Jet-propulsion watercraft

A jet-propulsion watercraft comprising:

• an engine having a cooling water passage inside thereof and cooled by cooling water;
• an exhaust passage extending from the engine and having a double-walled structure comprised of inner and outer walls between which a cooling water passage is at least partially formed, for discharging an exhaust gas;
• a water jet pump driven by the engine, the water jet pump pressurizing and accelerating water taken in from outside of the watercraft and ejecting the water from an outlet port to propel the watercraft as a reaction of the ejecting water, and supplying part of the water to the cooling water passage of the engine and the cooling water passage of the exhaust passage;
• a water-supply hole formed in the inner wall of the double-walled structure, for supplying the water into an exhaust gas passage in the exhaust passage;
• a first cooling water passage for supplying the cooling water to the cooling water passage between the outer wall and the inner wall of the double-walled structure;
• and
• a bypass passage formed independently of the first cooling water passage, for supplying the cooling water to the cooling water passage between the outer wall and the inner wall.