Self-propulsion test

A self-propulsion test runs the ship model with its own working propeller in the towing tank, so resistance and propulsion are measured together at the correct loading. Because the model friction is proportionally higher than the ship’s, a calculated tow force (the skin-friction correction or load-to-thrust deduction) is applied to set the propeller to the ship self-propulsion point. From the measured thrust, torque, and rpm the procedure extracts the wake fraction w, thrust deduction t, and relative rotative efficiency, which combine with the open-water propeller curves into the quasi-propulsive coefficient. It is the propulsion half of the ITTC-1978 method, the resistance test being the other half.