Windage area

Windage area is the projected area of the ship above the waterline onto a transverse or longitudinal plane, used to compute wind force and moment for maneuvering, mooring, and stability. The lateral (broadside) area drives the heeling moment in the IMO weather criterion and the side wind force in berthing and dynamic-positioning loads; the transverse (head-on) area sets the added wind resistance underway. Wind force scales as 0.5 times air density times the drag coefficient times the projected area times wind speed squared, with the drag coefficient depending on the superstructure shape and wind angle. A high-windage ship (car carrier, container ship) is hard to handle in strong beam winds, and its lateral area enters the severe-wind-and-rolling stability check.