CONTRAPEL
A NEW TWIST TO PROPULSION
BY KEITH INGRAM
I
t was back in the 1990s when brothers Barry and Richard
Davies were working on the counter-rotating impeller principle
in their garage as a means of raised protected propulsion.
Water-jets have an impeller or multiple impellers that rotate
in the same direction. They also have water-straightening vanes
called stators and a nozzle for accelerating the water, which is the
source of the thrust. Essentially they are a very large water pump
thrusting through a steerable nozzle.
The Davies made several counter-rotating statorless prototypes,
however they were disappointed to discover that the expected
efficiency and performance gains were not forthcoming, clearly
old Bill Hamilton had been down this path before.
The project stalled until, "eureka" the moment when it was
postulated that perhaps the nozzle and associated pressure-head
was the source of the loss and that reversing the thrust formulae
to replicate propellers may be a better way to approach the
problem. This possible solution was not obvious; as it is counterintuitive that slippage within an enclosed system would generate
higher propulsive efficiencies, particularly at low boat speeds.
To test this theory, a completely new way of looking at the
device was required. They proposed that instead of accelerating
the water in a nozzle section, it would be possible to accelerate
the mass earlier from out of the intake pick-up duct and then
simply "dump" the water through the outlet. A water-jet intake
pick-up duct is located upstream from the impeller and delivers
water above the waterline when the craft is planing.
This was a complete departure from existing thinking as
20 Professional Skipper May/June 2013
counter-rotating blades could now essentially be configured
as water accelerating propellers and not pressure inducing
impellers. "Aligning the theory more closely with the high mass
flow, low plume velocity parameters of efficiency, as defined
by the scientist Froude, was looking to be a good option," said
Barry Davies.
The Davies brothers' initial test results were reportedly
exceptional, so they proceeded to form a company called
ContraJet Ltd and patent the concept. However there was an
unexpected fly in the ointment, a mysterious manufacturing
fault was causing Barry great concern. He felt that the basic
understanding of the hydrodynamics may have been flawed,
leading to doubt over the efficacy of the ContraJet patents.
Unable to solve the problem and produce a viable product,
ContraJet Ltd was forced to shut its plant in 2000.
Barry and brother-in-law Paul Paterson believed that new
research could provide the elusive answer. Following the
formation of a company in 2002 called PropellerJet Ltd, a series of
amazing discoveries were made, which led to a completely novel
understanding of the hydrodynamics and drafting of new patents.
The hydrodynamics were extremely complex and it wouldn't be
until the system was fully understood that construction of several
extremely efficient and versatile prototype water-propulsors
were built and new patents could be drafted. These advanced
devices would be capable of carrying out the functions of both
propellers and water-jets. Furthermore, Paul and Barry also
discovered a radical new field of hydrodynamics and named it
