller to improve the performance and efficiency of your boat, you've come to the right place. In this comprehensive guide, we'll help you filter through an ocean of choices and find a perfect propeller that matches the needs of your boat. At the end of this read, it should be quite easy to pick a propeller that makes and keeps your boat running and operating at peak efficiency.

Table of contents

How to Choose the Best Boat Propeller

A propeller is a crucial component of any boat. Without it, you may be forced to only rely on your sails or even row the boat manually. Even though they may all seem the same, these propellers have various features that make them different. So if you're in the market for a boat, here are how to choose the best boat propeller.

Generally, we often use our boats at sea level but there are those occasions when you may have to cruise at higher altitudes. For example, you may want to boat in a mountainous region and this means less oxygen. This means that your boat cannot produce the amount of power as it would in an oxygen-rich environment.

So if you plan to sail at an elevation, you can choose a propeller with a lower pitch as it will deliver more power.

Boat propellers are mainly made from three main materials including aluminum, stainless steel, and plastic. Stainless steel is an ideal choice if you're looking for strength, durability, and performance. In terms of aluminum, you'll get excellent performance, lighter design, and are more affordable. A propeller made from plastic is perfect for small boats but they may not offer the same durability and power as metallic propellers.

A propeller's weight can have significant effects on the performance of your boat. A heavier propeller will require less pitch and your boat's engine might not work at its full capacity. This is why it is of great importance to consider the load or weight of a propeller as well as the load that your boat will be carrying so that you can choose a prop with the right pitch and diameter. You should, therefore, buy two propellers with different pitches so that they can be used interchangeably depending on the circumstance.

Ventilation

Needless to say, a propeller will not function at full capacity without proper ventilation. If a model isn't properly ventilated, the surface air might be pushed into the blades or the propeller, thereby leading to below-par performance. This is why you should ensure that the propeller is properly installed within the lower part of the transom and should be able to work even in very harsh conditions.

When it comes to choosing the right size of a propeller, you'll have to ensure that the diameter of the prop is twice the distance from the hub center to the blade's tip. A propeller with a larger diameter can perfectly accommodate a larger engine. You should also consider the prop's pitch, which is the distance the propeller will travel in one rotation. The pitch is comparable to a car's gear and sometimes you may need low pitches for the boat to move.

Cavitation refers to a situation whereby water vaporizes because there's a lack of pressure on the prop's blades. This low pressure and vaporization can lead to terrible consequences and can lead to erosion of the material. Such issues can be caused by poor polishing, poor design, and other flaws in the blade. This is why you should go for a high-quality propeller to ensure that cavitation doesn't become an issue.

Whether you go for a three-blade or four-blade propeller, they all work great. You, however, have to keep in mind that a three-blade prop offers top performance and speed while a four-blade prop is perfect for difficult conditions, especially when speed isn't a priority. Again a four-blade prop is great in fuel efficiency but may reduce your boat's rpm.

Best Sailboat Propellers

Here are the 7 best propellers currently available in the market.

Mercury Marine Spitfire

If you've held a little interest in boat propellers, you've probably been part of the debate between three-blade and four-blade propellers. While it may be difficult to conclusively choose the best type of propeller based on the number of blades, the Mercury Marine Spitfire puts an end to this debate. This is because it offers the best of both worlds and remains one of the few propellers that are compatible with various motors.

This propeller is designed to be the ultimate prop for a wide range of outboard boats in terms of offering outstanding performance. This aluminum prop is designed with four blades and a long barrel that combine to give it an additional stern lift and lightning-fast holeshot, which is crucial in skinny-water applications. To put it into perspective, this prop can offer 25% faster acceleration and superior holding without necessarily compromising on top speed.

This is a unique boat propeller that is magnificently designed to cater to the unique demands of various boats. Whether you're using an outboard boat with 25hp or 125hp, this prop can spin up quite fast and improve your boat's acceleration thanks to its innovative designs.

• ‍ Offers aggressive blade cupping
• It is quiet as it comes with a noise-reducing hub
• Doesn't have blowouts on hard turns
• ‍ Quite expensive

Quicksilver Nemesis 4-Blade Boat Propeller

Featuring arguably the most aggressive geometry of all aluminum props, the Quicksilver Nemesis 4-blade Propeller offers the best cup in terms of acceleration, holding, and tenacity when gripping in turns. The fact that it is designed with a high-rake and reduced diameter makes it incredible if you're looking for a prop that can help your boat maintain top speed.

This is a prop that's helping rewrite the engineering rules as you get top acceleration and tenacious holding without compromising on top speed. This is great for any boat that's powered by stern drives ranging from 25HP to 250HP and will significantly augment the performance of your boat.

If you've been looking for an all-round prop, this is the best option. It will never let you down when it comes to delivering a superb holeshot, fuel efficiency, incredible control and comfort, and top speed. Better still, you don't have to break the bank to acquire one.

• ‍ Offers 3-blade speed with 4-blade performance
• A great and powerful prop for rough waters and water sports
• Offers impeccable quality and performance and a fair price
• Available in a wide range of pitches and diameters to suit different motors and needs
• ‍ Might not be ideal if you want a left-hand rotation

Turning Point Hustler Propeller

If you're in the market for a prop that incorporates in its design some of the newest and most efficient features, then the Turning Point Hustler Propeller can be a superb option. This is a high-performance 4-blade stainless steel propeller that comes with a guarantee that it will be devoid of air bubbles and any other defect that could negatively impact on its performance or that of your boat.

This prop's blade design is structured with one of the best high rake patterns, aggressive cupping, fine-tuned pitch aggression, sharp trailing edges; all to ensure that your boat achieves top speed, maximum acceleration, fuel efficiency, and top-end performance. This prop is designed to be long-lasting thanks to its five-step, powder-coated finish.

The Hustler is designed with a squeeze cast for added strength and a high flow-through barrel exhaust system to increase horsepower while offering top-end speed.

• ‍ Enhanced low consumption and fuel efficiency
• Quite affordable
• Offers improved handling
• One of the most advanced props in terms of technology
• ‍ May interfere with the boat's rpm

Young Marine OEM Grade Aluminum Outboard Boat Propeller

Whether you're on a tight budget or just looking for a quality OEM grade propeller that will offer top performance, the Young Marine OEM Grade propeller can be an ideal option. This propeller is meant for Mercury outboard engines and will cost half the price of other top brands while offering the same if not much better results in terms of quality and performance.

The Young Marine is available in a wide range of pitches and diameters. This not only makes it one of the most versatile props in the game but offers you the flexibility of going for something that perfectly and exactly suits your size and pitch needs. The fact that the diameters and pitches are the same as the original OEM propellers makes installation a lot easier while still offering top performance.

This propeller is made from the highest-quality aluminum, thereby offering an incredible combination of strength and lightness. It's perfectly suited for Mercury outboard engines and works great within a range of 25HP to 75HP.

• ‍ Affordable and offers excellent value for money
• Offers a wide range of diameters and pitches
• The 3-blade design offers improved performance
• ‍ Only works best for an engine with HP ranging from 25 to 75

MotorGuide 3-Blade Machete III Boat Propeller

Designed with 3-blade superiority, MotorGuide Machete 3 is a superb boat propeller that can be of great help if you're planning to sail over skinny water full of seaweed and other aquatic flora. Featuring a prop pint and prop nut, this is an impressive boat prop that's designed to offer efficiency and top speed.

It performs relatively well across various voltages including 12, 24, and 36 voltages. This prop is specifically designed for trolling motors and can easily outperform similar props in this category.

• ‍ Great for trolling motors
• Offers fast and efficient performance
• Works great across a wide range of volts ‍
• ‍ It's affordable
• The tapered hub design is excellent
• ‍ The blades are made of plastic and their durability is questionable

Mercury Max Black Boat Propeller

This is another Mercury propeller model that's widely known in the industry for offering top performance and speed. It's designed with several amazing features such as the combination of a small pitch and a bigger diameter to enhance its efficiency. It is also created using premium aluminum to offer a great balance between strength and lightness.

It comes with the standard 3-blade model to enhance speed and an outstanding hub system that is high-rated by users. This is one of the best-selling 3-blade propellers in the world and will deliver uncompromising performance in virtually every situation. Its geometry may seem conservative but it will never lose even the slightest bite on the water even when your boat is making the modest of turns.

• ‍ Its design is efficient
• Made of premium aluminum material
• Works great in almost any situation
• Can reach top speed in less than 50 mph
• Comes with a flo-torq hub kit
• ‍ Noticeably slower than many stainless steel boat props

Michigan Wheel MICH 3 Blade Boat Propeller

If you have a smaller boat but want a quicker and smoother cruising, the Michigan MICH can be your best bet. Featuring 19 prop pitch and a 14.5 diameter, this 3-blade prop delivers consistently great performance and can be easily customized for various types of boats.

Installing this propeller is quite easy and it will hold up well for many years to come with minimal maintenance. The blades are made of premium aluminum and are coated in black to prevent it from corroding. This can be an excellent option if you're looking for a superb prop for a small boat.

• ‍ It is corrosion-resistant ‍
• ‍ Installing it is easy
• Offers top speed and makes cruising quite smooth
• It can be customized to fit well in a wide range of boats
• ‍ Not perfect for bigger boats

To this end, we hope that you are now more informed when it comes to choosing the best propeller for your boat. Of course, a propeller is of great importance to your boat and will increase your vessel's efficiency. You certainly do not want to spoil your boating experience just because you chose a low-quality propeller and that's exactly why you should go for a prop that perfectly suits your boat.

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Daniel Wade

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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Understanding Your Sailboat Propellers

• By Michael Cilenti
• Updated: July 6, 2015

Out of sight and out of mind, sailboat propellers are often an afterthought for cruising sailors. Ironically, because manufacturers have developed a variety of efficient sailboat propellers designed to maximize thrust under power while minimizing drag under sail, selecting the right prop for a sailboat can be even more complex than it is for a power vessel. In order to make an informed decision and choose the right propeller for your needs, it’s important to understand the advantages and disadvantages of all the options available.

Propeller Geometry

Before delving into specific types of sailboat propellers, in order to grasp how all the design elements work together, it’s ­important to understand the basics of propeller geometry. All propellers — from sailboats to power cruisers, outboards to aircraft carriers — share the following characteristics.

To start, the hub is the central part of the propeller, to which its blades are attached either as a single casting or mechanically; it, in turn, is connected to the propeller shaft in traditional drive trains, or to the saildrive , which has become more and more prevalent in contemporary cruising boats. Regarding those blades, the leading edge is just that: the edge that leads into the water when turning ahead. (It’s also the edge closest to the forward part of the propeller hub.) The trailing edge , conversely, is the opposite edge of the blade (the one closest to you when standing on the aft side of the prop).

The root is the inboard side of the blade and forms the transition where the blade connects to the hub, while the tip is the outboard edge of the propeller blade. The blade face is also known as the pressure side, and is the side that faces aft. The blade back is also known as the suction side, and is the side that faces forward.

The majority of propellers are right-handed ; viewed from astern, they rotate clockwise when moving forward, and have a slight tendency to swing the stern to starboard. Since the propeller is designed to be most efficient when going ahead (the direction one travels the vast majority of the time), this side force is minimal. When going astern, however, the opposite is true, and the stern will “walk” to port, which is usually the more pronounced of the two side forces and can therefore be a distinct advantage, or disadvantage, when maneuvering in close quarters. Prop walk is dependent on several factors, including hull shape, but also the propeller itself. An inefficient propeller will introduce more prop walk than an efficient one.

Diameter and pitch are two of the most basic dimensions used to describe a propeller. If you were to attach a pencil to the tip of one of the blades and ­rotate the propeller one full turn, tracing a circle, the distance across this circle would be the diameter of the propeller. Next, if you were to rotate the propeller one full revolution in a solid medium that does not slip (think of a screw in wood), the pitch would be the forward distance that the propeller would travel in that single revolution. With modestly sized yacht propellers, diameter and pitch are routinely measured in inches (as opposed to feet or meters for ship propellers). So a 12-by-20 prop has a 12-inch diameter and a 20-inch pitch.

Given the definition of pitch, you might wonder why you wouldn’t choose a propeller with higher pitch in order to gain additional power. But propellers must be sized in relation to the rest of the propulsion system, and must match the power curve of the engine, as well as the rpm range afforded by the reduction gear. As such, a propeller with ­excessive pitch may not actually generate additional thrust, since it would overload the engine and prevent it from reaching the designed rpm, which can reduce fuel efficiency and increase wear to critical engine components. ­Additionally, an overloaded propeller is susceptible to cavitation , which happens when a prop rotates and creates a partial vacuum. Water rushes in to fill that vacuum, creating tiny bubbles; when they collapse, they basically pound the prop. While cavitation will occur in small amounts in very localized areas on almost every propeller, excessive cavitation will result in a loss of thrust, excessive noise, and vibration, and can be violent enough to actually pit or erode the propeller.

Many blades also have rake and skew . Rake is the forward or aft slant of the blades when viewed from the side. Propellers are generally given some degree of aft rake to help increase efficiency while decreasing vibration. In fact, many propellers on outboard engines exhibit a significant amount of aft rake. A propeller blade is skewed if it is asymmetrical with respect to a straight radial line drawn outward from the hub. Skew helps reduce pressure fluctuation and therefore vibration and noise.

As an example, think of those classic World War II films, when the submariners would huddle together, waiting for the next depth-charge attack while listening to the pulsating sound of the destroyer’s propellers as it passed overhead. That distinct pulsation was caused by the difference in pressure as each propeller blade passed close to the ship’s hull. Even if the propeller blades were equidistant from the hull on all sides (think of a propeller in a tunnel or nozzle), the pressure difference between the propeller tip closest to the surface and the tip that is deepest can be substantial enough, especially in larger propellers, to cause similar pulsation. The prop on a modern submarine is an example of a highly skewed propeller; the sickle-shaped blades are designed to reduce noise and vibration to an absolute minimum, even at the expense of propulsive efficiency.

The number of blades can also play a significant role in the propeller’s performance. As with skew, at least in theory, a greater number of blades will generally reduce vibration, since for a given rpm there is less time between each blade passing a given fixed point. That said, if a propeller is well designed and dynamically balanced, a two-bladed prop will not vibrate more than a three- or four-bladed prop. However, in instances where a shaft is slightly out of alignment, a three-blade prop could help decrease shaft vibrations.

Along these lines, if a propeller had an infinite number of blades — if it were a solid disc — there would be no vibration. Additionally, a propeller with more blades will generally have a larger expanded area than one with fewer blades, although that is not necessarily always the case. Expanded area is essentially the total area of the blades. For a given horsepower, a larger expanded area will result in lower thrust loading, or conversely, a propeller with a larger expanded area can absorb more power prior to experiencing significant cavitation. At the end of the day, it’s a delicate balance between optimum blade area and the potential for excessive diameter. Wide diameter causes excessive tip speed, which results in cavitation.

Propeller Options

There are several propeller types available for auxiliary sailboat applications. To begin, let’s look at some basic but often confused definitions for different types of propellers.

Blades may have constant or variable pitch. A propeller with constant pitch has blades whose pitch, or angle of attack, remains the same from the root to the tip. Conversely, a variable-pitch propeller has blades that appear twisted; that is, the blades will have greater pitch at the root and less pitch at the tip.

While constant-pitch propellers are easier and therefore cheaper to manufacture, variable-pitch blades are more efficient. Consider each blade’s motion as the propeller spins. At a given rpm, the part of the blade near the root is moving much slower than the part near the tip. If this seems confusing, think about the change in circumference as we move outboard on each blade; a point closer to the hub has less distance to travel to complete a full circle than does the tip of the blade. Since they both must complete the revolution at the same time — they are, after all, two points on the same blade — the point near the tip must move faster than the point near the root. Now, we also know that the faster the blade moves, the more thrust it will produce. So, in order to maintain constant thrust along the entire blade, the pitch is reduced as we move farther out toward the tip.

Propellers may also have either fixed pitch or controllable pitch . Fixed props are available in a wide range of diameters and pitches. All fixed props have twisted blades, but as the name suggests, they can’t be adjusted. Feathering props, alternatively, have flat blades with no twist. This makes the blade area relatively inefficient, but that drawback is offset by the ability to adjust the blades’ pitch.

A controllable-pitch propeller also has the ability to change the pitch of the prop blades, by rotating each blade at the root, but these props are generally used on superyachts, not your normal cruising boat. On these larger vessels and ships, controllable-pitch propellers are used to keep the engine operating in the most efficient rpm band by varying the pitch of the propeller to change its thrust rather than the speed of the engine.

Additionally, many controllable-pitch propellers also have reversible pitch: In order to provide astern thrust, the pitch of the propeller blades is reversed while the propeller continues to spin in the same direction. For larger ships, this has some distinct advantages, as it eliminates the need to stop the propeller before turning it in the other direction. This simplifies the machinery required and dramatically reduces the time before reverse thrust is produced, therefore increasing maneuverability. For sailing vessels, in addition to the advantages previously described, controllable-pitch propellers can often “feather” the blades to minimize drag while sailing.

Controllable-pitch props can also be adjusted to maximize the power and efficiency of your particular propulsion system and boat, something that fixed-pitch propellers cannot do. This ability to fine-tune the propeller — coupled with advanced blade designs in controllable-pitch props — may promote a notable increase in power, speed and efficiency. It’s important to note, however, that compared to fixed-pitch models, these controllable-pitch benefits do come at increased cost. Cost aside, the complexity of the system also may make it more prone to issues than a fixed-pitch propeller, and more difficult to find parts and complete repairs when voyaging in remote regions.

Of course, many sailors are familiar with folding propellers, which are fixed-pitch models designed to fold back in order to minimize drag while under sail. Like fixed props, these come in a wide variety of diameters and pitches, have twisted blades, and aren’t adjustable. Originally, folding props were generally two-bladed, but three-bladed props are now widely used and very popular, and four-bladed models are also available. Folding props are designed so the centrifugal force of the spinning shaft will cause the blades to unfold when the engine is engaged. Folding propellers are less complicated than their controllable-pitch cousins, but compared to standard fixed props, they still offer reduced drag under sail. When folded, they are also less prone to being fouled by seaweed or other debris than a feathered, controllable-pitch propeller.

In days gone by, many folding propellers got bad raps for several reasons. They wouldn’t open immediately at low rpm, particularly in reverse, or they required a revved engine to provide the sufficient centrifugal force to open them. Conversely, at low speeds while under sail, the flow of water was sometimes insufficient to keep the blades folded, particularly if the prop blades were aligned top to bottom (where gravity could open the bottom blade) rather than side to side.

When we raced sailboats when I was younger, we used to dive down and put a rubber band around the folded prop once we got out to the racecourse. Or we’d make a mark on the propeller shaft with paint or a permanent marker when the boat was on the hard; we could then position the shaft so the blades were aligned side to side once we secured the engine. However, those issues have largely been eliminated with today’s modern, highly engineered folding props. These days, the blades in most folding props are geared and synchronized, and very efficient in all conditions, whether under sail or motoring. Their reliability is underscored by the fact that they’re now standard equipment on new boats from Beneteau, Dehler, Gunboat, Hanse, J-Boats, Jeanneau, Morris and many other manufacturers.

The variety of propellers available today provides a wide range of options for sailors to choose from. The advantages and disadvantages of each propeller type must be weighed against your sailing and motoring style. When investigating a new prop, shop wisely and ask lots of questions of the specific manufacturers; it’s important to get personalized recommendations for your boat and your plans. Understand the differences to ensure you find the best fit for your needs.

Propeller Resources:

The following is a list of propeller manufacturers and their websites.

• Autoprop Automatic Variable-Pitch Propellers
• Flexofold Folding Propellers
• Gori Folding Propellers
• J Prop Feathering Propellers
• Kiwiprop Feathering Propellers
• Max-Prop Feathering Propellers
• Martec, Autostream and Slipstream Folding and Feathering Propellers
• Variprop and Variprofile Feathering Propellers
• Volvo Penta Folding Propellers

A graduate of the U.S. Coast Guard Academy, where he raced inshore on the varsity sailing squad and offshore to Bermuda and Halifax, Lt. Cdr. Michael Cilenti is currently second-in-command of the Coast Guard cutter Waesche out of Alameda, California .

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The Ultimate Propeller Test – 10 things to know

Back in 2009 the Yachting Monthly Magazine carried out a detailed test to compare all the latest low drag propellers available on the market and the Ultimate Propeller Test is still the go to reference for many who are looking to upgrade their propeller and sail faster!

The propellers on test included:-

• AUTOPROP – H5-394mm
• AUTOSTREAM THREE-BLADE – 17x11in
• AXIOM THREE-BLADE – 16x11in
• FEATHERSTREAM THREE-BLADE – 16x11in
• FLEXOFOLD THREE-BLADE – 16x11in
• FLEXOFOLD TWO-BLADE – 16x13in
• GORI THREE-BLADE – 15in
• KIWI PROP THREE-BLADE – 16x11in
• MAX PROP THREE-BLADE – 16x11in
• MAX PROP TWO-BLADE – 16x12in
• SLIPSTREAM THREE-BLADE – 15.5x11in
• SLIPSTREAM TWO-BLADE – 16×11½in
• VARIFOLD TWO-BLADE – 15x11in
• VARIPROFILE THREE-BLADE – 16x11in

This was an interesting test which to a large extent proved what was widely known with a few surprises!

Here are 10 things to know about the Ultimate Propeller Test…

• Maximum Hull Speed . This test was carried out in flat calm water with virtually no wind so 2B folding or fixed propellers excelled due to less interference between blades. However, when resistance on the yacht increases a propeller with more surface area (3B or 4B) will continue to drive the hull efficiently and be more consistent through the water where a 2B propeller will lose out.
• An efficient and well-designed folding propeller will offer the best forward driving hull speed in flat calm conditions but not so efficient in astern. Flexofold propellers did very well.
• Stopping Time . The value of this test in an emergency is obvious. Most feathering propellers like the FeatherStream benefit from efficient blade angles in astern and all showed good stopping power, better than the fixed and folding props.
• Prop walk. This part of the test is misleading! It appears to show that folding props produce less prop walk than feathering ones. In practice the opposite is true. This is because the test was done at full throttle in reverse. Feathering propellers work much better than folding propellers at low throttle in reverse. The whole idea of a feathering propeller is that is does not need to be revved hard in reverse. It will produce a lot of thrust at very modest throttle, where Folding propellers have to be operated at high throttle in reverse (relying on centrifugal force) and the result is more prop walk at these high shaft speeds. It would have been better to do the same test but at a slower shaft speed.
• This test was performed on a Beneteau Oceanis 323 . Your hull form and installation may be very different so the results from this test are focused on this yacht only , different hull forms and installations will require very different propellers, so propeller choice is specific to your boat and your requirements.
• All folding and feathering propellers offer a significant improvement in sailing performance due to reduced drag.
• Pitch adjustability! Not all propellers tested can be adjusted for pitch. Feathering propellers such as FeatherStream can be adjusted to fine tune engine loadings which can influence cruising hull speeds for more efficient motoring.
• No propeller is perfect in every aspect! Some excel in certain areas but are less effective in others. Expect a level of compromise when choosing your propeller.
• Yacht owners have individual priorities regarding propeller performance. The propeller designer/supplier must identify each individual owners’ priorities and offer the propeller which most closely matches these requirements. Low drag propellers are tailor made not only for each hull form, engine, gearbox and shaft but also for each owner. We don’t always want the same thing!
• You generally get what you pay for! Folding propellers are the exception. The most expensive 2B propeller (Gori) was outperformed in all tests by the less expensive Flexofold propeller, whilst the most expensive 3B propeller (Gori) trailed in all the most crucial tests. Of all the feathering propellers the FeatherStream offers the best value for money!

So there you have it, these are just a few pointers highlighting aspects of the test which will help you understand some of the performance outcomes.

Read the original propeller test report

You can read the original “ Ultimate Propeller Test by Yachting Monthly ” here or download a PDF version .

Contact us if you have any questions about your boat or you wish to talk to us about anything propeller related

Posted on Thursday, October 24th, 2019

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• Systems & Propulsion

Folding vs. Feathering Props

With a new engine, mahina tiare gets a new streamlined screw..

For the past 40 years we’ve sailed an average of 10,000 miles annually between Australia, Alaska, Antarctica and Spitsbergen motoring or motorsailing between 400 and 600 hours, depending on the area – more hours in high latitudes of Antarctica and the Arctic, fewer in the tropical trade winds.

Our HR 42 came with a fixed three-blade prop which served us well when pushing bergy bits out of the way in Patagonia, Antarctica and Alaska, but obviously slowed us down in light airs. When we had our current Hallberg-Rassy 46 built in 1996, anticipating better sailing performance, we opted to install a Max-Prop as that was acknowledged as the best option at that time.

Max-Prop has been around since the early 70s and is a proven design, but after 18 years and 190,000 miles of use, we had the prop rebuilt three times, each time costing between $800 and $1,200. The first time the prop was rebuilt by Henleys, an Auckland prop shop, and the other two times by PYI, the U.S. importer/distributor located near Seattle. I was told that the rebuild included brazing more bronze on to the props inside working surfaces followed by machining the built-up surfaces down to original tolerances. When I enquired what I could do to extend the period of time between rebuilds, PYI said, More grease! So for 15 years, we not only greased the prop before launching at the start of our season, but also mid-season going underwater with mask, fins and grease gun to do so.

The advantages of the Max-Prop are very little drag when sailing as the prop instantly feathers unless the engine is engaged, no freewheeling in neutral, adjustable pitch, and incredible stopping power in reverse. Max-Prop can literally bring a boat from 6 knots to a dead stop in a boat length. This feature has kept us from nailing coral heads at least twice. The ability to adjust the pitch to maximum engine efficiency improves fuel economy and the newer Easy model Max-Props can be adjusted in the water without having to disassemble and reassemble the propeller, which is a substantial improvement over the earlier Classic version. We did encounter (and frequently use to our advantage) fairly substantial propwalk.

The disadvantages are that when the Max-Props feathers, the blades are still open and prone to fouling lines and kelp. During our 2008 Atlantic crossing we had to get in the water with mask and fins three times to remove cargo nets and large 3-inch floating lines from the prop. The Atlantic Ocean has a garbage gyre similar to, but smaller than the Pacific Garbage Patch, and we must have found the edge of it during our 2008 crossing. Last month, we completed the identical route from the Canary Islands to Antigua with only one sighting of trash and favorable winds that allowed us to basically sail the rhumbline. As a funny side note we were once making landfall at Fastnet Rock when a smaller boat passed us under sail. Trim as we might, we couldn’t catch them and only when they were several boat lengths ahead did Amanda think to check astern only to discover a fat turquoise rope trailing behind. The rope, obviously was not ours, was caught on the prop and we wondered how long it had been there as we’d not used the motor for several days.

During a 2015-2016 winter refit in Sweden, after reading the results of two European propeller efficiency tests and after speaking with several owners who had switched from Max-Prop to Flexofold, I had a Flexofold prop installed. Jack Skrydstrup, Flexofolds Danish manufacturer recommended the size and pitch, and the boatyard installed it without problems.

In comparison the stopping power is not nearly as good as with the Max-Prop, and the prop freewheels when the engine is shut down in neutral. Weve found that shutting down in slow forward solves the freewheeling issue. Strong on the Flexofolds plus side are blades that feather aft, instead of extended, so they’re less likely to snag lines or kelp. We notice almost no propwalk in reverse. In addition, cost of ownership is reduced as there doesn’t appear to be a need to rebuild and there are considerably fewer spare parts to carry.

However, the improvements in efficiency are difficult to quantify as we also repowered at the same time, switching from a 95 hp. to 75 hp. engine, but our top speed rose 0.7 knots, and fuel consumption on an identical Atlantic crossing dropped from 1.33 gph to .83 gph.

On the service side, PYI, the U.S. importer/distributor of Max-Prop is renowned for their customer service, doing a superb job of shipping spare parts immediately and quickly handling rebuilds from their shop near Seattle. Flexofolds Jack Skrydstrup is helpful, and ships quickly, although shipping is factory-direct from Denmark. Ive only heard one incident of an owner needing parts during European summer vacation period when shipping was delayed slightly.

Amanda and John Neal spend seven months at sea sailing 10,000 miles a year while leading sailing training expeditions. The have more than 500,000 sea miles combined experience.

Nigel Calder, author of The Boatowners Mechanical and Electrical Manual shared propeller data collected during the course of his recent hybrid propulsion experiments. Here’s his summary: “We tested Flexofold, three Goris, two Volvo-Penta four–blade folding props, three Brunton Autoprops, a Brunton Varifold, and a fixed pitch, which was undersized so not a fair comparison – it just happened to be available. The objective of these tests was to collect baseline data for other purposes. As such, the propellers were not necessarily properly matched to the boat and these are not apples-to-apples comparisons. “The Flexofold, Volvo-Pentas and Varifold had similar efficiencies, but from an engineering perspective the Flexofold was the simplest design and easiest to fit.”

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Our experience with Flexofold is that they have not stood behind their size / pitch recommendation. Great prop otherwise — well made and much more efficient than our Max Prop.

I am considering installing a Brunton Autoprop on my 34’ Vashon cutter (26’ LOD), 6500# displacement. Has anyone had experience with these props and/or what is your opinion of installing this type of feathering prop?

It would be helpful if you labeled the pictures so that us less knowledgeable sailors knew what prop we were looking at. Very good overview article considering all of the variables involved. It provided some insight. By way of an example, I tried 3 different props on my dingy before I found the best fit for my needs; a boat is more complicated.

I absolutely love the concept of the Autoprop. After having held one at a boat show, and seeing a cutaway model, I still can’t figure out how it works, but that doesn’t stop it from being brilliant. Alas, when we re-propped our Marshall 22 catboat, there wasn’t enough room for any of the Autoprop line.

We chose a 12″ three-bladed Featherstream and are very happy with it. On the downside, you have to remove a pitch “cassette” (a specifically-sized arc of metal) and replace it with a different size in order to change the pitch. But on the upside, man is that simple. You don’t even have to fully-disassemble the prop to do it. A fellow at the boatyard watched wistfully as he talked about having to disassemble is feathering prop and try to figure out which detent a screw would fit into when covered with grease.

The price was also quite reasonable, and service from Canada has been great.

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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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Reader Interactions

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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Choosing the Right Boat Propeller

• By Boating Staff
• Updated: August 25, 2017

Choosing the Right Prop

During my 30-plus-year history with this magazine, reader queries about propellers have remained constant and unrelenting. Questions that once came in letters and phone calls now arrive digitally, but they are the same questions: Should I switch from an aluminum prop to one made of stainless steel? Will a four-blade boat propeller improve my hole shot? My buddy says my prop is too small/big. … What do you think? And the ever-popular Will this prop make my boat go faster?

So it’s useful to offer another installment of prop basics, an attempt to answer these most elemental and popular propeller head-scratchers, this time using an outboard-powered fishing boat and a selection of props from the vast inventory of Mercury Marine. From its Oshkosh, Wisconsin, testing facility Merc offered us the use of a 1,900-pound Key West 2020 center-console rigged with a Mercury 150 FourStroke outboard, and a full complement of data acquisition gear. From the site’s “wall of props” we chose six Mercury propellers to test, and then bundled up on an October morning and motored out to Lake Butte des Morts. We tested each boat propeller “light” (just the tech on board) and “heavy” (with 350 additional pounds in the boat), always with the 60-gallon fuel tank full.

The three-blade aluminum Black Max is the best-selling propeller in the world. It’s standard-issue from boatbuilders paired with the MerCruiser Alpha sterndrive and outboards up to about 135 hp. The Black Max is a generalist, with conservative geometry, designed to deliver acceptable performance in almost any situation. Blade flex and modest cupping cause the Black Max to slip more than most stainless-steel props. In our testing, it was significantly slower than the stainless-steel props but matched the acceleration of much more expensive options. The Black Max does not produce the lift of a stainless-steel prop. When running the Black Max, I noted that spray was breaking off the hull forward of a gunwale rod holder, while it broke 18 inches abaft the same rod holder with every stainless prop we tested. I had to trim down to keep the prop from losing bite on the water even when making modest turns — and it blows out immediately when over-trimmed. Made of aluminum, it’s easy to ding up, even beyond repair, with a bottom strike.

Tempest Plus

To move up to stainless steel, we chose the Tempest Plus, a performance three-blade boat propeller designed to produce good top speed and a popular choice with tournament bass and walleye anglers. The 17-pitch model we tested is actually the smallest pitch offered — a fast bass boat will run a 25-pitch Tempest Plus. To boost speed, the Tempest Plus has aggressive rake to promote bow lift and less blade area to reduce drag. All of those design elements are critical to maximizing performance on an 80 mph bass rig but become less impactful as boat speed slows down. In our testing, I noted that the Tempest seemed to take less trim than the other stainless props and produced a little less lift. But the boat felt really planted and steady in the water and handled well. The Tempest will also be much more durable than an aluminum prop.

Revolution 4

If three blades are good, will four be better? To find out we ran the Revolution 4, sort of a four-blade cousin to the Tempest Plus designed to deliver better hole-shot acceleration than the Tempest simply because it has more blade area. The Rev 4 is very popular on twin-rig outboard offshore boats because it ­really holds well in rough water, especially in following seas that can lift the transom and ventilate the prop. Merc also recommends the Rev 4 for stepped-hull boats, which send a lot of frothy, aerated water to the props. The extra blade should also produce more drag and thus lower top speed. That might be true on a faster or heavier boat, but in a more modestly powered rig like ours, the difference in performance between these two props is negligible. That said, the Rev 4 feels great from the helm. There’s pronounced bow lift at the last 5 percent of the trim range, it holds well in turns, and it offers better reverse thrust than the Tempest Plus. For general-use boating, overall smoothness is the key advantage of a four-blade prop.

Enertia 14 7/8″ x 16″

We ran Enertia to try a different-style prop and also to demonstrate the effect of changing prop pitch. The Enertia is offered in 1-inch pitch increments, rather than the traditional 2-inch increments, to really fine-tune top rpm. It replaced the venerable Mirage Plus as the go-to Verado prop for heavier offshore fishing boats. The smaller diameter helps the motor spin up faster for better acceleration, and the increased blade area works especially well for heavier boats with a single motor. Mercury says the Enertia likes to run deep in the water, and so it’s also a good fit on sterndrive runabouts and big pontoon boats. Comparing the three Enertia pitch sizes we tested, we can generally say the 16-pitch choice produced better acceleration but lower top speed, while the 18 delivered the best top speed and worst hole shot. You’d see similar results comparing props with 2-inch pitch increments, but it would be more pronounced.

Enertia 14 5/8″ x 17

The reason the Enertia propeller is offered in 1-inch pitch increments is because it was designed specifically for Mercury Verado outboards. The 5,800 to 6,200 peak rpm range of Verado outboards both is higher and occurs in a narrower band than two-stroke outboards, such as the Mercury Optimax, which has a peak operating range of between 5,000 and 5,750 rpm. Since prop pitch is essentially the final drive gear ratio for an outboard, smaller pitch increments allow adjusting top rpm to suit load conditions for engines with narrower top rpm bands.

The 17-inch-pitch Enertia propeller proved just right for our test boat. First, it allowed the engine to “turn up” to its maximum rated rpm. (That the engine slightly exceeded the recommended rpm range while lightly loaded with this prop is acceptable and, in fact, what we look for when testing boats. In “normal” use, most boats are loaded heavier, have the bottom painted, carry more crew, etc., all of which brings rpm down.) It also matched the top speed of the 18-pitch prop and the hole-shot acceleration of the 16-inch prop.

Enertia 14 1/2″ x 18

The 18-inch-pitch Enertia propeller delivered the best top speed and the worst hole shot. It’s expected that more pitch will equate to higher speed, since pitch is the nominal distance the propeller moves through the water for each revolution. Ergo, for the same amount of rpm, more pitch equals more speed, which our testing confirmed.

But there’s a rub: More pitch doesn’t allow the engine to rev up as high, so the top speed potential of adding pitch may be greater than the reality. Moreover, acceleration, and the ability to hold the boat up and at a steady speed at lower rpm (handy in many situations), is reduced. Think of more pitch as a higher gear: You can use it to start a vehicle moving or while climbing a hill, but it’s less than optimal. Compare the acceleration numbers of this “faster” prop with the other two Enertias and you can see the effect yourself.

Enertia props are smaller in diameter and have more moderate rake, and less aggressive cup, than the Mirage Plus props they superseded. But they have more blade area than fast bass-boat props.

Conclusions 1. A modern aluminum prop works fine, but a stainless-steel prop will outperform aluminum in every way. Only you can decide if that overall performance is worth $600.

2. In our test situation, the four-blade prop matched the performance of the three-blade stainless-steel prop, and it felt better from the helm. I’d spend the extra $80 for the Revolution 4.

3. It’s better to be underpropped than overpropped. A boat running too much prop pitch will feel doggy all over the operating range because the motor is always working a little harder. On the day you have a full load of passengers it will feel like a real slug. If you never run your boat near full throttle, there’s nothing wrong with running one size underpropped and enjoying better acceleration, not just on hole shot but also in the midrange, which is where you really run the boat.

4. If your boat already planes in four seconds, there’s not much room for improvement. If your boat planes in six to eight seconds, a better prop might make a difference you can really feel.

Our testing for this story only serves as an example. The tricky element of propping is that there are many variables that can affect how a particular prop works on a particular boat, including boat weight, weight distribution, engine/drive height, the hull form, the way water flows to the prop, the power curve of the engine, and on and on. The Mercury website, for example, has a prop-selector tool (mercurymarine.com/propellers/prop-selector/#) that will get you in the ballpark, but from there you’ve really got to demo each prop to see how it feels on your boat. Find a dealer that will let you test-drive a number of props before you buy. You can do your own testing with a GPS and a stopwatch, but also pay attention to how the boat feels with each prop. That’s an element of performance you’ll appreciate every time you run your boat.

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Choosing the Correct Boat Propeller

How Propellers Work

Design considerations, how to choose the correct pitch and blade count, choosing the right propeller by crowley marine.

The right prop will get the best performance out of your boat. Matching the propeller to your application, whether cruising, water skiing or performance, maximizes the power from your engine. It also helps with handling and acceleration. Use this guide to learn how different propeller designs affect efficiency, power, and speed and then learn how to choose the correct prop for your boat and application.

The propeller has a hub surrounded by blades of the same length and size. The blades are twisted so that they push water toward the rear as they turn. This pushing is what propels the boat forward in the water. Most blades rotate in a right hand (clockwise) direction when viewed from the rear. Left hand propellers are paired with a right hand propeller in dual-engine installations to keep the boat stable and reduce steering effort.

Pitch is the distance the propeller will move the boat after one revolution (not accounting for slip). A lower pitched propeller will create more power due to more engine RPMs, but the boat will move slower. A higher pitched prop allows the boat to move faster by travelling a farther distance with each rotation. When choosing a propeller, choose a pitch that will keep the engine RPM in its recommended operating range. Going under the range will cause the boat to lug, while going over can cause engine strain.

Blades have other important features built into their design. Rake is the angle between the blade and the hub. The rake angle can be flat, staying the same along the entire blade, or progressive, meaning the angle increases as it approaches the tip. Props have between 0 and 20 degrees rake. The rake angle determines how much the bow lifts out of the water. High rake propellers are ideal for light-weight, high speed boats. Too much rake, however, will strain the engine and reduce overall performance.

Some propellers are cupped, which means they have a lip on the edge of the blades. The cup creates more space between the sides of the blades, reducing ventilation and slippage. If the cup is on the tip of the blade, the blade has an increased rake angle and a higher bow lift. If the cup is on the trailing edge, it effectively increases the pitch size, and the propeller will create more power at the cost of engine speed.

Blades are also designed to prevent ventilation and cavitation. Ventilation is when air is drawn around the blades between the blade surface and the water. Ventilation increases RPM but reduces speed, especially during hard acceleration. The anti-ventilation plate mounted on the outboard helps to prevent this problem. Cavitation is caused by water flow disturbances around the blades. Disturbances cause water bubbles to boil and burst against the blades, which damages the surface and reduces performance.

The fewer number of blades a propeller has, the more efficient it is. However fewer blades will also increase the "vibration" you will feel. That’s why three blade propellers are the most common for general purpose boating. Three blades props provide the best combination of performance, speed, and efficiency. Some manufacturers also create four and five blade propellers to increase acceleration and reduce ventilation. A four blade propeller will improve handling and control for high-performance applications. Five blade propellers are good for rough water conditions and tow sports.

Finally, material is an important consideration for your propeller. Aluminum props are a great balance of cost, performance, and durability. Stainless steel is five times stronger than aluminum, dramatically improving performance and durability. Stainless steel propellers offer better acceleration and are less likely to be damaged from striking objects in the water. Stainless steel props will outlast aluminum multiple times over.

Left: a stainless steel propeller. Right: an aluminum propeller.

Before you dive into choosing a propeller, understand your boat’s intended use. Consider your average speed, load, and boating location. If you will be using the boat for multiple applications, you may need to switch props. The propeller choice directly affects the engine RPM and therefore its performance. Choose a propeller that puts the engine RPM at the midpoint or higher of the wide open throttle (WOT) range with a normal load. This operating range will translate to the highest horsepower available from your outboard. Refer to your engine operating manual for the operating range.

Once you know the operating range, consult the propeller guide for your engine to pick a combination of pitch, blade number, and material. Choose a range of propellers to perform a water test. Test the props under the same conditions that you would typically use the boat—same load, gear, and water. Set the trim angle so the boat has optimum speed on top of the water.

To test the prop, run the boat at WOT and observe the maximum engine RPM on a tachometer. If the RPM is below the recommended operating range, switch to a propeller with lower pitched blades. If the RPM is higher, switch to a propeller with higher pitched blades. Each inch of pitch size will change the RPM by 150-200 RPM. Aim for the midpoint or higher of the recommended operating range. Keep in mind that high altitudes will reduce engine power, so choose a lower pitch to achieve the same RPM as on sea level.

Engine height also affects the performance of the propeller. Once you find the right prop, adjust the engine mounting height to create the best balance between speed, maneuverability, and acceleration. Start with the anti-ventilation plate even with the bottom of the boat. Raise the engine one mounting hole at a time until performance is unacceptable, and then lower the engine one hole down.

Keep a spare prop onboard for emergency situations. One recommendation is to buy a spare propeller that is two inches lower in pitch than your standard propeller. This reduction in pitch is perfect for tow sports, such as water skiing, due to a slower acceleration and higher power.

Back- the low pressure side of the blade closest to the boat Cavitation- vaporized air caused by water flow disturbances Cup (blade)- the lip on the edge of the blade Diameter- width of the circle made by the tips of the blades Face (blade)- the high pressure side of the blade farthest from the boat Leading Edge (blade)- the blade edge closest to the boat Pitch- distance travelled by the propeller in one revolution Rake- angle between the blade and the hub Root (blade)- the edge of the blade attached to the hub RPM- revolutions per minute Slip- distance lost due to inefficiency Surface Area- the total surface of the blades Tip- the point separating the leading edge and trailing edge farthest from the hub Trailing Edge (blade)- the blade edge farthest from the boat Ventilation- air bubbles surrounding the blades WOT- wide open throttle

Propellers For Sale

Evinrude & Johnson

Yamaha Marine

Mercury Marine

Yachting Monthly

• Digital edition

Propeller antifouling tested: Prop Defender

• Theo Stocker
• July 7, 2021

How well does propeller antifouling work? Yachting Monthly editor Theo Stocker tests Prop Defender over a full season to find out

Preventing fouling on your prop can help cut down on fuel use

Protecting a propeller from fouling is not easy, thanks to high prop speeds, but infrequent use.

There are three possible approaches to take; polished metal, slippery silicone based coatings, or biocidal antifoul s.

By the end of the previous season, the generous fouling on the two-bladed fixed bronze propeller on our Sadler 29, Pasque , was costing us 1.5 knots under engine.

A season with Prop Defender yielded significant fouling from coral worm. Credit: Theo Stocker

Last season, it was time to try something else and we decided to put a new glass-reinforced, silicone-based and hydrophobic product to the test.

Prop Defender creates a slippery surface to which fouling will struggle to stick, and should slip off when it does.

It uses non-aggressive primers, making it suitable for all metals.

Although coral worm grew after a season with Prop Defender applied to the propeller, it was washed off easily with a pressure washer. Credit: Theo Stocker

It also contains no toxins, solvents, biocides or VOCs.

Application of the original product I tested is in three stages and proved to be pretty straightforward, though needs to be done carefully.

Start with a totally clean propeller before rubbing in the degreasing preparation paste with 180 glass paper pad.

Continues below…

Ultrasonic Antifouling Test

2009 Vs 2010 season photographs. 2009 Cruised English Channel, 1000 miles, Blakes Tiger Xtra 2010 Cruised from Gosport to Scotland…

Invasive species: How sailors can help tackle biofouling

While yachts are unlikely to introduce invasive species from abroad, they can help them spread around the coast. Sarah Brown…

How to antifoul your boat: a step by step guide

No one likes to antifoul their yacht, but keeping a boat free of the harmful growth is vital. Adam Fiander…

Next, scrub clean using the supplied detergent, and rinse off with fresh water.

Leave it to dry and don’t touch the metal with bare hands, as this can reintroduce grease.

I then applied the top coat with a brush – it needs 24 hours before it goes in the water and three days before use.

The company has since updated the product so it now has a two-stage hydrophobic top coat, which it claims makes the finish even more hard-wearing and slippery.

Verdict on Prop Defender

Our boat was in the water for a short six months this year and on the whole I was pleased with the performance of Prop Defender.

Our speed reduction from fouling was kept to a maximum of half a knot under engine, which is a good deal better than with bare metal.

During the main summer months, there was very little fouling to spot.

When we pulled the boat out of the water in late October, after a period of little use, there was very little weed or other growth, though more tenacious coral worm had been able to stick, and any other fouling had grown on this, rather than the metal.

Overall, it wasn’t a perfect solution, but a significant improvement on last season.

Specifications:

Price: £74.95 Coverage: 100ml or 2 applications for 24in prop Includes: Prep paste, detergent, top coast x 2, stirrers, glass paper, gloves, brushes Contact: www.prop-defender.com

Other propeller antifouling on the market

Hempel Ecopower Prop

A biocide-free spray, Ecopower Prop is used as a coating for propellers making it difficult for fouling to fully attach thus making it easy to dislodge and remove when cleaning.

It has a ‘self-renewing effect throughout the season’, and needs to be applied over a primer.

Price: From £22.99

Buy it now at Amazon (UK)

Buy in now at eBay (UK)

Buy it now at eBay (US)

Marlin Velox Plus Propeller Antifouling

A hard biocidal antifoul paint suitable for all metal types.

The active ingredient is zinc pyrithione, combined with soluble and insoluble resins to offer high adhesion.

It can be overcoated each season.

Price: From £43.95

Buy it now from Amazon (UK)

OceanMax Propspeed

Propspeed claims to be ‘the original propeller and running gear coating system’.

It’s a silicone based topcoat that creates an extremely slippery surface.

Manufacturer Oceanmax recommends that it is applied by a professional applicator.

Price: From £349.99

Buy it now from eBay (UK)

Buy it now from eBay (US)

Note: We may earn a commission when you buy through links on our site, at no extra cost to you. This doesn’t affect our editorial independence.

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Propspeed Test: Year 1

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Our editor Mark Corke applied a running gear antifoulant to his Grand Banks and came away impressed with the results.

Photo: Mark Corke

A fouled prop can cause a bunch of problems — from reduced top speed, increased fuel consumption, and unwanted vibration. When Seaglass , my Grand Banks 32, was out of the water just over a year ago for routine maintenance, it coincided with a chance to try out Propspeed , a special type of antifouling for propellers. I had seen it on other boats in the yard but had always been skeptical of the manufacturer's claims. Full disclosure: Propspeed offered, then provided, the product and application to me at no cost.

The proper application of Propspeed is critical to its performance and longevity, so I took photos while sales rep Keith Mayes showed me how it was done. Mayes explained that the key to a successful job is careful preparation. Any previous coatings and fouling must be removed and the prop abraded with 80-grit sandpaper before wiping down with solvent. Propspeed is available in a variety of quantities depending on the size and number of props that need to be coated. We used a 500-millileter (16.9 ounce) kit, which was sufficient to coat Seaglass's single 24-inch, four-bladed prop and small hydraulic stern thruster.

As with many projects, proper preparation is key. After thoroughly cleaning and abrading the props with sandpaper, a wipe-down with solvent is required before application. (Photo: Mark Corke)

Mayes carefully applied the coating using a foam roller and a chip brush for hard-to-reach areas. The yellow hue of the coating makes it easy to see any missed spots. Regardless, you need to work reasonably fast as there is a limited window of opportunity to apply the product before it starts to cure. This varies with temperature, so make sure you follow the instructions on the can.

A foam roller makes application quick on large props. (Photo: Mark Corke)

Propspeed made a video of one of their techs applying the product to a larger boat, but DIYers can pick up some helpful tips.

Propspeed 3 Top Tips For DIY

A couple of days later, the boat was relaunched and I was eager to see if the claims of improved speed and better fuel economy were true or just marketing hyperbole. I was more than impressed. I've run the boat enough over the years to be very familiar with its characteristics; at 1,800 rpm, the boat's speed is a consistent 8 knots. After application, running the engine at the same setting gave an increase in speed of a half-knot — impressive for a boat weighing close to 8 tons! Vibration was also noticeably decreased, but I suspect this was most likely due to cleaning off the barnacles and other marine growth before applying the coating.

Mayes told me that the coating typically lasts 12 to 18 months before reapplication is required. Because I haul my boat at the same time each year for maintenance, I was interested to see how the coating held up during the intervening year. When I pulled her out of the water for cleaning and application of bottom paint earlier this year, the prop was virtually completely clean of growth — very impressive.

So is Propspeed worth it? Overall, I think so. It is expensive at $400 for a product that only lasts a year, but there has been a noticeable increase in speed and fuel economy. By my estimates I'm using about a gallon less in fuel over an 80-mile run, and best of all no fouling of either the prop or stern thruster. I'm also a longtime sailor, so I'm acutely aware that any fouling on the prop has a profound effect on speed when under sail.

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Contributing Editor, BoatUS Magazine

A marine surveyor and holder of RYA Yachtmaster Ocean certification, BoatUS Magazine contributing editor Mark Corke is one of our DIY gurus, creating easy-to-follow how-to articles and videos. Mark has built five boats himself (both power and sail), has been an experienced editor at several top boating magazines (including former associate editor of BoatUS Magazine), worked for the BBC, written four DIY books, skippered two round-the-world yachts, and holds the Guinness World Record for the fastest there-and-back crossing of the English Channel — in a kayak! He and his wife have a Grand Banks 32.

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YAMAHA PROPELLER SELECTOR

WHAT YOU’LL NEED

Gather basic information about your boat, outboard(s), current propeller, and performance goals.

WHAT YOU’LL DO

You’ll enter this information in three successive steps using more refined input for each.

WHAT YOU’LL GET

At the conclusion of each step you will be presented with propeller recommendations based on your input.

FIND YOUR NEXT FLEXOFOLD FOLDING PROPELLER

Flexofold develops, manufactures,, and sells the most efficient folding, propellers for sailboats and, multihull yachts on the market..

Get a specified propeller recommendation for your sailboat

Our folding propellers are available as 2-bladed, 3-bladed, and 4-bladed in multiple sizes and pitches. All delivered for both shaft- and saildrive installation.

100 % FIT ON ALL COMMON SAILDRIVES

The Flexofold propellers fit perfectly on all common saildrives and are widely used by most of the recognised boatyards worldwide – including Beneteau, Jeanneau, Lagoon, Elan, Hanse Yacht, Dehler, Saffier Yacths, Halberg-Rassy and many more!

100% fit on all common shafts

The Flexofold propellers are designed to fit perfectly on all common shafts following the ISO; SAE and IMP standards, and are widely used by most of the recognized boat yards worldwide.

Worldwide delivery

Flexofold propellers  are delivered all over the world directly from our factory in Vejle, Denmark. No matter where you live or where your boat is located, we ship your new propeller by UPS courier service – directly to your address at very competitive costs. In most cases, we ship your new propeller within 3-5 working days from placing the order / receiving payment.

Our experience - your guarantee!

We pride ourselves in direct contact and dialogue with our customers, shipyards, and dedicated sailors from all around the world. This is why we can ensure that you get the right guidance and the best possible propeller for your sailboat!

Saildrive Propellers

Flexofold folding propellers for  Saildrive installation

Shaft Propellers

Flexofold folding propellers for mounting on Shaft

Spare Parts

Find  spare parts  for your propeller  here    

The best test for a propeller is the one carried out by the sailor himself!

Find the answers to the most frequently asked questions about folding propellers

Enjoy the performance and safety benefits that our foldable propellers provide

CUSTOMER REFERENCES

The Flexofold 3-Blade 17x13-3L/R propeller went on after the first attempt. The motors—2x Yanmar 3JH5—come to a nominal speed of 3000 RPM and the Outstar 48 goes at the speed of 9.5kn

Andreas Bock

The new outstar 48 with twin flexofold - germany.

Adding the 3 bladed Flexofold was the best thing ever. Should have done it years ago. Better performance under sail and power. Cut fuel consumption in half!

Mark Schneider

Smarter charter ltd. - usa, buy directly from the flexofold factory.

Get an offer for a Flexofold folding propeller.