Radar observations of encountered wave profile and measurements of vessel motions have been used to derive motion response amplitude operators, and the results are compared with predicted motion responses. Data were collected from an INCAT Tasmania built ferry while on delivery between Australia and England. It has been found that the predicted motions using a time domain method are consistent with those observed with respect to the increase of response with vessel speed and the decrease of response for seas encountered from the beam directions. Peak heave and pitch response amplitude operators were measured and computed at up to 2.5 and 1.8, respectively, at high speed in head seas. Conventional low-speed frequency domain motion analysis was found to give smaller predicted responses at somewhat higher frequency than the high-speed time-domain motion analysis. Significantly larger rolling motions were measured than predicted, and it appears that the action of the steering system may contribute substantially to in-service rolling.

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