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What is a cavitation tunnel, and why do we use it?

cavitation tunnel

France Helices actively promotes the fact that all of our products are “tunnel tested”. We are proud of the fact that we take the time and spend the money to ensure our customers that what they buy from us is actually what they receive. France Helices is the only propeller maker in the world that can make this claim and back it up with hard data.

Why do we do this?

Quite simply, the only way to truly measure the efficiency of a propeller, either surface piercing or conventional, is to actually test the propeller using the scientific method. A cavitation tunnel allows a manufacturer to design a propeller, model it, and actually test the impact of the propeller on the hydrodynamics of the vessel. A cavitation tunnel is much the same as a wind tunnel: water flows through a chamber and strobe lights allow us the ability to “see” the water flow around the propeller. Since cavitation is basically air bubbles, the efficiency of a propeller, or the impact of cavitation on a particular design, is immediately apparent.

Why doesn’t every propeller or drive manufacturer tunnel test?

The answer is simple, and three-fold:

  1. It is very expensive. A design is first created, and then a model needs to be molded and cast. Then, based on data, the process is repeated, with different models tested until a design meets specifications. This process can become very expensive, very quickly. Every test we conduct costs in the tens of thousands of Euros. Additionally, for surface piercing propellers, most tunnels are not technically able to test, so modifications to the tunnel, itself, must be made. Though those changes are a proprietary company secret, we can advise that the cost is in the hundreds of thousands of Euros paid by France Helices.
  2. Cavitation tunnels are often created by the military and based at universities for research or defence purposes. Most tunnel locations have very strict approval processes or may be limited to “national” companies or personnel. The tunnel France Helices uses is restricted to French nationals and French companies.
  3. There are relatively few such facilities worldwide, and even fewer are of adequate scale to fully test. The infrastructure cost of building a tunnel is enormous, and few governments are willing to spend the amount of cash necessary to build a proper facility. France Helices uses the tunnel in Val de Reuil, France (LINK). Therefore, because of the scarcity of facilities, cavitation tunnels are often fully booked months, or even years, ahead of time.

By using a tunnel to test our designs, France Helices guarantees propeller thrust 100% on every propeller we make. Not only are we the only propeller maker in the world whose products are fully classified, we are the only manufacturer whose products can be classified. Why? We have the data to back up all claims we make. We know, 100%, the impact of cavitation on that propeller. We know, with 100% accuracy, the actual Kt and Kq curves of ever propeller we sell. No factors. No guesswork involved. Our calculation software for surface drives gives accuracy beyond any other drive manufacturer. That is one reason why we are often asked to quote propellers for drives made by other manufacturers, like Arneson. The buyers know that no other propeller manufacturer in the world can give such accuracy.

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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.