A METHOD TO CALCULATE PROPULSIVE PERFORMANCE OF SHIP

This paper describes a theoretical calculation method for the propulsive performance of a ship. The ship hull in the double-body flow is represented by the source distribution on the hull surface, the propeller by the circulation distribution on the propeller plane, the rudder thickness by the source distribution and the rudder load by the vortex distribution on the rudder centre plane. The above singularity distributions are determined by each boundary condition. Using these singularities, the flow field and the forces such as thrust and torque, rudder drag are calculated. The wave flow around the hull, propeller and rudder is calculated using the Rankine Source method. Then the hull wave-making resistance and the wave flow can be obtained, including pressure distributions on the hull in the potential flow field. The author's then calculate, on the basis of potential flow field, the effective wake distribution just before the propeller plane. The wake calculation method is based on the thin boundary layer approximation and belongs to the integral method. This effective wake distribution becomes the input data of the propeller inflow in the potential flow calculation. By an iterative procedure, the self-propelled state of the ship is attained and the propulsive performance of the ship is obtained. Calculations for Wigley and SSPA720 hulls with a propeller and a rudder are performed, and the results compared with the experimental results. It was found that the effective wake and thrust deduction fractions obtained by the calculation agreed well with the experiments.