The concept of anti-spin thruster control

Experimental results for a ducted propeller with varying submergence and loading at low advance velocities are presented, and a simulation model for propellers subject to ventilation and in-and-out-of water effects is proposed. Motivated by this, the concept of anti-spin control for thrusters operating in extreme seas is introduced. Two operational regimes are defined: normal conditions and extreme conditions. Alternative thruster control schemes for normal conditions are possible: conventional shaft speed control, torque control, power control, or combinations of these. In extreme conditions the thruster may be subject to severe thrust losses, which can lead to propeller racing. When such losses are detected, an anti-spin control action which counteracts the propeller racing is proposed. The anti-spin control concept is shown to give increased control of the thruster performance in extreme seas, especially when using torque or power thruster control. The results indicate that a combination of torque or power control with an anti-spin control scheme will improve thrust production, reduce mechanical wear and tear, and reduce power system transients in both operational regimes.