Windage

The aerodynamic force or effective exposed area through which wind acts on a vessel and its equipment.

Hull topsides, superstructure, rig, sails, covers, deck cargo and people contribute according to projected area, shape, height and wind angle. Windage affects leeway, low-speed manoeuvring, anchoring and mooring loads even when the vessel is not moving through the air under its own power.

The term is often used loosely for either area or the resulting drag, which should be distinguished in calculations. Gusts, shielding, heel and the height of the centre of pressure alter both force and turning moment.