Thruster Allocation Logic

Where the wind, wave drift and current effects are known for a specified environmental magnitude and direction, the combined rudder and thrust requirements (, , , , ) in the longitudinal and transverse directions and yaw moment can be determined from equation (70). These total thrust and rudder force requirements in order to give a static balance need to be allocated to the individual thruster and rudder units. Clearly where there are more than three thrust units there are more unknowns than the number of equations and the problem is solved using optimal control theory in order to minimize the total thruster demand of the system. The allocation method needs to take account of thruster limits which may differ for fixed longitudinal thrusters for ahead and astern operation and, for steerable thrusters, the inclusion of barred zones of operation is included in order for you to prohibit the thruster wash of one unit being directed to another thruster.

Where a rudder is operating behind a fixed propeller this can be treated as a specialized case of a steerable thruster with a barred zone. The allocation procedure for fixed thrusters and steerable thrusters with and without barred zones is based on methods given in References 51.