Thrust Deduction Prediction For High Speed Combatant Ship

The free surface effects on the hull-propeller interaction characteristic of thrust deduction have been studied for a high speed combatant ship hull form. Through mathematical modelling and a series of numerical computations, we attempt to elucidate the mechanism of this component of hull- propellent interaction from the free surface. SWIFT, a linearized free surface potential flow solver using a higher-order panel method, has been extended to study the interaction between the double hull and propeller as well as the hull-propeller interaction under free surface waves. The propeller is simulated using an actuator disk. Thrust loading coefficients from propeller open-water tests provide the sink strength for the disk. This ship has inclined propeller shafts and the measured wakes at the propeller plane clearly indicate that the propellers; are operating outside the turbulent boundary layer at the ship stern. The viscous effects are not treated here. The pressure on the hull is integrated to obtain the resistance for the double body flow with/without propellers, and also for the body and free surface flow with/without propellers. The computer thrust detection fractions show good agreement with the experimental data. For this particular ship, the free surface wave effect on thrust deduction is not small and lies between 25% and 30% of the total, depending upon speeds.