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Propeller efficiency by type

When it comes to designing propulsion systems for fast craft, the type of propeller becomes important: Different types of propulsion have different levels of efficiency associated with them.

Surface drives use supercavitating surface piercing propellers, that are more efficient at very high speeds. Indeed, on vessels that will operate primarily below 35 knots, a surface drive is not a good choice of propulsion, since surface piercing propellers are less efficient at low speeds. Indeed, for slower vessels, water jets might be a better choice. The chart below lists several types of propeller: (Allison, J. (1978). Propellers for high-performance craft)

Looking at the graph, it is immediately apparent that water jets are far less efficient at higher speeds, and the efficiency of fully submerged propellers drops precipitously at speeds over 55 knots.

This is why surface drives are the only technology that has the capability to deliver performance at high speeds.

One other consideration that impacts efficiency is that of propeller slip… The loss of efficiency (thus, speed) as a result of drag. This, in particular, is one are in which surface drives excel. Since drag is minimized, very little slip is experienced. Typically, slip % on sirface piercing propellers averages 7% – 12%.

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More Stories By John Miele

I am currently Sales and Marketing Manager, Asia / Pacific for France Helices. Created in 1977 by Paul BEZZI, FRANCE HELICES is today an international company. French marine propulsion leader, FRANCE HELICES is also one of the international leaders. Research and development are a very important part of FRANCE HELICES program, the CAD's department is equipped with the latest computer technology, using most up to date programs. Our engineers and technicians determine from the customers specifications and designs, the type of propulsion system to suit the boat's application. They can also advise on the ideal choice of power and optimum gearbox ratio to obtain the maximum thrust. There are many FRANCE HELICES' inovations and patents such as Surface Drive System (SDS) which enable boats to obtain very high speed with excellent handling capabilities and high quality Controllable Pitch Propeller systems (CPP) for both professional use and pleasure application. The constant research using cavitation tunnel testing, guarantees high efficient propeller blade shape for our customers. More than 20 000 propellers per year are manufactured by FRANCE HELICES workshops. In all sizes from small sailing boats to large fishing vessels to navy boats or mega yachts. The FRANCE HELICES workshops are equipped with modern foundries capable of casting propellers up to 3.5 tons in NiBrAl. They are also equipped with CNC milling machines and CNC lathe machines. FRANCE HELICES has four sites which cover the complete range of production. The development of FRANCE HELICES, supported by shareholders places our company as a leader in the international market and insures a constant development, worldwide, in order to be close to the end user.

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