A controllable transom flap in planing boats not only may reduce the resistance at cruising speeds in still water, but also could be designed to make a boat run at or near optimum attitude in various environments, which results in a reduction in both resistance and vertical motion in waves.
In the present study, considering the controllable flap as an exciting force and moment, the motion equations of high speed planing boats with controllable flaps in regular waves have been based on a modified strip theory. An attempt is made to evaluate the feasibility and effectiveness of the controllable flap as a means of controlling the running trim to optimize the overall performance.
The theoretical calculation pointed out that when the force and moment excited by flaps were in phase with wave disturbances considerable vertical motions would be set up, but once a suitable phase could be established between flap exciting forces and wave disturbances, the controlled flaps would reduce the motion amplitudes effectively.
Model tests carried out in the Ship Hydromechanics Laboratory of the Delft University of Technology have also shown that controllable flaps may be used not only for minimizing resistances in various conditions, but also for reducing heave and pitch motions, especially at or near the resonant frequency. The tests also proved that in automatic systems of controlling flaps, a pitch velocity feedback to the flap is effective.
