JET-PROPELLED BOAT

摘要

The expected performance of a jet-propelled boat is maintained, exhaust control valves are controlled and driven in an improved accuracy on the basis of the traveling speed of the jet-propelled boat, fuel consumption is improved and the exhaust gas is purified. A two-stroke cycle engine 9 drives a jet propulsion unit 10 to make the jet propulsion unit 10 sucks in water and jets water to propel a hull 1. An exhaust control valve 40 is disposed near the exhaust port 39 of the engine to change the opening ratio of the exhaust port according to the operating condition of the engine. A driving mechanism for driving the exhaust control valve includes a hydraulic actuator 55. The power of water jetted by the jet propulsion unit 10 represents the traveling speed of the jet-propelled boat accurately. The exhaust control valve 40 is driven for opening and closing according to the pressure of water jetted by the jet propulsion unit 10 to achieve the optimum exhaust control by the exhaust control valve without entailing the excessive increase in the output of the engine 9.