PURPOSE: To secure such a plastic leisure boat that will not founder even in case of breakdown or being holes in the bottom, by constituting the hull with a double wall construction so as to make up a hollow part with a plastic material being excellent in rigidity.

CONSTITUTION: A boat body 1 is formed into a hollow body in a double-wall construction consisting of an outer wall (a) and an inner wall (b). This double- structure hollow body forms the stem 2, the stern 3, the bottom 4 and the boat's sides 5 and 5 as a separated hollow part each. Even if the outer wall (a) of the hull 2 gets holed due to a collision or the like, the boat is confined only to submersion inside the hollow body of this double-wall construction, thus it can escape from foundering.