Waves, the wind’s assassin

There’s a discussion underway on the YBW forum about rogue waves, wave height and frequency. Here’s my take on the subject from a few years ago…..

It’s been pretty windy around here for the past couple of weeks. We’ve had Force 10 and 11 a couple of times. Off Donegal they measured a wave at 67’ (20.4m), the highest wave recorded in Ireland. The Irish Met Office says the buoy that measured it is 11km off the coast, so it was generated in deep water by the persistently high winds.

I was once in very heavy weather off the east coast of the USA and there was a point at which I didn’t think the boat was going to make it up the face of a particularly steep wave. An illusion, of course, but pretty scary nonetheless.

The probable maximum height of wind waves is around 80% of the wind speed in feet. So, a 50-knot wind blowing over an area of ocean with unlimited fetch would produce a maximum wave height of about 40 feet. This height is achieved after it has been blowing for a day, having doubled in height since the first four or five hours of the storm. Further maximum wave height increase is more subdued, it takes two days to get that wave up to 50 feet in height.

All pretty scary in a small boat.