It is natural to assume that if the wind speed increases from 5 to 10 mph then its force will double. But that isn't correct. The effective force of the wind actually increases 400%! If the wind further increases to 15 mph, then the effective force is 900% greater than it was at 5 mph.
The generic formula prescribed by the American Society of Civil Engineers for calculating wind load is Wind Pressure Per Square Foot x Surface Area in Square Feet, where:
Wind Pressure Per Square Foot = .00256 x Wind Velocity in MPH2
Sailors quickly learn this once they realize that sailing in 15 mph of wind is completely different than sailing in 5 mph. The difference is so dramatic that most sailors won't even venture out in winds much over 15 mph.
The purpose of this page is to provide a resource to help compare different wind velocities and predict how those changes may affect a given boat.
The Beaufort Scale is a measurement of wind velocity based on observed conditions at sea and on land. It was developed in 1805 by Francis Beaufort, a Royal Navy officer, and remains a very practical and handy means of expressing wind velocity without the need for instuments. The table below shows the 13 levels of the Beaufort Scale:
|0||Calm||< 1 knot|
|1||Light Air||1-3 knots|
|2||Light Breeze||4-6 knots|
|3||Gentle Breeze||7-10 knots|
|4||Moderate Breeze||11-16 knots|
|5||Fresh Breeze||17-21 knots|
|6||Strong Breeze||22-27 knots|
|7||Near Gale||28-33 knots|
|9||Strong Gale||41-47 knots|
|11||Violent Storm||56-63 knots|
|12||Hurricane Force||>= 64 knots|