Cross section of Rupas®

Its radius of the rudder front section is smaller and its rear shape has hollow with parallel shape, comparing with the conventional rudder section. This provides higher lift and also smaller rudder resistance at midship rudder angle than ones of the conventional rudder.

Rupas® Conventional

Rupas® for the actual ship

Working force on the rudder

When steering in the propeller flow with rudder angle of δ, the normal force of Fry happens on the rudder as shown below.
Its quadrature component to the ship is the lift, and parallel component is the resistance.
This lift makes ship turning.

Rudder normal force and rudder resistance

The left figure compares the normal forces of Rupas® with ones of conventional rudder at each rudder angle. It is found that Rupas® generates a normal force approximately 12% greater than one by conventional rudder at the same rudder angles.
The right figure compares the rudder resistance of Rupas® and one of conventional rudder at midship rudder angle. It is found that the rudder resistance of Rupas® is slightly less than one of conventional rudder.

Comparison of normal forces on Rupas® and conventional rudder

Comparison of rudder resistant on Rupas® and conventional rudder

Actual Rupas® installed on a vessel

Below is a study of replacing Rupas® with a conventional rudder. Left figure shows that a rudder area becomes approximately 12% less, because Rupas® increases the normal forces. Right figure shows the results of Zig-zag model test of Rupas® and conventional rudder, where it is found that Rupas® with smaller rudder area has slightly better maneuvering performance than conventional rudder.

Shape of Rupas® and conventional rudder

Results of the Zig-zag model test equipped with Rupas® and conventional rudder

Rupas®：Rudder with Parallel Section at trailing part® is a registered trademark of Japan Marine United Corporation. Unauthorized use is prohibited.