Control of propeller cavitation in operational conditions

Off-design conditions can have a severe impact on ship propulsion system behaviour. Resistance increase, for instance, leads to 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 an effect on engine loading and on propeller cavitation. This paper discusses the model-based development of a propulsion control system aiming at increased cavitation free time in operational conditions, while preventing engine overloading and keeping manoeuvring characteristics acceptable. The developed propulsion control system was tested extensively in a simulation environment before full-scale trials took place in February 2008, onboard a Royal Netherlands Navy frigate. Results in terms of full-scale propulsion system behaviour are presented, including photos showing the propeller cavitation behaviour in operational conditions.