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Based on the linear water wave theory, numerical simulations are carried out for motions in waves of a body moored by a nonlinear-type mooring system. Numerical results obtained by using the equation of motion described in the time domain with a convolution integral (C.I. method) are compared with those of the second-order linear differential equation with constant coefficients (C. C. method). These results are also compared with experimental values measured from the initial stage when the action of exciting forces starts and the validity of C.I. method is discussed.

SummaryThis paper describes a new anti-broaching steering system. This system aims to prevent broaching, which is the major mode of capsizing or large roll angle for a relatively high-speed ship in following and quartering seas. It is a kind of auto pilot system that realises extremely large rudder angle for small deviation from the desired course. Experiment was carried out in a seakeeping and manoeuvring basin for a self-propelled model equipped with the anti-broaching steering system. While the model suffered typical broaching in quartering waves with a conventional auto pilot, the model with this steering system successfully avoided broaching under the same operational and environmental conditions.

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