wind and waves

The relationship between the wind and the waves is very important to boat skippers.

So important that a completely new classification system was designed as a guideline incorporating both wind speed and the wave conditions most readily found at those speeds.

Beaufort Scale

The system, called the Beaufort Scale, was developed in 1805 by Admiral Sir Francis Beaufort of the British Navy. It is, to this day, a guideline for what can be expected in certain conditions and a weather classification system.

It assumes open ocean conditions with unlimited fetch.

ForceWind SpeedDescriptionSea ConditionsWaves
00CalmSmooth, like a mirror.0
11 – 3 knotsLight AirSmall ripples, like fish scales.1/4′ – 1/2′
24 – 6 knotsLight BreezeShort, small pronounced wavelettes with no crests.1/4′ – 1/2′
37 – 10 knotsGentle BreezeLarge wavelettes with some crests.2′
411 – 16 knotsModerate BreezeIncreasingly larger small waves, some white caps and light foam.4′
517 – 21 knotsFresh BreezeModerate lengthening waves, with many white caps and some light spray.6′
622 – 27 knotsStrong BreezeLarge waves, extensive white caps with some spray.10′
728 – 33 knotsNear GaleHeaps of waves, with some breakers whose foam is blown downwind in streaks.14′
834 – 40 knotsGaleModerately high waves of increasing length and edges of crests breaking into spindrift (heavy spray). Foam is blown downwind in well-marked streaks.18′
941 – 47 knotsStrong GaleHigh wind with dense foam streaks and some crests rolling over.Spray reduces visibility.23′
1048 – 55 knotsStormVery high waves with long, overlapping crests.
The sea looks white, visibility is greatly reduced and waves tumble with force.
1156 – 63 knotsViolent StormExceptionally high waves that may obscure medium size ships. All wave edges are blown into froth and the sea is
covered with patches of foam.
1264 – 71 knotsHurricaneThe air is filled with foam and spray, and the sea is completely white.45′

When a wave system meets a current flow one of two things can happen. If the wind and current are both going the same direction, it tends to smooth out the waves, creating long swells.

If the current and wind are moving in contradicting directions, it will create much steeper and more aggressive waves.


So, what does all this mean? Why is it important to know how waves are made?

You can determine several things from waves.

One of the things you can tell based on waves, is boat speed.

This assumes that your vessel is a displacement ship, like a keelboat, and not a planing one like a speedboat.

When sailing a displacement vessel, the boat is constantly displacing a large chunk of water as it moves along. The heavier the boat, the deeper the trough it carves through the water.

Now, along with the physics of waves we discussed above, we can add that the faster a wave travels, the longer it is. As a boat’s speed increases, the number of waves that it pulls along the hull decreases until the boat is actually trapped between the crest and trough of a single wave that it has created itself moving through the water.