This paper looks at developing a numerical model of a ship and its tow system as the tow system is winched in during high sea states. The focus is on the vertical plane dynamics with the ship and tow system moving at constant heading and constant speed. The goal is to develop the Ship-Tow Interaction in Sea State (STISS) model to determine, for e.g. whether the tow system can be winched in / out without interacting with any part of the transom. STISS makes it possible to decide for a given tow system what ships of opportunity can be used as the tow platform based on only static characteristics of the tow, the tow depth as a function of scope and speed, ship transom geometry, and the ship RAOs. A unique blend of model scale tests and numerical modeling is used to help develop the STISS model. Semi-captive scale model tests of the ship with a deployed tow system were performed in a flume tank to provide validation data for up to 10 knots full scale. The partially validated STISS predictions appear reasonable and the model is awaiting full scale validation. The ability to make predictions for this complex tow condition has not been reported in the literature.

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