Folding Propellers vs Feathering Propellers
It is well documented that a fixed propeller is a bit like towing a bucket and can create a considerable amount of drag when sailing. Dragging a three-blade fixed prop through the water under sail could reduce your boats speed by up to a knot of boat speed – adding up to an hour to a 20-mile day sail!
There are three clear solutions to reducing propeller drag.
- Folding propeller – where the blades quite literally fold closed
- Feathering propeller – where the blades turn parallel to the flow of the water, and;
- Self-Pitching propellers – where the blades seek their own pitch determined by shaft rpm
Swapping to a drag-reducing propeller is a significant investment, but also one that will keep paying back. Your boat should point slightly higher and also give you more performance under sail, making sailing more enjoyable!
A folding propeller like a 2B Flexofold is usually the simplest and cheapest way to minimise drag when sailing – and test after test has shown this to be the case. In benign conditions a Flexofold 2B propeller is very efficient!
Folding propellers can have up to four blades that close in on themselves from as little as one-knot under sail. Depending on the blade shape and pitch, folding props typically provide very good thrust moving forward similar to that of a good fixed propeller. However, because the propeller relies on centrifugal force to hold it open in reverse, higher revs are needed to drive against the thrust that is trying to close them. Sometimes this can cause a problem if a hull already suffers with prop walk.
Folding props are best suited to faster, lighter fin keeled easily driven hull forms that handle well under power and where reversing is less critical.
Feathering propellers such as a FeatherStream can be found with 2, 3, 4 and 5 blade models all of which are matched to the boat and engine installation. A feathering propeller will produce good forward thrust similar to that of a fixed prop and typically be on par with the performance of a folding propeller when under sail.
The blades of a feathering propeller are designed to align themselves with the water flow and because they need to present a neutral cutting edge to the water, the blade profile is almost flat.
This means that the prop is slightly less efficient than a curved blade when driving ahead, but because the pitch completely reverses when the engine is going astern, this gives enhanced stopping ability and more powerful astern thrust. This efficient angle of attached means less rpm in reverse thus less prop walk.
On virtually all feathering propellers it is possible to adjust the pitch, meaning you can fine tune engine loadings to suit your requirements.
Propeller Pros and Cons
|Lowest drag under sail||Weaker reverse thrust|
|Simple design||Can wear faster|
|Lower maintenance||Can increase prop walk|
|Excellent forward thrust|
|2B offers cheapest option|
|Superior maneuverability under power||Usually more expensive|
|Better reverse thrust||Requires annual maintenance|
|5% less efficient|
|Reduced prop walk|
|Automatically feathers to give minimum drag|
|No need for a shaft brake|
|Fits into restricted apertures|
|Average sailing speed is often increased by 15%|
If you spend more time sailing than motoring, or you enjoy the odd race, fitting a folding or a feathering prop is a worthwhile investment. Our own FeatherStream propeller has demonstrated that sailing hull speeds can be increased by as much as 15% compared to fixed 3 bladed propeller.
Combine that with the additional control you get at close-quarters under power and you have a winning combination.
Whichever prop you decide to fit you will see improved performance on a standard fixed-bladed propeller when sailing.
If you need any assistance do not hesitate to contact us where one of our engineers will be happy to discuss your requirements.