RESEARCH ON SHIP CONTROLLABILITY PART 4. NON-LINEAR PREDICTION OF STEERING PERFORMANCE OF SERIES 60 MODELS

Hydrodynamic forces and moments due to ship motions in the horizontal plane were obtained at the rotating-arm facility of Davidson Laboratory, in tests of 5-ft Series 60 models. Results were used in computations of ship motions in calm water. A digital computer was used to make non-linear predictions of ship response to rudder action and these predictions are compared, in the report, with trajectories of a free-running model. They are found to correlate satisfactorily. On the basis of this correlation and by means of the same computation, variations of ship maneuvering motions with changes in ship configuration are examined. The ship configuration parameters which are varied include rudder size, block coefficient, draft, breadth, profile, and section shape. The relationship between maneuvering response and rudder rate is examined, using non-linear computation, to obtain a basis for determining optimum rudder rate for ships of different speed and size. Computed results show that the minimum rudder rate presently allowed by the rules and regulations is adequate for ocean trading ships of ordinary size and speed; however, this adequate rudder rate could be lower for very large, relatively slow ships, such as supertankers. ( Author )