Oscillating foils for marine propulsion

The use of oscillating fins by aquatic animals for propulsion has inspired the design of corresponding propulsors for ships. Rigid and partly flexible oscillating propulsor designs were analysed for a large ship based on two-dimensional linear and nonlinear theories. Open water efficiencies of the oscillating propulsors were 17-25% higher than those of an optimal srew propeller. Behind the ship, quasi-propulsive efficiency of the partly chordwise flexible foil was 72%, i.e. 5% higher than that of the screw propeller. The efficiency increase produced by the oscillating propulsor was attributed to the considerable increase in the propeller working area due to the wide span of the foil.