Abstract-An anti-spin controller for marine propulsion systems in rough seas is developed. From measurements of motor torque and propeller shaft speed, an observer providing an accurate estimate of the propeller load torque is used to calculate an estimate of the torque loss. A monitoring algorithm utilizing the estimated torque loss detects ventilation incidents, and activates the anti-spin control action. When a ventilation situation is detected, the anti-spin control action will reduce the propeller shaft speed to some optimal value, using a combined power/torque controller. The ultimate goal is to minimize the effect of ventilation, and hence increase the thrust production, limit the transients in the power system and reduce the mechanical wear and tear of the propulsion system components. Simulations are provided to validate the performance of the control scheme.

Results from laboratory experiments with an electrically driven propeller controlled by three different control systems are presented, showing the advantages of torque and power thruster control over shaft speed control. For fixed pitch propellers, the industrial standard today is shaft speed control based on a static mapping from desired thrust force to desired shaft speed. When the operating conditions change due to vessel motion, waves and current the propeller loading changes. The results are fluctuating thrust production and load torque, which lead to mechanical wear and tear and unpredictable power consumption. This may lead to severe deterioration of the performance of a vessel; the power fluctuations force the operators to have more generators running than necessary, and the mechanical wear and tear lead to vessel down-time due to repairs. Alternatives to shaft speed control are torque and power control, based on static mappings from desired thrust to desired torque and power respectively. This paper demonstrates by experimental results that significant performance improvements can be achieved by changing to torque or power thruster control.