| 摘要 |
PURPOSE:To exhibit the effect of a fin so as to increase the propeller efficiency by providing a boss cap having plural fins on the propeller rear part of a propeller propulsion unit, and providing two rudders on symmetrical positions of the right and left gunwale sides of the propeller in the rear of the propeller propulsion unit. CONSTITUTION:A boss cap 3 in the rear of a propeller 2 in a propeller propulsion unit 1 is provided with small fins of the same number as the number of those of the propeller. Two rudders 5,5 are provided on the right and left symmetrical positions about the center M of the propeller in the rear of the propeller propulsion unit 1. The distance BX2 between both rudders 5, 5 is suitably set according to the diameter D of the propeller 2 and the condition of the slip stream. The fin 4 rectifies the slip stream of the propeller boss part to prevent hub vortex cavitation and recovers the swirl current energy to lessen the propeller torque and improve the slip stream of the propeller in the vicinity of the center M of the propeller. As two rudders 5, 5 are outside of the basin where the propeller slip stream is contracted, the resistance is small. |
