PURPOSE: To provide a power-propelled coaster boat which can coast at a high speed on the water surface always in the stable condition by installing a prime mover at the head or tail of the second and the third barrel functioning as a float and fuel tank which are arranged symmetrically on the left and right about the first barrel where the driver gets on.

CONSTITUTION: With the first barrel 1 as the center where the driver gest on, the second 2 and the third barrel 3 are arranged symmetrically on the left and right as functioning a float and fuel tank. Two couplings fore and aft 5, 6 are used for coupling the first barrel 1 with the second 2 and the third barrel 3. To lessen the resistance receiving from the water, the front or the whole of the boat must be put afloat, and therefore, the couplings 4, 5 and flaps 10, 11 have a section similar to the wing of an aircraft.