Patent ID: 6886485

Claim:
A twin-rudder system for very large vessels in a high lift twin-rudder system, said system comprising: a single propeller having a propeller axis and a diameter; a pair of high lift rudders arranged behind said single propeller nearly parallel in a symmetrical position against the propeller axis; each high-lift rudder having a rudder blade having: a blade chord length; a top end plate and a bottom end plate; a horizontal sectional profile having a forward protruding semicircular leading edge portion having a tip, a mid body portion continuative with the leading edge portion, said mid body portion increasing in width up to a maximum width portion in streamline shape, and then gradually decreasing in width toward the minimum width portion, and a fish tail trailing edge portion continuative with the mid body portion, said fish tail trailing edge portion gradually increasing in width laterally toward both boards or an outboard and terminating in a rear end face having a fixed width; a reaction fin protruding from an inboard face of said rudder blade on generally the same level with the propeller axis, said reaction fin originating from about the leading edge portion of the rudder blade and extending toward the fish tail trailing edge portion, said reaction fin having a blade section having a fixed fin chord length; wherein said blade chord length of each rudder blade is between 45 and 60% of said propeller diameter, and wherein fins are appended on a propeller boss cap for making the propeller boss cap generate a stream in the same direction as a propeller slip stream generated by propeller blades.