Assessment of the minimum speed requirement in safe return to port
The present paper discusses the aspects of how to assess the compliance of cruise ships and RoPax ferries with the requirement for Safe Return to Port as detailed in SOLAS Ch. II-2/21.4.1 – Propulsion. Part of this requirement is the necessity to be able to maintain a minimum sustained speed of 6 knots in Bft 8 weather conditions, for the worst single compartment damage case. This worst damage case is typically failure of one shaft line or engine room. The present paper discusses these methodologies applied to a 120m expedition cruise vessel. In addition, it presents the sensitivity of this requirement to exact environmental conditions, to the choice of blocked or water-milling propeller and to the ship design speed in calm water. In particular, it is demonstrated that for relatively small and slow passenger ships, the SOLAS requirement may necessitate to increase the intended onboard power.