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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.

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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.

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Q-Marine announces Next Generation Q-SPD Drive Systems

Published on February 21, 2019

This is a complete redesign of the original Q-SPD Systems incorporating the same successful construct as the original SD series plus many refinements in function, form and performance. Q-SPD Surface Drives are the most effective surface drive option on the market, negating the issues that come with trimmable surface drives, the simplicity of the fixed drive has so many advantages: Not having to worry about getting the trim right, over loading the engine, or having hydraulics and more components where the chances of something going wrong are greater.

The result of this redesign is a fully integrated propulsion solution designed for maximum longevity, that requires the least possible maintenance. Q-SPD’s construction is largely composite, the main housings is moulded from e-glass and carbon-fibre then reinforced in an epoxy matrix, using resin infusion manufacturing techniques, so they are exceptionally lightweight. More than 50% lighter than other brands giving benefits and offer the ability to create more complex and versatile solutions for the customer. The integrated system also now offers a premium Steering package by Hypro Marine on all systems and have custom exhausts options available.

Q-SPD Surface Drives are transom mounted letting you utilise valuable aft real-estate while all housing of vital mechanics and components are inboard away from the harsh marine environment, giving easy accessibility for the minimal routine maintenance and service needs.
Installation is easy with a bolt-in system – length of solution installed is shorter then any other, allowing more waterline, and in-turn more buoyancy. Twin rudder design is standard for more effective and responsive manoeuvrability and propeller protection.

“We are finding that Q-SPD is what the commercial and work boat vessels are choosing to use purely for the reliably and longevity of the Q-SPD System. Q-SPD has proven to endure thousands of hours without significant servicing requirements giving the end user added benefits.” says Leigh Michau, Managing Director Q-Marine International Ltd.

Manufactured using latest technologies in composites and marine friendly materials means they are very light weight and strong, giving a wide range of power for recreational and commercial applications.
The QSD New Generation Series is suited to vessels typically from 8 meters with power options from 180hp to 3600hp, or vessels up to 100 tonnes or more for more information visit www.q-spd.com or email Leigh Michau leigh@q-spd.com

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