Frequency domain analysis in seakeeping: a fast Ro-ro ferry case study

Frequency domain computations are commonly used at the design stage to investigate in a fast and practical way the behaviour and performance of ships. They are also used to select the most relevant conditions for the model tests. The increasing service speed at sea and the new trends in the lines of high speed Ro-Ro vessels yield new areas of investigation and challenges for naval architects. Among the factors which must be carefully considered in the seakeeping of such vessels are the risk of green water at the bow, potentially high acceleration levels, course keeping and roll motions in stern quartering waves and stabiliser fin efficiency. The added resistance in waves should also be determined as early as possible in the project in order to give the designer and ship owner a better estimate of the required service margin. This paper indicates the possibilities of frequency domain computations, their reliability and accuracy and possible areas for short-term improvement. The discussion will be based on a recent investigation through model testing on the performance of a high speed Ro-Ro ferry designed by FINCANTIERI. These test results are compared with calculations based on (2D) strip theory and 3D diffraction theory, performed jointly by MARIN, CETENA and FINCANTIERI.