The new CEM JET propulsion unit is ideal for internal combustion engines and powerful brushless motors, as thrust reversal is obtained by operating the reversing flap rather than by reversing the direction of rotation of the engine. The steering nozzle incorporates an integral cooling water nipple. Suitable power plants are internal combustion engines of 15 to 30 cc capacity, and electric motors rated at a minimum of 700 Watts output power.
The Jet drive is usually epoxied into the hull, with a rectangular hole cut 65mm wide by 155mm long right up to the transom bulkhead, a circular hole approx. 55m diameter is cut into the bulkhead, and the nozzle from the back of the drive goes through that. The main control, exit nozzle is then mounted over that and screws through the bulkhead to attach to the main jet unit.
Length approx. 285mm.Width approx. 78mm,
Height approx. 85mm, Impeller 49mm
The Jet propulsion unit, also known as a water-jet unit, is primarily fitted to exclusive high-speed motor yachts, ferries, racing boots and similar full-size vessels. In principle this power system consists of a pump which sucks in water though an opening in the bottom of the hull, accelerates it by means of an impeller, then forces it out again through an opening in the stern. Newton’s law of motion now applies: the jet of water expelled at the rear generates an equal and opposite reaction in the boat’s hull.
Boats with Jet propulsion units can operate in very shallow waters, as all the parts usually mounted below the hull, such as propeller, shaft, shaft bracket and rudder, are eliminated. Initial acceleration with a jet unit is very high, and this can be a distinct advantage in certain types of boat such as dragsters. The heeling moment produced by conventional boat propellers is completely absent. Since the water in a Jet propulsion system has to cover long distances in narrow ducts, there are inevitable friction losses which require rather more energy than for an orthodox power system.
