| 摘要 |
PURPOSE:To prevent intrusion of cooling water into a combustion chamber by having a cooling water jacket provided around an exhaust expansion chamber communicated to the position on the exhaust lower stream side from an exhaust introduction part in an exhaust passage. CONSTITUTION:Cooling water having passed a water jacket 33 of an engine 12 passes in water jackets 50-53 and cools an exhaust box 35. At this time, the water jackets 50-53 are communicated to each other, and the cooling water is discharged from an exhaust introduction part 54 of an exhaust passage 46A through a communication part 55 in the middle of the exhaust lower stream side to an exhaust passage 46B without passing through an exhaust expansion chamber 45. As the exhaust introduction part 54 is located upper than the communication part 55 in this way, drain can be prevented from being dragged or flown into the exhaust expansion chamber 45 or the engine 12 because of exhaust pressure wave, posture change of a boat body and so forth.
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