Beaufort Scale definition.

either this thread is turning into a general piss take, the scientists are getting all scientifically pedantic or I am loosing my sense of humour .......

the beaufort scale is quite simply a way of expressing information about wind speeds (speeds measured from a loose handful of numbers ) and the expected sea height/conditions found in the oceans of the world ....... just cos a force 5 says it will generate seas of x metres doesnt mean they will be of uniform height and period, it is an indication of the approximate conditions expected.

when I see gobbblydy gook blather about a 12% increase in waffle waffle it makes me smile ........ an additional 12% of say 15kts is in practice fuk all diddly squat, if you really think boating is that precise I despair at the pooled level of joint knowldge portrayed .......... and to dismiss the effect of seas in conjunction with wind on a boat/ship is a heresy.

so either I have been had and its a wind up, or most of you are talking an absolute load of bollix - IMO of course /forums/images/graemlins/cool.gif
 
You're right - lets lay this one to rest

A hypothetical wind speed will be Force 6 to the weather station, Force 8 when I'm called up on deck from a warm bunk, Force 5 is what I'll tell the crew, and Force 3 downwind with full spinnaker up as long as we don't look behind us. If hungover with an early morning start then the wind whistling through all the rigging in the marina will confirm that it is in fact a Force 10 so best to stay in bed.
 
To be fair, if you read the original post again, it is really more of a technical question than a practical one. Discussions of sea state are all very valid when talking about the effects of the Beaufort scale, bust the post asks if there is a practical or theoretical difference between wind speed and force, and I am afraid that it is difficult to answer without getting technical.

RupertW - very good - the height of applying technical gobbblydy gook blather to a practical situation!
 
I read another aspect to the question

wind speed exerts a force as was known when beaufort made his table, thats why he called the criteria needed to produce certain phenomina as a 'force'

he wasnt potificating about lbs per square inch, humidity and tempreture, he was making a list of wind speeds and effects so ppl could understand what other mariners were referring too when talking about similiar conditions.

yes - refering too is the key to what the purpose of the scale he made up

so all this bollix about increased/decreased density and temprature is just ppl pontificating about theory - anyone reading it without realising its a load of bollix might think it was important to grasp the relavence of such intricacies.

unless modern met has changed since I did it in the 60's, the beaufort scale is a method for reference to certain wind criteria - which indicates expected sea states.........

and to now read someone takes a sail down/reefs etc cos the wind reaches e.g. 18 kts - even as an illistrative point, is a pathetic way to sail (if thats the way modern sailors sail)

IMO of course
 
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either this thread is turning into a general piss take, the scientists are getting all scientifically pedantic or I am loosing my sense of humour .......

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Oh, we can get a lot more pedantic yet.

No-one has yet (after more than 60 posts) mentioned that for a given pressure gradient the wind speed is inversely proportional to density. That means that for a given pressure gradient, low-density air (whether it is because it's warm, wet or low pressure) will move faster than high-density air. The force you feel (as a pressure on the sails) depends on the product of speed squared and density; since the speed is inversely proportional to density a low density air will feel as if it has more force. But if we are comparing forces for given wind speeds, then low density air will feel as if it has less force. Unless, of course, you are measuring air speed with a pitot-static instrument as used in aircraft; with such an instrument the density effects will completely cancel out in comparing the measured speed with the force felt.

And no-one has pointed out that that superb Australian web-site is in the southern hemisphere, so that references to port and starboard tacks need to be reversed when used in the UK.

The Met Office book "Meteorology for Mariners" has an interesting paragraph dealing with the basis of the Beaufort scale.

The BEAUFORT SCALE forms the basis of wind-force estimation at sea. It was originally introduced in 1808 by Admiral Beaufort, who defined the numbers of the scale in terms of the effect of wind on a man-of-war of his day. ..... The scale itself has not changed much, however, and it seems likely that conditions which Beaufort would have described by a certain number, judged from the behaviour of a warship of his time, would be described by the same number using the modern criterion whereby the wind force is judged from the appearance of the sea.

Alright, that was written in 1977. But my copy is from a 1990 impression, and my understanding is that it is still true; the primary criterion is the appearance of the sea, not the wind speed.
 
Thanks for that!
That means that warm, wet air is lightest. Cold, dry air is heaviest.
Now all I need to do is to get my brain round all this.
 
Agree with you all....just got involved cause I was curious to know why some posters stated that a Force 5 for example could be more or less powerful depending on atmospheric conditions. And yes there are times at 18 knots when I have had to reef, and times not.
I would really like a demo however of how one can throw a ping pong ball at the same speed and force as an iron bearing.
 
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I would really like a demo however of how one can throw a ping pong ball at the same speed and force as an iron bearing.

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First find a ball bearing which is the same weight as a ping-pong ball?
 
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the primary criterion is the appearance of the sea, not the wind speed

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to determine wind speed without an anamometer, one uses the beaufort scale as a referance, one can describe the sea state by quoting the beaufort scale as its synonimous with wind speed, and when describing wind/sea conditions one uses the beaufort scale knowing a fellow mariner knows the differance between a force 5 and 8

from my practical and theoretical use of the scale, it is used in official report writing, and often supplemented with actual recorded wind speed and observed estimated sea states

at no time in my experiences at sea, have temp/humidity been considered in conjuncion with the wind speed to adjust the 'force' experienced ........ its just crass, its theoretical bollix as I have said, as we all know even a sustained wind speed varies considerably over a period of a few minutes - much more than this 'weighting' of the air makes any practical differance.

I remain unconvinced the argument about heavy and light air has any basis /forums/images/graemlins/cool.gif
 
Ah - I understand (Ithink) - is the poster talking about Force in the Beaufort sense or the PSI sense? Only he can answer this I expect.

I think most understand how the scale came about, but referances to sea state to actually measure which Beafort Force you are in is not possible, which brings you back to wind speed as the only means. Beaufort scale in coastal waters is totally different from offshore, and even offshore it can be totally different depending where you are. Presume no one is suggesting that if the water is flat is is F 1-2 but really bumpy must be 6+?

I can understand the need to maximise boat speed for racers by working out which is optimal for all conditions, but for the rest of us it is usually other factors which have a greater bearing - do I hve young children on board; is my cup of tea still hot and full; how long will that dirty cloud take to get here; what is the forecast for the next few hours; what time does it get dark etc.etc.

Not sure that the origianl post was as prctical as this.
 
the greatest misunderstanding comes from the difference between brown water sailing and blue water sailing

the scale works in blue water /forums/images/graemlins/grin.gif and is very good at giving an indication of the wind speed in those areas

however most sailors now have an anomometer, and refer to that instead of using the eyeball and scale as was intended

small boat champ (nigel to most) remembers the days we used it as the only reliable reference ........... metoc ships were issued with hand held anomometers but these were very unreliable

in conclusion, the scale is good, works but has lost its relavence in todays marine enviroment to a greater extent. /forums/images/graemlins/cool.gif
 
I did this calculation last time this discussion came up but refrained from posting the maths that time. Basically it is an attempt to find whether the fluid density affects the speed of the anemometer cups. The first equation finds the force on the forward going and backward going cups in terms of their drag coefficients, cup and fluid speeds and the fluid density. The forces on the cups must be equal if we are ignoring friction and the cups are rotating at constant speed. The second and third expressions are the roots of the first equation in terms of the cup speed. The important point is that these roots do not contain the fluid density variable so the cup speed is independent of the fluid density.

The critical point is that wind force is proportional to the square of wind speed but simply proportional to fluid density. Variations in air density are small but variations in wind speed are large. So in practice you can ignore the variations in density. If it feels like it is blowing harder it is almost certainly blowing faster.

Sorry to be a pedantic scientist but somebody did ask for an explanation.

No, I don't think this has a practical bearing on boating but neither does a lot else that is posted here.
 
Does this mean that if I was sailing further out in blue water in a Force 7 with no anemometer and a mate was sailing inshore in brown water in identical conditions and I called him to say' It's blowing a force 7 here' he would be justified in saying ' well it's pretty calm in here, no more than a 5' and he could well be wrong ??? Do we downgrade bluewater force for brown water or vice versa if you knw what I am getting at ???
 
Understood. Makes sense anyway - unless there is something funny areodynamical gong on you wouldn't expect it to change with density.

Leon - Quite so. Sea state is subjective and not empirical. Where 'sea state was a good measure of the wind speed' - how was this known if the wind speed could not be measured accurately!?

It is all pretty irrelevant given inaccuracies in measuring equipment, and as said earlier the height at which the readings are taken (I believe it should be 33feet up, or something like this, for some reason?).
 
if he is estimating the wind speed by using the sea state on the scale, it is probably unlikely he will think is the same as you. however there are modified indicators for use near or on land ........ like this

but your mate in brown water will be influenced by tide, current, water depth and fetch - this would alter the surface appearance thus distorting the ability to accurately estimate the wind speed.
/forums/images/graemlins/cool.gif
 
Blimey .... it does go on !!

Beaufort scale is for use away from land and shallow water influences ......

It was tabulated well before anyone could actually accurately measure wind speed - using visual reference. QED

No need for science / air density / temp. etc.

If anyone cares to look at various tables of sea state / appearance and wind - there are coastal, inshore and offshore nowadays which give significant differences in text.

Landaftat - you and I will continue to look upon the waters and say ..... blimey its F8 .... F1 today .... b*****r putting up sails today !! Others will say its xx knots .............. !!!! /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif
 
feeling prickly today ?

yeah - getting fed up with it myself ...... but keep getting lured back to the thread for some reason /forums/images/graemlins/cool.gif

must get out more /forums/images/graemlins/grin.gif
 
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