| 摘要 |
PROBLEM TO BE SOLVED: To provide a small planing boat that can produce a high horsepower in a high engine speed range even when mounted with a fourstroke engine, in a small planing boat limited in length. SOLUTION: The small planing boat is so designed that water pressurized and accelerated by a waterjet pump P driven by the multicylinder four-stroke engine E with an even number of cylinders disposed in an engine room is jetted from a rear jet to cause the reaction to develop propulsion. Pairs of exhaust passages 1A and 1D, and 1B and 1C connected to exhaust ports of respective pairs of cylinders adjacent on an ignition timing basis are collected into respective single primary collective exhaust passages 2A and 2B, and the primary collective passages 2A and 2B are collected into a secondary collective exhaust means 3.
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