New electric/hybrid waterjet propulsion system

One of the world’s leaders and pioneers in waterjet propulsion – Australia’s Doen WaterJets – has developed an electric/hybrid ready waterjet  to meet the increasing global demand it is seeing for clean marine mobility.

Started in 1971 by avid ‘boatie’ and mechanical engineer Fran Udvary, Doen was one of the first companies to focus exclusively on jets for recreational boats and quickly became known in the small boat and ski boat world.

From jets for ski boats to huge commercial vessels

Growing both in capacity and size of jets, the company expanded to supply dive boats in Japan, have their Doen DJ110 model specified by the US Navy for its 11m RIBs, work with MerCruiser to develop the MerCruiser Jet and now have a full range of waterjets used all over the world, the most powerful units driving boats as big as 90m / 300ft in length.

Because a waterjet is a propulsive mechanism rather than the thing that actually provides the power, the trick with any jet is matching it with the motor that does provide the power. Doen works closely with boat and engine manufacturers to put together the ideal motor/jet package for each vessel.

The new electric/hybrid ready model is designed to work with some of their Ultima Series smaller units and can accept the connection of a motor rated up to 150kW (continuous), about 200 horsepower.

Without getting overly technical, the major advance is their integrated Power-Take-In (P.T.I.) feature. This allows Doen to change input/output ratio for the best match for the electric motor’s power characteristics as well as the diesel motor’s specs in a hybrid configuration.

Simple system – no complex transmissions

It is part of a simplified system that means diesel and/or electric power can be converted to the waterjet as required without elaborate and expensive transmissions. It can also combine or disjoin the diesel and electric power at the waterjet for different modes of operations: Diesel Only, Electric Only, Diesel + Electric and Regeneration, as seen in the diagram above. This is similar to the switchable hybrid motors and systems used in the City of London’s new pilotboats, but with a waterjet providing the propulsion instead of a propeller.

The diagram below shows how the waterjet can be used with a pure electric motor. In both diagrams the Doen PTI interface is shown in red.

The other advantage is that the waterjet is integrated with Doen’s electronic control platform so the power from the motor/waterjet is managed seamlessly.  From the Captain’s point of view, the propulsion and ships control at the wheelhouse remains unchanged; regardless of the specific mode of operation.