THE EFFECTS OF INTERACTION FORCES BETWEEN SHIPS IN PROXIMITY ON THE DESIGN OF RUDDER SIZE AND RATE

Rational design of rudder size and rate requires consideration of operational demands on the control of the ship caused by the presence of another ship or restricted waters. A mathematical model is developed from a velocity potential description for each ship, consisting of a distribution of sources for the ship in open ocean and horizontal and vertical dipole distributions to account for the other ship in proximity and shallow water, respectively. The Lagally theorem is used to calculate the interaction forces and moments, and ship trajectories are calculated using standard ship equations of motion in the lateral plane. Linear control theory is used to control the rudder and speed of the ship to approximately simulate the action of the helmsman. Comparisons of theoretical forces and moments with model test results showed good agreement except for underprediction of these in shallow water. The effects of increases in rudder size and rudder rate on underway replenishment operations are simulated. The results show that changes in rudder control sensitivities have much greater effects than changes in rudder size or rate on replenishment operations. (Author)