Tradeoffs in ship propulsion control - engine overloading and cavitation inception in operational conditions

Off-design conditions can have a severe impact on ship propulsion system behaviour. Resistance increase for instance leads to a higher engine loading, and can also easily lead to a decrease of cavitation inception speed with respect to calm water conditions. Wakefield variations due to ship motions, waves and manoeuvres also have effect on engine loading and on cavitation inception speed. This paper shows that one single pitch-shaft speed relation not always results in favourable propulsion system behaviour in the great variety of ship operating conditions. It is demonstrated that with relatively simple changes to the propulsion control system, the adverse effects of off-design conditions can be counteracted by using a condition dependent pitch-shaft speed relation.