Beafort and gusts

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tmh900

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Just glanced at Chimet. "Mean speed = 16Kn (F4)". "Highest gust = 17.6Kn (F5)".

I know this has been discussed before and the general conclusion is you can't have Fx gusting Fy. It is either Fx OR Fy. So in the Chimet example, F4 has a % alowance over 16 Kn built in for gusts - so it is basically deffo a F4 not an F5.

I know informally, many folks write '...it was F7 gusting F8...', but is seems even some of the 'official' sites now break the convention.

Is it time to lobby the authorities, or just go with the flow?
 
As I understand it, the Beaufort scale was originally devised to describe seastate when well offshore. So it should really be related to the average windspeed over some hours.

Dinghy sailors need for information than that, we want to know gust strength. The Beaufort wind numbers are useful for this, as you can never measure wind exactly and Beaufort scale is a good level of resolution.

I'm very happy that Chimet tells me whether it's F4 gusting F5 or F4 gusting F7, it's useful to know, and much quicker than analysing the raw numbers.

If you look at Hurst wind data instead, there is a lot more info there, including useful stuff on backing and veering, but it's a lot to take in, compared to a useful measure of the base wind level and the gust level.
 
lw395 said:
As I understand it, the Beaufort scale was originally devised to describe seastate when well offshore. So it should really be related to the average windspeed over some hours.

Dinghy sailors need for information than that, we want to know gust strength. The Beaufort wind numbers are useful for this, as you can never measure wind exactly and Beaufort scale is a good level of resolution.

I'm very happy that Chimet tells me whether it's F4 gusting F5 or F4 gusting F7, it's useful to know, and much quicker than analysing the raw numbers.

If you look at Hurst wind data instead, there is a lot more info there, including useful stuff on backing and veering, but it's a lot to take in, compared to a useful measure of the base wind level and the gust level.
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With both your examples, the sea state will be basically as per F4?
 
tmh900 said:
Just glanced at Chimet. "Mean speed = 16Kn (F4)". "Highest gust = 17.6Kn (F5)".

Is it time to lobby the authorities, or just go with the flow?
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I think it quite useful to know if you are getting a steady windspeed, or a gusty one, especially when sailing with number 2 daughter.
 
Call me a heretic if you will, but I hate the beaufort scale. IMHO is should be binned. I am much happier with knots, mph or even metres per second.

Give me " 15 knots, gusting 40" anytime.

It seems madness to have one system for only sailing. Pilots, walkers, landlubbers etc all survive without beaufort. It's not like we are signalling in morse any more!
 
Pye_End said:
I think it quite useful to know if you are getting a steady windspeed, or a gusty one, especially when sailing with number 2 daughter.
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I'm fine with two numbers in knots, one for mean and one for gusts (agree the latter can make a difference to the sailing pleasure). Mine was more a point of pedantry - that the gusts can't technically have an 'F' number.
 
snooks said:
Heretic! Burn HIM! :D
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Quite!

To continue the rant, I guess this is another of those empire things we can't do without. Where I learnt to sail, everything was in metres per second, kilometres and millibars. Then I learnt to fly and that had knots and feet. Then I bought a russian plane and that had hectopascals, metres and kph, and now I sail in England I have to learn forces and miles.

How many euros is that anyway!
 
tmh900 said:
I'm fine with two numbers in knots, one for mean and one for gusts (agree the latter can make a difference to the sailing pleasure). Mine was more a point of pedantry - that the gusts can't technically have an 'F' number.
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Perhaps it should move a little with the times and what it's being used for. On a square rigger, a 30 second gust of 30kts will not have much influence, compared to a long periond of 30 knots.
Whereas on a dinghy or small yacht, it will blow you over.
Chimet is there for practical purposes, if you want to be pedantic it's wrong anyway, because the anemometer isn't 10m above sea level...

Best not to knock something useful that's free!
 
lw395 said:
...
Chimet is there for practical purposes, if you want to be pedantic it's wrong anyway, because the anemometer isn't 10m above sea level...

Best not to knock something useful that's free!
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I'm not knocking Chimet - agree its still a vaulable resource. It just appears that increasingly the convention is being disregarded. You have informal reports (e.g. posts on here), slightly more formal e.g. Chimet, and I'm sure I have seen some publications from organisations that really should know better refer to 'gusting Fx' (can't recall where, but could have been met office or MCA :eek:).

I can't say that it bugs me, but as a relative newcomer, why did I bother learning the theory if no one uses it?

Maybe its time the convention was changed?
 
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tmh900 said:
I know informally, many folks write '...it was F7 gusting F8...', but is seems even some of the 'official' sites now break the convention.
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... Even some of the YM reporters are taken in by this.

Chris Beeson wrote in his boat test of the Elan 310 (Dec 09 edition):

Bramble weather beacon .... was showing a 20-knot average and gusts of 28 ...... how wise would it be to test a twitchy-looking 31 ft yacht in a near gale?
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Nooooooooooo! 20 knots is force 5 (Fresh wind). Ignore the gusts, because they are factored into the average, along with the lulls. A near gale needs an AVERAGE wind speed of around 30 knots.
 
Angele said:
... Even some of the YM reporters are taken in by this.

Chris Beeson wrote in his boat test of the Elan 310 (Dec 09 edition):



Nooooooooooo! 20 knots is force 5 (Fresh wind). Ignore the gusts, because they are factored into the average, along with the lulls. A near gale needs an AVERAGE wind speed of around 30 knots.
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My point exactly! Why bother with forces, near gales and whatever. We all know what 20 knots is. Leave it at that.
 
tmh900 said:
I can't say that it bugs me, but as a relative newcomer, why did I bother learning the theory if no one uses it?

Maybe its time the convention was changed?
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Where is this supposed convention laid down? The Met Office definitions make no reference to average values. How would you do the average, anyway, since the scale is non-linear.
 
Ubergeekian said:
Where is this supposed convention laid down? The Met Office definitions make no reference to average values. How would you do the average, anyway, since the scale is non-linear.
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UberG

Sorry to disagree with you old chap, but yes they do! See the word "mean" in the top row.;)

Conveniently, this answers your question as to how they do it - arithmetic mean, as distinct from any of the other averages (e.g. median or mode).

Remember those lessons on statistics?:p
 
Ubergeekian said:
Where is this supposed convention laid down? The Met Office definitions make no reference to average values. How would you do the average, anyway, since the scale is non-linear.
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I still can't locate the definitive source, but here are some snippets from "RYA Weather Handbook"

"Wind speed and direction in a forecast refer to an average wind speed over a 5 or 10 minute period.... On an average day, if there is such a thing, we can expect gusts to be as third as much again as the forecast".

goes on to say:

"...forecast...gale warnings issued if the winds are expected to exceed Force 8 (or if gusts are expected to reach Force 9)"
 
Angele said:
UberG

Sorry to disagree with you old chap, but yes they do! See the word "mean" in the top row.;)

Conveniently, this answers your question as to how they do it - arithmetic mean, as distinct from any of the other averages (e.g. median or mode).

Remember those lessons on statistics?:p
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...actually, I admit I'm being a little unfair on UberG. The use of "mean" in the Met Office definition table is at best unclear as to whether it is referring to an average wind strength or the average of the top and bottom of the range that goes with a particular Beaufort strength.

Sorry UberG.:o
 
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