| 摘要 |
PROBLEM TO BE SOLVED: To enable propellers to automatically return to the upper rocking position after being hit by an obstacle and rocked rearward. SOLUTION: At the rear parts of propeller shafts 11 and 19, a plurality of propellers 12 (12A, 12B) are provided and a base 12a is rockably supported by a pin 2 so that they can rock between upper and rear rocking positions. A cam 12b is formed at the base 12a of each of the propellers 12 (12A, 12B). Energization means 22 and 23 that press each cam 12a and energize each propeller 12 (12A, 12B) to the upper rocking direction are provided to the propeller shaft 11 and 19. COPYRIGHT: (C)2003,JPO
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