Figure 4.3 shows the components of the force produced by the rudder. The rudder propelle has been placed with an angle of attack ® in a homogeneous low with a constant velocity V . Practically, V is de…ned as the velocity of the fluid far before the rudder. For small angles of attack, ®, the total force P on the propeller acts at about e t 0:25 ¢ c, provided that the span width s is large with respect to the chord length c. This force P can be decomposed in a lift force L perpendicular to the low and a drag force D in the direction of the low. The total force P can be decomposed in a normal force N and a tangential force T, too.
Rudder forces are made dimensionless by the stagnation pressure and the projected rudder area Ar: