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How to Measure Pitch

We just linked to an interesting little blog, Naval Architect and His Profession. One of the postings on there was a basic “How to Measure Pitch” article that gives a very simple overview of pitch and how to visualize pitch.

A propeller can be defined as follows: A mechanical device formed by two or more blades that spin around a shaft and produces a propelling force in ships/boats.

There are various technical terms to define the propeller’s characteristics such as: diameter, pitch, disc area relation, hub, bore etc. All these characteristics are calculated to design the optimal propeller accordingly to specific needs of the ship owner and ship characteristics.

In this blog entry, we are going to define what is the propeller pitch and the importance at the time to select it.

Pitch: Is the displacement a propeller makes in a complete spin of 360° degrees. This means that if we have a propeller of 150” pitch it will advance 150 inches for every complete spin as long as this is made in a solid surface; in a liquid enviroment, the propeller will obviously slide with less displacement.
The pitch concept is not exclusive for propellers, other mechanical devices like screws also use it. For instance, a screw with 5 mm of pitch will advance 5 mm for every complete turn when hit by the screwdriver. In fact, the “screw propeller” concept is literally making reference to that the propeller works exactly like a screw.

It is very important that both, pitch and diameter, are properly calculated. If for any given HP the pitch is too big, the propeller becomes heavy and demands more power than the engine can reach and vice-versa, if the pitch is too small then we have a light propeller that wouldn’t absorb the engine’s full power.

So, what would be the appropriate pitch? Certain parameters need to be checked like power, rpms, gear reduction, size of vessel, vessel application (i.e. a trawler or a tugboat needs power while a yacht requires velocity).

I encourage you to read the article… It is an excellent primer.


Read the original blog entry...

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.