The concept of the Gate-Rudder is clearly deviating from other conventional rudder systems. Single screw vessels have in general the rudder placed behind the propeller, where the movable part can be a part (semi-spade) or the complete rudder section (full-spade). The rudder profile sections can be pre-aligned with the incoming flow (twisted leading edge) or straight. On the other hand, the Gate-Rudder concept comes with 2 symmetrical rudder parts, which are placed on both sides of the propeller. The downstream, accelerated flow will thus not directly interact with the rudder.
Design of the rudder-sections targets at a stagnation point of the flow close to the outer-side of the rudder leading edge. As a consequence, a low-pressure region is created on the inner side of the Gate-Rudder, which creates a net-thrust force. Second effect of this concept is a large inward oriented force. As long as both rudder-parts are positioned at the same steering angle, the two inward force-components compensate each other. Once a small ruddersteering action is executed, the force-balance shifts, which results in the desired side-force to steer the vessel. The Gate-Rudder concept can thus be compared to a kind of pre-tensioned system. Figure 1 shows a picture of the Gate-Rudder concept with a CCP propeller, where the two symmetrical rudder-parts are clearly visible. More details on the concept and results from a comparison of two sister-vessels with conventional and Gate-Rudder can be found in paper by Sasaki et al [1].
