Sea State

[Keith Hart]

Hi there

Not being a person afraid to ask a dumb question, here goes again...

I have been looking at the inshore weather forecast and see the sea state described as 'smooth, moderate, slight etc. I have a mental picture of this BUT, (you are ahead of me here aren't you?) what exactly does this mean? Where can I find the actual definitions of the sea states?

Cheers

Keith Hart (SBS)

Small boat Section

[dimitris]

Hi Keith,

I am quoting from Peter White's book "Powerboating The RIB and Sportsboat Handbook"

Wind Speeds

Beaufort Force General Description Speed (Knots)
0 Calm Under 1
1 Light 1 - 3
2 Light 4 - 6
3 Light 7 - 10
4 Moderate 11 - 16
5 Fresh 17 - 21
6 Strong 22 - 27
7 Strong 28 - 33
8 Gale 34 - 40
9 Severe Gale 41 - 47
10 Storm 48 - 55
11 Violent storm 56 - 63
12 Hurricane 64 and over


I think you should get a copy of the book. I found it very useful.

Regards

Dimitris

[Alan Priddy]

Or... Smooth..... time to look for the nearest pub on route and have a beer or two
Moderate...........Take your wown beer beacuse it is going to take longer to get there.
Rough.........It is going to hurt and everone on board is going to moan at you.
My advice is to keep your friends and family and only go out in the "smooth forecast"

Alan P

[Garygee]

There is a diference between sea state and wind speed.
The values Dimitris has given are wind speed against the Beaufort scale
Sea state while often linked with wind speed does not always work that way. Conditions like wind against tide can cause a rougher sea state and wind with tide can make things smother.

Other factors like, if it has been rough recently can also affect sea state toghther with the type of botton and depth of water.

But to answer you initial question I dont know where it states smooth as XXX and rought as YYY etc.

I will do some digging and find out what equates to what

Regards Gary

[Keith Hart]

Ah, perhaps it was not such a dumb question after all then. I imagined that there would be some sort of classification eg:
Smooth = no waves
Slight = waves up to 10cm
Moderate = waves up to 50cm
etc etc.

I was thinking along the lines of the classifiaction of my little boat (class C etc.) which started the thread 'inshore'.

I've had a look at the met weather forecast site but no luck there. I suppose we may have an answer here within a couple of days.

Awaiting with baited breath.

Keith Hart (SBS)
Small Boat Section

[John Kennett]

I can't find this information either! It's not on the Met Office web site, so I've emailed them -- I'll let you know what they come up with.

John

[Alan]

Funnily enough I was reading about this last week whilst studying an inshore waters forecast! If you have a stanfords chart the info is printed on the back (or it may be an Imray one).

Keith is correct that the sea state relates to wave height in metres. I can't recall the exact definitions but seem to recall that rough was 4m or so. That'd be fun enough for me!

Alan

[sasa]

First of all, I don't know the answer either. But I would like to know.
Also, when reading nautical magaines I sometimes read about Sea State 3 or Sea State 5 or whatever. So there seems to be yet another classification.

A while ago, while looking for material for my site I stumbled across a great series of photos showing sea states at various wind speeds (F0-F12). The photos were on the site of the National Weather Service, but I can't find them now.

Luckily, I saved them on my hard drive and have now uploaded them. You'll find them here:

http://hem.bredband.net/sansej/temp/bforce0.gif
http://hem.bredband.net/sansej/temp/bforce1.gif
http://hem.bredband.net/sansej/temp/bforce2.gif
http://hem.bredband.net/sansej/temp/bforce3.gif
http://hem.bredband.net/sansej/temp/bforce4.gif
http://hem.bredband.net/sansej/temp/bforce5.gif
http://hem.bredband.net/sansej/temp/bforce6.gif
http://hem.bredband.net/sansej/temp/bforce7.gif
http://hem.bredband.net/sansej/temp/bforce8.gif
http://hem.bredband.net/sansej/temp/bforce9.gif
http://hem.bredband.net/sansej/temp/bforce10.gif
http://hem.bredband.net/sansej/temp/bforce11.gif
http://hem.bredband.net/sansej/temp/bforce12.gif

(Sorry for posting all the links, but the server does not allow listing of the directories.)

The above descriptions are only valid at open sea, where there is enough of distance for the waves to build. Also there is a minimum of time the wind needs to blow. There are diagrams that can be used to predict wave height given wind speed, time duration and stretch of open water.
And, as Gary already said, there is a number of other conditions that influence the sea state.

I know this is not an answer to your question, Keith, but I hope it is a step in the right direction.

Sasa

[Allan]

Here is my attempt to reduce things to a basic description; I can't figure out how to lay out a table in here (it was looking great till I previewed it) so I hope that the information will make some sense!

The info is laid out as follows: first is the Sea State number followed by the description for that state, then an approximate wind strength for that sea state and the final figure in brackets is the average wave height. I did not attach a wave height for states 0,1 and 3


0 Calm Glassy, force 0
1 Calm Rippled, force 1 and 2
2 Smooth wavelets, force 3 ( 2 feet )
3 Slight, force 3 to 4
4 Moderate force 4 to 5 ( 5 feet )
5 Rough force 6 ( 9 feet )
6 Very Rough, force 7 ( 14 feet )
7 High, force 8 ( 23 feet )
8 Very High, force 9 ( 31 feet )
9 Phenomenal, force 10-11-12 ( 54 feet )

The sea states do not exactly co-incide with the wind strengths (that would be too easy) and the wave heights are the suggested average for the Nominal Sea State, obviously with a fairly significant difference in windspeed covering a given sea state, the wave height will be far less at the bottom end of the range than the top.

What I have put here is trimmed to the minimum (always risky!) but perhaps gives some idea of what is involved, I found an excellent table with the relevant data laid out very clearly at http://www.seathree.demon.co.uk/seastate/index.htm

[dimitris]

Allan,

Your link summarizes very nice sea states.

Keith, sorry for giving you a misleading or half answer. The Book is nice though.

Allan P, any particular brand of beer that goes with sea states ?


Regards

Dimitris

[Garygee]

Great link Allan I will be saving this one.


Regards Gary

[Keith Hart]

What? Moderate, waves!!! 5 foot

I had the vision of small waves lapping gently at the side of my boat whilst I gently cruised between the islands gazing at seals and dolphins for MODERATE.... Mind you PHENOMENAL sounds fun!!

Well, it just goes to prove how useful and educational this forum is to us new commers. Thanks for all the info, just what I needed.

Cheers

Keith Hart

[Garygee]

When looking at wave height a very important factor is the wave interval. You might find that 10 foot waves with a long wave interval just gives you a big rolling sea which you can just go up and down at quite some speed. almost like a big dipper effect
On the otherhand a 3 foot wave with a very short interval may give you quite a pounding.
At open sea the wave intervals tend to be much longer getting much shorther as you come inland or shallow water.
I have often been out with a six foot wave height not far of Milford Haven and while seeing the waves above you may be a but unnerving as they do not break the only real risk if seeing your last meal again.





Regards Gary

[Powerboat]

Hi ,

The following which can be found in the RYA Powerboat Course notes manual ( standard issue to all ISA / RYA Level 2 students is :

1- Light air ripples
2 - Light breeze small ripples
3 - Gentle breeze - somebreaking wave crests
4 - Moderate breeze fairly frequent white horses
5 - Fresh breeze many white horses some spray
6 - Strong breeze extensive white horses and spray
7 - Near gale very rough foam streaking down wind from wave crests
8 - Gale
9 - 12 Stay at home !

I also have another more detailed version in another book which I read recently ( but damned if I can remember where ! ) which in addition makes reference to the amount of canvas a smack can carry in the various wind strenghts !

Best wishes ,

Stuart
www.powerboat.org

[John Kennett]

I've had a reply from the Met Office customer support department who say they don't know but will find out!

Watch this space for the definitive (!) versions of smooth, moderate and rough . . .

John

[sirzap]

No matter smooth or moderate, I always feel rough in the morning...

[LamacqS]

Just to throw in what the admiralty say:


Code Description Height (metres)
0 Calm-Glassy 0
1 Calm-Rippled 0 - 0.1
2 Smooth wavelets(?) 0.1 - 0.5
3 Slight 0.5 - 1.25
4 Moderate 1.25 - 2.5
5 Rough 2.5 - 4
6 Very Rough 4 - 6
7 High 6 - 9
8 Very High 9 - 14
9 Phenomenal 14+

[batfalcon]

I think that we all sail with force 0 to 5 (max). If by any bad chance get caught in sea with force 6 or more, I am sure that none of us will really cares what the waves height was.
Does anybody cary a measuring tape on board ?