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The availability of the propulsion system is of primary importance to ensure safe and stable operations of marine crafts, both during transit and station keeping. Diminished propulsion efficiency could impair the ability of a vessel to maintain speed and course and possibly lead to a drifting craft. The waterjet’s propulsion efficiency is affected by several factors such as cavitation, erosion, vibration and noise emission. This paper addresses the design of a fault-tolerant thrust allocation algorithm able to maintain the seaworthiness of a twin-waterjet marine craft in the presence of a severe power loss in one of the waterjets. The proposed solution combines a load torque estimator with an optimization routine that accounts for the power limits when a waterjet is subject to a power loss. This prevents faults from quickly escalating into a complete failure of the waterjet due to excessive power demands. Two simulated case studies including zig-zag path following and sideways movements are presented to demonstrate the effectiveness of the fault tolerant control thrust allocation strategy.

Waterjet propulsion is increasingly used in both combat and civil ships. In this study, a mechanism analysis-based modelling approach of a dual-waterjets propulsion steering system is presented. Experiments carried out on an experimental platform are used to validate the model system. Then a model-based synchronous control strategy for the dual-waterjets propulsion steering system is developed. The experiment results show that the model-based proportional–integral synchronous control strategy may reduce the synchronization error significantly compared with the reciprocal of the synchronization error driving synchronous control strategy practised on some small ships.