Use of electromagnetic rim driven propulsor for waterjet propulsion systems

A concept investigation has been carried out into the possibility of using a tip driven electro-magnetic propulsor as part of a waterjet propulsion unit. The primary advantage is that there is no need to insert a drive shaft within the waterjet inflow. This significantly reduces cyclic variations in the propulsor inflow and removes an area of flow separation around the shaft. It also provides the designer with greater freedom as to the types of propulsion systems available and where they can be placed within the ship. The viability of the concept has been examined by considering the performance of an axial flow electromagnetic thruster developed for the ROV market and numerically studying its performance within a typical waterjet inflow. A study was also conducted to examine the scalability of such propulsion units. It is concluded that for a typical size of waterjet with an input power requirement of 110 kW and diameter of 0.25m the maximum delivered power at 2,200 rpm would be 90 kW. This design would have the benefits of no shaft induced losses and reduced cyclic blade loadings and should deliver a higher thrust than comparable conventional waterjet units using geared electric motor drives.