PURPOSE: To prevent water drained out of a rear deck, from flowing into a cabin and improve the properties of dwelling in the cabin, by making the floor of the cabin lower than the water line, making the rear deck higher than the water line and providing a wall between the cabin and the rear deck.

CONSTITUTION: The floor 4 of a cabin 1 is placed lower than the water line 9 so that a large space is provided in the cabin. A rear deck 3 is placed higher than the water line 9. A wall 50 is provided on the front of the rear deck 3. A seat base 5 is provided on the wall 50 so that water staying on the rear deck 3 is kept from flowing into the cabin 1. A roof 2 is provided over the cabin 1. A cover 7 can be easily fitted in the rear opening of the roof 2 by using hooks 71 provided on the edges 70 along the opening.