PURPOSE: To achieve smooth recovery of tilted hull by forming a covered recess independently from an enclosed space formed with inner/outer boards at a portion of vessel and using it as a container under normal state while as a floating force reduction chamber upon tilting.

CONSTITUTION: An enclosed space 40 is formed between a plastic outerboard 2 and an innerboard forming a cockpit to produce the hull of yacht. The innerboard is comprised of a floor board 3 in the central portion, a seat board 4 continuous from said board 3 through a rising wall 34 and an insideboard 44 coupling between said seatboard 4 and the upper circumferential edge of the outerboard 2. The seatboard 4 extending in the longitudinal direction of hull is partially notched to form a covered recess 50 which is used as a container under normal state. Consequently, the overwater projection of hull is reduced upon tilting to reduce the inverting resistance resulting in facilitation of recovery of hull position.