Sea state slight to moderate

[MontyMariner]

My heart really goes out to people who get sea sick, it's got to take a lot of the fun out of sailings.

 

[ylop]

A lot of people are deceived by the word “slight” - sounds fairly benign… but it actually described waves up to 1.25m (moderate is 2.5m). Moreover, when we quote wave heights we usually are referring to a statistical “significant wave height” but that not the maximum - you should expect to sporadically see individual waves which are 3x the significant wave height. So on a crossing to the Isle of Man with forecast 1.5m waves it would not be at all surprising to see waves of 4m+.

 

[oldgit]

Have never had problem with that wind against tide short Thames chop apart from wishing had never set out , my worry is on a big vessel ie. ferry. You can feel the bow going down and down and wondering when and if the hell ,it is ever going to come up again

 

[Supertramp]

Also, there's the question of the waveLENGTH as well as wave height. A wave height of several metres is not dramatic IF the wavelength is tens or hundreds of metres. But the same wave height with a wavelength comparable to the length of our boats is horrible! Of course, wavelengths shorten as waves get into shallower water - compare the North Sea chop with the West Coast of Scotland where waters are generally much deeper. When bringing Capricious from the Clyde I really noticed the difference!

Wave height is measured by satellite's over a footprint of kilometres, so although we know the wave height, we generally don't know the wavelengths. And of course it's not that simple - there are usually several interesting wave trains, so there are complex interactions.

Wave height alone doesn't give enough information.

That's exactly right. There are enormous swells off the West Coast which are rarely any bother, unless you are out in a gale. My experience of the Irish Sea is that it can generate surprisingly steep waves in fresh winds, partly due to tide effects and partly due to the interference between wind waves and the swells rolling up from the South.

Some of my most uncomfortable passages have been the day after a fresh or gale force wind with the sea state still unsettled and at odds with the new wind direction.

Shallow water has a big effect especially on swells - things get a lot better once the water is over 20-30m deep. Cardigan Bay is a nice place to sail but very exciting in a fresh SW with a strong swell running and in 10m or less depth.

 

[Davy_S]

Looking at the vid i know it does not give a good impression of waves, but i fished in a small boat off the Fylde coast regularly in conditions like that, especially when crossing the Lune deeps, the most spectacular swells (as mentioned different to wave height) has to be fishing off Bridlington when a Northerly has blown, the swell is Huge! you are protected by Flamborough head from the worst, but there is a football pitch length in between the swell, you lose sight of all other boats when you drop down, but it is perfectly safe if a bit vomit inducing!

 

[Refueler]

That's exactly right. There are enormous swells off the West Coast which are rarely any bother, unless you are out in a gale. My experience of the Irish Sea is that it can generate surprisingly steep waves in fresh winds, partly due to tide effects and partly due to the interference between wind waves and the swells rolling up from the South.

Some of my most uncomfortable passages have been the day after a fresh or gale force wind with the sea state still unsettled and at odds with the new wind direction.

Shallow water has a big effect especially on swells - things get a lot better once the water is over 20-30m deep. Cardigan Bay is a nice place to sail but very exciting in a fresh SW with a strong swell running and in 10m or less depth.

The North Sea is infamous for this ... quick to rise - quick to subside.

 

[Daydream believer]

On well over half my sailing trips I am sea sick. Being a SH sailor for 90% of the time until I broke my Femour last October made it very difficult. I found that the electronic sea sick watch helped a bit. I usually just chuck up on the side deck & clear it up later. In August I went to Ostend for the 80th time& I think it is rare for me to go there or back without being sick. Sure enough, as I rounded the Longsand Head I started. Winds 15-28 kts. The trip back in Sept was only a little better when I just avoided it.
In 21 years I have only anchored my current yacht 5 times as anchoring sets me off in minutes. Yet I can sit on the boat in Ostend & be tossed about in a northerly with no problem.

 

[AntarcticPilot]

A lot of people are deceived by the word “slight” - sounds fairly benign… but it actually described waves up to 1.25m (moderate is 2.5m). Moreover, when we quote wave heights we usually are referring to a statistical “significant wave height” but that not the maximum - you should expect to sporadically see individual waves which are 3x the significant wave height. So on a crossing to the Isle of Man with forecast 1.5m waves it would not be at all surprising to see waves of 4m+.

Or even higher. The distribution of wave height is not a normal distribution (in the statistical sense), but has a very long tail. So "rogue waves" are commoner than naive statistics would indicate.

 

[FairweatherDave]

This is a good revision thread for me. I've just been reading about the Douglas scale, which I expect I have come accross before. As ylop says, "slight" and "moderate" are more meaningful terms than you might think. I shall try and take more notice!