Abstract
Roll-coupling effect on ship maneuvering motions is not negligible for high speed vessels, large container ships, passenger ships and so on. To perceive the roll-coupling effect on the ship maneuverability, in this paper, approximate formulas for course stability criterion, steady turning index and the response time until reaching to steady turning (time constant) in the framework of the linear motion theory were derived on the assumption where the depthwise acting point of lateral force with respect to roll moment is constant even in any modes such as oblique moving, turning, rolling and steered conditions. Using the hydrodynamic derivatives measured in tank tests for 3 ship models, the roll-coupling effect on the ship maneuverability is discussed. The course stability becomes worse with increase of Froude number of the ship and/or decrease of metercentric height in general, and the turning performance is improved and the time constant becomes long. The approximate formulas have sufficient calculation accuracy and the formulas are useful for conventionally checking the ship maneuverability.
