Ship service speeds and sea margins

When designing a transport vessel, one of the most important parameters assumed by the owner is the service speed of the ship. Service speed and motor power are calculated as an approximation of the ship’s speed in calm water (i.e., the contract speed) with the addition of the sea margin (SM). In current design practice, the addition of SM is not dependent on weather parameters occurring in liner shipping. This paper proposes a new method for establishing the value of SM depending on the type and size of the vessel and the average statistical weather parameters occurring on various shipping lines. The results presented in this paper clearly demonstrate that further research is needed to determine the precise relationship between the shipping and vessel type and the weather parameters on a shipping line.