Beaufort Scale definition.

This makes perfect sense to me....a wind force gauged by it's effects on obstructing objects. So a 30 knot wind in a sheltered river with almost no fetch could be a force 5, but out in the middle of the north sea could be a Force 8 ??
 
I don't think you can really let fetch or wave heights come into it. A Force 5 in the open sea is still a Force 5 behind a sandbank, although there are large waves in the sea and just ripples in the shelter.

Beaufort forces can't be expected to be a "one number" measure of all the risk factors in boating, otherwise you might as well add in fog, and the amount of fuel you've got left etc. etc.
 
Couldn't agree more....just that the effects of a force 5 or any other strength can be exacerbated depending where you are which is something we all know. However if we refer to the post re Beaufort initially not being related to wind speed, what I was trying to say was that what seems like a wind speed of Force 5 in an exposed position may really only be the same speed as a 3.
 
I can see what you're saying but the force of the wind (and wind alone) on a boat or on sail will be exactly the same whether you're in sheltered water or in open water. So the wind force (mixture of mostly wind speed but also varying density) is the same regardless of where you are.

However, all the other factors may cause you to act differently in a Force 5 in one environment compared to another.

I think we're saying the same thing, I think.
 
I think there needs to be a new scale,from all accounts yachts are just getting into their stride whilst "Smacks are into the second reef having doused the topsail and run in the bowsrit!
 
Not really too complicated.

Ignore sea state. The same 30knot wind may have more or less force depending on the air pressure,temperature and amount of water water vapour. Empirically I reef earlier in the winter in an easterly than in the summer in a south westerly because the easterly has high pressure, the air is cold and dry compared to a low pressure summer SW where the pressure is low, the air is warm and full of water vapour

The sea state is entitely different and is used as a rule of thumb to gauge wind force in open water.

The actual sea state has a different scale, the Douglas scale.
 
You Brits could do as the rest of the world does and just not use Beaufort or any other such scale - everywhere else I can recall just uses knots (or metric) for wind.

John
 
Re: Beaufort Scale definition. Twister Ken has it by the nut\'s !

Exactly ....

Dear old Beau used physical observation of sea state and items around him ... ie sails etc. to define a scale of wind. The word "force" is applied more in a literay sense rather than a scientific basis.
Later "experts" added in wind speeds to help us later ij'ots to be able to use the scale better ....

I suspect Landaftat as I, will agree that on board ship when writing up a log at end of watch etc. - you looked over bridge wing / out window and estimated wind speed by the appearance of the sea-state .... then the table of speed range. If you were lucky and likely a Weather reporting ship - P.I.T.A job to watchkeepers ! - you had a wind speed and direction indicator .... which yoy basically reversed the assessment - unless sea state looked out of step !! Then many took sea-state ....

FYI ....
 
For the 2nd time in a week I agree with the 'Cat'.

The rest of the world talk about knots of wind.

I 'think' Beaufort made the scale when there was no really accurate way of measuring the wind alone so he described the conditions in open sea - so that the sea state observation backed up the wind speed estimation.

The advantage of talking in Knots is that you can have various 'reefing' times more or less set for every situation - eg - going to windward first reef in at 18k - and so on. Makes it easier.

The sea state varies with the relative shallows, currents and tidal streams and depth of the water as well as the direction of the wind against any of the above...

I think Beaufort should be put on the shelf and forgotten along with the Walker log... sadly..

Michael
 
Thanks..think I understand it now....I was caught in a nasty squall off Canvey Island over the Bank holiday. The anemometer was reading 28 apparent...however it seemed a lot more violent than the same windspeed beating into the Crouch last year, or even two years ago up by the Barrow Sands, when the wind was up to 30 knts but the sea flatter in the squalls. Practical experience has shown me that the conditions in similar speeds can be very different, but I had attributed this to the fetch, sea state etc, rather than the physical componenet of the wind as opposed to just it's speed. However I can now understand how the density of the wind and the surrounding atmosphere, can have an effect on the 'suck' and 'push' effect of the sails. Can where you are in relation to the depression also effect you differently for the same wind speed??
 
Jimi, you might like to read the page at http://www.bom.gov.au/weather/nsw/amfs/Wind%20Shear.shtml which gives a pretty good explanation as to how the apparant different "weight" in the wind comes about even though the wind speed is the same.

As another has said and I do too, the increased forces you may experience under some conditions at the same wind speed are not directly related to pressure or density - those things do not make enuff difference to be noticable on a yacht.

John
 
Interesting .. so basically the article is saying is that the wind speed is different at different heights and that difference in not always the same .. my wind instruments aare at masthead so its actually measuring the max wind speed experienced on my boat rather than the actual. Hmm ... would explain why boats with different mast heights read differently. Also in stable conditions mast head speed can be 3 times the deck speed whilst in unstable conditions its virtually the same.. in stable conditions that would make the average force on the sails appear proportionately higher to that experienced on the deck but conversely proportionately lower than that shown by mast head instruments .. lot of food for thought, good article John!
 
And also the direction of the wind can be different between deck and masthead also affecting heeling moment.

Regards

John
 
For what Its worth Pye_End has it.

When we talk about wind speed we are really talking about force. That’s how we measure it. From there on in its all self compensating therefore temperature / pressure / humidity –doesn’t matter because we understand the winds velocity through measuring its force against an object.
We talk of speed (Beaufort Scale etc.) but we actually mean force.

There is nothing to explain.

If we get instuments that actually measure wind speed by indicating how fast a molecule is moving on average in a direction (laser ?) then we may have some explianing to do.
 
so if I fling a ping pong ball and a steel ball bearing at you at equal velocity then they both hit you with equal force?
 
Err, No.

Cup anemometers mesure the wind speed directly. As the same fluid is acting on both cups the only things that matter are the fluid speed, the drag coefficients of the cups, and the distance of the cups from the axis of rotation. Proof here.
 
Surely these equations are telling you how fast the anemometer goes, not that the drag co-effs are equal on either side?

Not sure how the first equation is derived, but appreciate roughly where it is coming from.

Not sure if I fully understand what the 2nd and 3rd equation is telling us (are they different in some way?).

Also, you are assuming that the air density is the same for the coming towards you as the one going away from you - is this a fair assumption?

Please explain.
 
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