Limits to Control of Ship Capsize Using Cycloidal Propellers Compared to Active Fins

A non-linear mathematical model, for the roll-yaw behaviour of a ship, is used to predict the prevention of capsize of a small ship. The problem was simulated using the digital package SIMULINK. Simulated responses of the ship with simple hydrodynamic fin stabilisers show that capsize could have been prevented by this means in waves up to 7 m in height. Active control using a simple full span control flap is used to show a reduction in roll angle to much greater waves. These results are compared to the use of cycloidal propeller propulsion to provide lateral thrust and hence roll control, which showed that this method can also reduce the roll. In order for successful roll reduction with a cycloidal propeller the response time constant is determined. In this example the roll reduction is greater in the fin example but this ability falls off rapidly with forward speed. Roll control using the cycloidal propeller has the advantage of retaining its’ effectiveness at low or zero speeds. To be fully effective for this ship, the reaction time to generate the side thrust from the roll actuation signal must be less than 13 seconds for the cycloidal propeller to prevent capsize. This would imply the use of the cycloidal propeller for roll control is better suited to larger ships.