Marine Glossary

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wind pressure

The force of the wind per unit area. Scientifically, it would be the force on a unit area caused by the wind blowing straight onto it. This is given roughly by Wp = 0.005 x V x V in pounds per square foot, when V is in knots. More precise expressions would depend on the air temperature and actual nature of the surface. To get our derived value, start with the defintion Wp (Pascals) = Rho x V x V, where Rho is the density of air (1.25 Kg/meter cubed) and V is in m/sec.

If the air is flowing around the object then there is an additional term to account for the reduced pressure behind it, which in turn depends on the shape of the object.

At high wind speeds, the effective force of the wind is often more determined by the negative forces created by the reduced pressure caused as the wind blows across a surface more than it is by the wind blowing straight onto a surface. Damage to buildings in a hurricane, for example, are often done by this negative pressure. A roof can be "pulled off" the top of a building as likely as being "pushed in" by the wind. The same considerations apply to structures on vessels in very strong winds.

The term wind force is also associated with the Beaufort scale of "wind forces," but this is a misnomer as discussed under Beaufort Scale.