Decisions to make the Rudder for M/Y "Molecule" wih the fore mentioned Area calculations.
The maximum Rudder height is limited to 610mm.
The ratio between the average height of a Rudder and the average length is called aspect ratio. A tall and narrow rudder is more effective than a low and long rudder. In general, it appears that because of the limited draft of yachts an aspect ratio of 1.29 to a maximum of 2 the best choice.
For a bit aspect ratio of the rudder, I opted for a length of 420mm. The ratio is then 610 : 488 = 1.25
The balance portion may not exceed 20% of the rudder surface, the pressure then remains positive.
The area of the rudder is (598 x 610)/100 = = 3648cm² == 0,36m²
Rudderarea is (488x610)/100 = 2977cm² = 0.2977 m²
The balance part is (110x610)/100 = 671cm² = 0.0671 m²
The balance portion is 19%
The client is very happy with his new rudder.