Exploration of a systems and control approach to reduce propeller cavitation in a seaway

Dramatic increases in the underwater acoustic signature of ships have been observed during full scale trials in a seaway, compared to calm water conditions. The observed behaviour can be explained by the interaction of waves, wake field and ship propulsion system dynamics in combination with rudder action and ship motions. This paper explores whether a propulsion control system can increase the cavitation free time when sailing a straight course in a seaway. While in the past non-linear simulation tools have been used to analyse propeller cavitation in a seaway, the original contribution of this paper is that it considers the problem from a systems and control point of view. It is shown that the objective of significantly increasing the cavitation free time while simultaneously preventing thermal overloading of the diesel engine cannot simply be met by adjusting engine speed governor settings. It is however concluded that the developed plant and disturbance model are promising tools for advanced controller development and tuning aiming to reduce underwater acoustic signature.