I know this is probably in the worng place and it should be in weather but im not sure how mnay poeple go there.

Ok... if you have an anamometer that reads 20knots in the UK (Cold damp air MORE DENSE AIR) and a anamometer that reads 20 knots in Dubai (hot dry LESS DENSE AIR)

Are they both produceing 20knots?

If yes then is the force they are blowing the same as the denser air must provide more particles as there is more of them fitting your sail?

Kind of confused on this

i had to go and get a drink i didnt want to be harsh thnkyou so much isis

now

I know this is probably in the worng place and it should be in weather but im not sure how mnay poeple go there.

Ok... if you have an anamometer that reads 20knots in the UK (Cold damp air MORE DENSE AIR) and a anamometer that reads 20 knots in Dubai (hot dry LESS DENSE AIR)

Are they both produceing 20knots?

If yes then is the force they are blowing the same as the denser air must provide more particles as there is more of them fitting your sail?

Kind of confused on this

One  example i have heard is that an aeroplane that takes off in dubai mid summer must have a higher take off speed to get the lift than it must in the uk where the air is denser.

So for colder denser wind do we get more power per knot of wind than in a hot country with lower density.

thanks for that it has cleared some of it up.

So an anamometer built in the uk set to measure wind on a summers day at sea level in the uk is not accurate anywear else.

And yes i agree the beaufort is what on what you can see not a measurement.

I read Ian99 as saying that a decent anemometer will measure speed not force. As such, it would be equally accurate anywhere.

Of course, it depends on how you define 'decent'. I'd have thought that a good rotating turbine-style of anemometer would have such minimal bearing drag that the turbine would always effectively spin at a rate proportional to the windspeed, regardless of the air density, i.e. it will be accurate everywhere.

An instrument that depends on the pressure force exerted by the fluid - e.g. a vane with a pointer that moves against a spring or gravity, will depend on density and therefore be less accurate. That said, anybody who's used an anemometer will know that the fluctuations are usually so great, gust to lull, that such inaccuracy would be hardly noticeable and thus irrelevant, or so I'd have thought...

no offence really to Julian beithewaite because he has designed some of the best boats in the world, but from past experiance i do not think you would think hes god if you met him.

At the 29er Worlds in 2005 julian made up a rule that we had to measure the spreader hieght that wasnt in the rules, and he also said that you weigh a 29er with the pole in which is not correct (but julian said so, so it was done). There was hardly any boats underweight and most were 1.5kg over which is about the weight of the pole.

back to the topic, i agree that when it is warmer the wind is not as powerful for its speed as a cold UK winter breeze.

And all your tuning efforts are worthless when you go arse over tit in a gybe and end up swimming or have to spin after hitting the mark.

My veiw spend more time on your boat handling skills than worrying about which country you well get most wind.

 I second that!

(she says after flunking a tack yesterday and ending in the drink...)

we did it on a gybe a few weeks back. about 18 to 20 knots

ready to gybe chris

yep

ok nice and easy

go

me face down on the mast chris landing on my back

all in the space of 2 seconds from our last words what happened

im going to be technical here because im just about sure i understand this:

the speed of the wind measured by an anemometre with paddles or windmill type things will always be constant, no matter the pressure. all that matters is the difference between the friction on the front of the blade to the friction on the back. if there are more particles hitting the front and speeding it up, there must be more particles hitting the back and slowing it down. therefore the speed measured will be constant.

After having sailed in silvaplana for 2 weeks we definatly noticed that the wind speed did not relate to what we were use to back in Britain. To give you an idea the anemometer was reading 25knots average but when we were sailing it felt about 18-20 knots whilst sailing. Thats why the british are good in heavy winds compared to the rest of the world and generally not as fast in the lighter stuff... lol

water in the air would have a bigger effect than temperature id have thought.

Cold damp air = heavy = more rate of change of momentum [Kgm/s/s] per chunk of air slowed down by your sails = more force [N = Kgm/s/s]

Hot dry air = light = less force per wind speed.

What your wind gauge reads is the actual velocity of the air particles because (if well designed) it doesn't resist the wind and needs almost no force to keep it spinning.  Ie it's a velocity meter not a force meter.

So yes force 4 on a cold wet winter's day is windier than force 4 in a desert.  Ie the wind speed's the same but you get more push per knot!

My boats certainly go faster per wind knot in winter.  Doesn't everyone's?

There's a lot of truth in that, Rupert.

I'd just like to throw in the thought that water vapour weighs less per unit volume than oxygen or nitrogen. Question is, does it displace oxygen and ntirogen and reduce the density of air, or does it co-exist and add to it? I used to know... Something about Avogadro's hypothesis isn't it?