RUDDER ROLL STABILIZATION SYSTEMS
Rudder Roll Stabilization (RRS) is a technique which uses the vessel's rudders to simultaneously steer and counter roll. This eliminates expensive and vulnerable roll fins and cross axis coupling in which the roll fins degrade steering accuracy by pulling the vessel off heading when attempting to counter roll. A very fast rudder movement and robust steering gear are required due to the high duty cycle. These features are inherent to Autonav rotary vane and pumpset designs.
Autonav RRS was developed in cooperation with the Canadian National Research Council.
Rudder use to control heading and reduce roll achieves roll control with:
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Low frequency motions to control heading
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High frequency motions to reduce roll
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Low and High frequency corrections are independent of each other under optimal control
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Autonav control systems minimize cross-axis coupling between steering and roll (especially evident when steering and roll fins are designed separately).
The advantage of Non-Minimum Phase (NMP) Behaviour of Rudders
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The inertia-resisting movement in the yaw is much greater than inertia resisting movement in the roll
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Initial response to a “step” rudder input will produce an initial roll in the direction of the input (“faster” dynamics in roll than yaw, acting upon high frequency)
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Steady state response in roll as heel is opposite to rudder direction; slower hydrodynamics induced in yaw resistance dominate.
