Open Access

Michael Vahs, Sascha Strasser, Siegfried Wagner

• Safe and effective navigating and manoeuvring of ships is an essential part of ship operation. The manoeuvrability of ships under sail differs significantly from engine power driven vessels. Ships purely powered by the wind can hardly predict their manoeuvrability as it depends on varying wind conditions and the status or mode of the wind propulsion system, e.g. full sails set or sails reefed. If a sailing vessel and an engine powered ship encounter under risk of collision the international regulations to avoid collision (COLREGs) [IMO, 1972] apply a hierarchical order of ship categories and prescribe manoeuvring action to avoid collision guided by the principle that ships with full manoeuvrability have full responsibility whereas ships restricted in their manoeuvrability are relieved as they cannot contribute effectively to avoid collision. Thus, engine powered vessels have to give way towards sailing vessels. COLREGs take the restricted manoeuvrability of sailing vessels as a fact. Pure sailing vessels have always been part of the shipping fleet and need to be considered for the objective of safe navigation and traffic flow. Differently, the manoeuvring standards for ships laid down in IMO guideline MSC.137 [IMO, 2002] are addressed to ships of any kind of rudder and propulsion with a length of 100 metres and over, and chemical and gas tankers regardless of the length. It can be assumed that MSC.137 does not consider sailing vessels for their low relevance in commercial shipping. From a regulatory view this could imply that all sailing vessels shall be suited with redundant propulsion to be operated as engine powered vessels. Thus, sailing vessels with engine propulsion can be operated in three different modes: as pure sailing vessels, pure engine powered vessels or as hybrid powered ships. There are no specific regulations and requirements on manoeuvrability of ships operated in these modes nor for the change over from one mode to another. This may turn out to be a “grey zone” for navigators on wind powered vessels of the future. This paper looks at the manoeuvrability of modern wind powered vessels in regard to regulations and practical requirements for navigation and collision avoidance. The focus is on the applicability of current regulations from the navigator’s view based on the operational experience of first modern wind assisted vessels. The legal gaps that are identified and their situational context may lead to insights and approaches for the revision of relevant rules and regulations, examples are given. The paper presents the kick-off phase of the funded “Cargo Sailing Vessel” ship design study performed by Emden/Leer University of Applied Sciences and their partners. An investigation on the manoeuvrability of wind powered ships under operational conditions is in preparation under the project’s framework.