How often have you been closed out by freak waves or a set? Believe it or not, there is a set rule by which you can tell how high a wave will be at a particular time.

Waves are formed out at sea (obviously). They begin from tiny ripples.

Once a “wavelet” has been formed (i.e. a ripple more than .67 in. high) it is governed under the same laws as the mighty seas into which it may grow. Its effect on the wind is to produce an increased pressure on the wave’s back or windward slope and a reduced pressure on the leeward slope, where the wind forms an eddy in the trough. The wave is at once pressed from behind and pulled in front.

The main cause of high seas is the wind strength and how long is blows. To give you an idea, after two hours of near galeforce winds (around 32 knots) on the open ocean, waves will have reached 41/2 ft. (1.44m.) and after 6 hours up to 8ft (2.56m).

After 24 hours when they’ve reached 14ft. (4.48m.) there is little increase. They may increase by less than a foot in the next 12 hours.

Wave heights, in the open ocean, of 30 ft. (9.6m.) from trough to crest are unusual and 50 ft. (16m.) waves are rare. However the American ship Ramapo made a reliable record of a 108 ft. (32.4m.) wave encountered in the north Pacific on February 7, 1933!

Waves of great height are the product of persistent hurricane strength winds raging over wide stretches of ocean.

As surfers, we’re more interested in swell than in open ocean waves, but a swell is formed as a direct result of storms.

The waves already described are left behind by the storms.

These waves keep moving (not the water – remember those physics’ lessons!) and gradually straighten out and become even as they travel through calmer water with possibly (hopefully!) a light breeze blowing the other way. Eventually they may reach land, and depending on how far they’ve come and how they’ve been refracted (bent around a point into a bay or something), then they’ ll be a part of a big swell or a small one.

People will tell you that every seventh wave is bigger than the rest. In his escape, Papillon dived off Devil’s Island using this theory to avoid being smashed on the rocks. This may be true with some swells but the pattern can vary from four to 14.

These bigger waves are caused by one swell coming into phase with another swell pattern – a joining of waves to form one big one.

Experts say that one in every 23 waves is twice the height of the average wave; one wave in every 1175 is three times the height, and one wave in every 300,000 waves is four times the average wave height. (By the way 300,000 waves would mean staying in the water for a month!) So if you want to start counting out in the line up you’ll be able to beat all the other guys to that freak. Perhaps a waterproofed calculator would help.

Footnote: Compiled from Volume 121no. 2459 of Motor Boat and Yachting article by Bill Bevis.