4.2 Expression of interaction factor aH

　

 aH, XH and 1-tR indicate the interaction factor between hull and rudder. They are described by following formula,

　

 In this section, aH that make big effect on maneuvering motion is discussed.

 XH shows constant value over all propeller loading that is -0.4〜-0.5L. On the other hand, aH shows the change due to propeller load. aH increases according to the increment of advance ratio and settle to constant value after self-propulsion point. The effects of aH are discussed. One of them is taken propeller loading into account, the other is constant value that is defined at model point.

 Fig. 7 shows turning motion under rudder angle 30 degree Dotted lines indicate the estimated value by applying ah as function of Jp. The broken lines indicate motion by constant aH.

 Right after steering rudder, Jp became big because flesh water flow into propeller position and aH become larger. By this reason, FN becomes large. As the flow velocity at propeller position becomes small, aH becomes small. In this case the difference between both estimation methods are small. However, it will be big difference when the speed and/or propeller revolution are made big change.