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Why not water jets?
By John Miele
Article Rating:
January 1, 2012 12:53 AM EST
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 446

Over the last few years, water jets have often been proposed as a viable alternative to using surface drives in fast vessels. Indeed, in certain applications, water jets can be a useful form of propulsion for small vessels. They are often cited for superior performance, especially in shallow water, such as harbours or near coastlines.

However, this situation is not always the case. Water jets have real limitations on performance that surface drives do not have:

  1. Susceptability to damage from marine litter, especially items that block intakes, such as plastic bags, means that water jets can be mechanically temperamental at times.
  2. Limitations on top speed (50 knots is normally the upper limit for water jets on most vessels. The top limit on surface drives is determined by hull strength, engine power, and the G-force that the human body can withstand.)
  3. Extra weight (From water)
  4. Much more expensive than surface drives, both initial cost and ongoing life-cycle costs.
  5. Less maneuverability than surface drives.
  6. Less thrust efficiency than surface drives.
  7. More cavitation due to air in the intakes.

There are, however, certain situations where water jets are preferable to surface drives:

  1. Situations when propellers endanger human life (As in dive boats)
  2. Water jets are quieter, with less vibration
  3. Better performance at slow, non-planning, speeds

At France Helices, we are focused solely on performance and meeting the customer’s requirements. When we make recommendations, in situations where a water jet makes more sense, we always advise the customer to purchase that equipment.

 

 

 

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Published January 1, 2012 – Reads 446
Copyright © 2012 SYS-CON Media, Inc. — All Rights Reserved.
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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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