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Types of Sail Boat Propellers

There are four types of propeller currently available on the market for sailing boats. Gone are the days when the choice was at most between a “three fixed blades” and a “folder”. Now there are several alternatives available on the market supported by well-established companies, and they are all of interest to the cruising sailor.

Fixed Propeller

This is generally a mass production propeller par excellence, the one supplied with new production yachts mostly because of the price. This is indeed the cheapest and will provide good thrust. On the other hand fixed blades also mean greater resistance in the water when sailing so are not the most desirable option for sailing yachts.

Folding propeller

Available in two, three and now four blade. The blades close together and offer minimum possible resistance under sail. These originated primarily for the racing skipper to improve regatta performances. Some of the older designs were a significant compromise in terms of thrust and when backing down but mostly they where a means of auxiliary propulsion. Modern designs have improved dramatically, although astern performance is still a little limited, as the blades need to open against the water flow when going astern. Some of the very latest designs incorporate small blade overlaps, the rotation of the shaft uses the water pressure as well as the centrifugal force to help open the blades, especially when backing down. Three blade versions are often seen as a less expensive alternative to the feathering options. They are as good as a fixed prop under power in most cases but lack “bite” when manoeuvring. The four blade version is better for low noise and smooth operation. On larger yachts with high-powered engines there is a tendency for propeller cavitation. Particular over 100hp where cavitation manifests itself as noise and vibration, an uncomfortable idiosyncrasy in the aft cabin or owners stateroom on a luxury yacht. It is important to calculate blade loading before specifying a propeller for a heavy displacement yacht with a powerful engine.

Two, three and four blade feathering propellers (adjustable pitch propellers):

The blades, in the “sailing” position self-adjust by positioning themselves like a flag relative to the flow of water, ensuring minimum resistance. The blades have a flat shape, without helical pitch distribution or skew and can be a compromise under power but this is said to be the off set by their low-drag. They have manual adjustable pitch and the blades present the leading edge in ahead as well as astern. The pitch adjustment can help improve performance at the cruising rpm but this setting will reduce the maximum allowable engine rpm and thus overload the engine. Modern compact diesel engine manufacturers like the engines to reach the maximum rated engine rpm under load. The feathering propeller is a very good low-drag alternative for a long keel vessel with a small propeller aperture.

Controllable Variable Pitch Propeller

Automatically Variable Pitching Propeller

Available in two and three blades. This is known as the Autoprop, a unique design, which offers better performance motoring and motorsailing. The blades adjust their pitch angle automatically by sensing the forces and load characteristics acting upon them. The balancing of these opposing forces, centrifugal and hydrodynamic, produces the optimum blade angle of attack for any given engine rpm. You therefore need less rpm and consequently use less fuel thoughout the engine’s motoring range. This makes it ideal for cruising speeds under power and will be faster at any given rpm than a fixed pitch propeller. This also helps when motorsailing as the blades pitch up with the contributing aid of the sails – whereas a fixed propeller needs to be over-revved to catch up with the driving force of the sails. Like a feathering propeller the blades also lead in astern as in ahead and prop-walk is virtually eliminated due to the fine pitch setting at low speed manoeuvring. Overall this propeller is the least compromise over all the other folding and feathering types and will actually improve your motoring performance over a fixed pitch propeller. Difference in drag over other folding and feathering propellers is marginally more and probably not the answer for the racing skipper. You can still expect to gain ½ to ¾ knot under sail with the Autoprop.

Specifying a propeller for your yacht

While the designs of boats and equipment have changed over the years, the propeller configuration remains essentially unchanged. Pitch, diameter, shaft taper details and clearance available are the basic requirements when specifying a propeller. Pitch and diameter are calculated using the maximum engine horsepower, engine rpm and gearbox reductions ratio. The waterline length, beam and displacement are also used to calculate the correct propeller model including the hub and blade configuration. The engineer requires all these details in order to offer you the optimum propeller diameter for your boat.

Folding and feathering propeller types suffer from cavitation compared to fixed propellers because of their functionality and narrow long blades. Depending on the type of installation, excessive blade loading can induce higher noise levels and vibration will be more prevalent. The blades need to fold or swing past each other when going into astern and therefore cannot overlap. The blades are also thick and flat compared to fixed pitch propeller designs, this further reduces the propellers’ efficiency. All told, the design scope is much broader with a conventional fixed pitch propeller. For example, you can modify blade area, pitch distribution, skew, blade rake, diameter and so forth, all of this helps make the propeller work better, given all the design parameters. Unfortunately these elements are not as flexible with sailboat propellers and therefore users sometimes have to accept a compromise when fitting a feathering or folding propeller.

For the very best motoring and sailing performance, one should determine the space available for the largest diameter propeller, allowing for the recommended blade tip clearance. A large slow turning propeller is more efficient over a smaller faster turning one, particularly for a displacement yacht. Unfortunately, sometimes you may not have an engine and gearbox combination to match a propeller of this type and therefore your performance under power would be compromised. To obtain the best solution for any given engine, gearbox combination and yacht you should consult a propeller expert who will carefully consider all the essential elements to a good installation. Don’t be forced to buy a particular brand because it may not be the best solution for your application.

Making the correct choice and comparing the many propeller brands available can sometimes be confusing. Many of the feathering and folding propellers appear quite similar in design and superficially offer similar performance too. The Autoprop is the exception to this, with clear advantages motoring and motorsailing. Try to find independent advice or talk to an existing user of the prop you wish to buy, because the propellers’ performance can very subjective. You need to know the basics and establish your performance criteria in order to find the right propeller for your boat.

Welcome to our new website!

We are pleased to announce the arrival of our new website and new look for Q-Marine International Ltd.

It is only fitting that, for our first news article on our new site that we announce a new website for our business.   The ecomonic downturn has had some impact on all local and global companies one way or other, and we are no exception.  It has been a very quiet couple of years, industry wide, yet with a lot of changes, developments and advancements in all facets of the industry.  We have been kept alive by pure hard work and dedication plus some sacrifice, but mostly becasue of our loyal customers, whom we thank for your ongoing support.  We intend to keep up the effort and further enhance our products and services, to regrow our own business and to continue to offer our clients, old and new, some of the most innovative marine propulsion products on the market today.

We have some exciting advancements in the pipeline for the year ahead which will be announced as they evolve.  Meanwhile we continue to offer world leading products such as Bruntons Autoprop and Varifold yacht propellers,  Python Drive antivibration products, our own Q-SPD propulsion system and our retractable shaft drive for racing yachts.  We will also increase our involvment in supply of conventional dirve line components such as propeller shafts and shaft seals along with custom deigned and built components for the more special appications.

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In the meantime, have a quick browse through our new website, and feel free to contact us at any time!