Abstract: A boat has a catamaran hull with a pair of outrigger floats supported at opposite sides of the hull on support arms telescopically slidable within tubes extending across the interior of the hull for displacing the floats between extended and retracted positions. Opposite sides of the hull have recesses with shapes complementary to inner sides of the floats to allow the floats to nest snugly in the recesses on retraction of the floats. When the floats are retracted, the hull and the floats form a composite streamlined hull surface contour. The floats are shaped to produce aerodynamic thrust directed towards the hull when the floats are extended.