| 摘要 |
PROBLEM TO BE SOLVED: To hold down the frictional resistance of a propeller to the minimum by building a counter-rotating mechanism in a lower case, forming an exhaust passage in a boss part of at least the front propeller, and communicating the exhaust passage with an exhaust passage formed in the lower case. SOLUTION: A solid inner shaft 5 and a hollow outer shaft 6 which form an inner and outer double shaft are disposed below a lower case 4, and a rear propeller 3 and a front propeller 2 are connected respectively. An exhaust passage 9 is formed in a boss part 2a of the front propeller 2. An exhaust port 12 for discharging exhaust gas flowing through the exhaust passage 9 underwater is disposed between blades 2b of the boss part 2a. The exhaust gas from an engine is passed through the exhaust passage 10, some of the gas is discharged from a gap 11 to be entangled in the front propeller 2, and the remainder is let flow through the exhaust passage 9. Some is discharged form the exhaust port 12 to be entangled in the front propeller 2, and the remainder is discharged from a rear end opening part of the exhaust passage 9 to be entangled in the rear propeller 4. |
