Propellor Not Impeller Key in New Boat Propulsion System

By George Backwell at November 10, 2012 05:52
Filed Under: Company News, Research & Development

A unique new propulsion system for boats was shown off for the first time at the recent Auckland On Water Boat Show. The Contrapel Hybrid Drive, the fruit of some eight years R&D, is claimed to be so advanced that it carries out all the functions of both propellors and water jets with none of the drawbacks of either. Notably it can continue operating in brown and black waters.

Founder of the New Zealand company, Barry Davies, explains the technology succinctly: “ The Contrapel technology is a propeller system working above the waterline. Externally it resembles a traditional water-jet, however, internally the method for developing thrust has much more in common with conventional propeller systems.”


Contrapel Propulsion System Units: Photo credit Contrapel

Key to the system is a pair of contra-rotating, fully enclosed hybrid propellors (‘hybrid’ in the sense that they are composed of different things) that operate above the water line.  Their purpose is to accelerate the water from out of the intake (pick-up) duct and then discharge it through the outlet, requiring only enough back-pressure downstream from the propellers to keep the system primed.  The conventional water-jet on the other hand does not accelerate the water until further downstream in the nozzle section, which makes it vulnerable to blocked water intakes.

These Contrapel hybrid propellers produce lift in a similar way to open water propellers, by using slippage, enabling the mass component for each revolution to be maximised and the plume velocity to be minimised in contrast to the low mass per impeller revolution and high-plume velocities present in conventional high-speed water-jet designs.
The manufacturer has tested the system in 190mm, 270mm and 330mm diameter configurations, and says it is suitable for a wide range of propulsion applications in crafts both small and large, demonstrating the following advantages over conventional water-jet systems:

  • Operable in extreme conditions, including brown and black-water environments.
  • Vastly improved thrust at low and mid speeds
  • Better fuel economy at low and mid speeds due to improved control.
  • Significantly lowers noise and vibration levels


One of New Zealand’s leading boatbuilders, Stabicraft Marine was involved in the development of the new propulsion system and fitted two Contrapel 330 mm units to its aluminium alloy hulled 10.2m Supercab rescue vessel. 

Powered by twin Volvo-Penta D6 435hp engines, this fast and handy vessel displaces about 8 tonnes with four persons on board plus 750 litres of fuel. With the Contrapel propulsion system cruising speed was 29.7 knots @ 3030rpm and maximum speed 37 knots @ 3500rpm.


Supercab Rescue Boat: Photo credit Stabicraft Marine

Comments (2) -

Would like to see some video please beside some more tachnical data regarding compatibility with different hull models and design and speed effective factors.
Regards
Lt. Col. Eng. Ali AlShakhs
Kuwait

ALI ALSHAKHS |     11/15/2012 4:27:37 AM #

If one googles www.contrapel.com you can review various videos showing different sizes of unit in various boats being tested.

Regards

Barry Davies (inventor)

Barry Davies |     11/18/2012 11:15:51 PM #

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