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Woodbotherer View Drop Down
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Posts: 192 		Post Options Post Options   Quote Woodbotherer Quote  Post ReplyReply Direct Link To This Post Topic: Old age or weather conditions
    Posted: 23 Feb 15 at 12:41pm
I've read and had that described to me before, it was an argument made on the windsurfing forum, one just has to assume that as it's on the way back down then it has reverted to the level above molecular which sees water actually below air at surface level pressure or whatever physics it is that suggests moist air is lighter. Warm moist air I can see, but cold moist air, sorry that comes back down, so what is the science of that description and at what temperature was it detected?

Edited by Woodbotherer - 23 Feb 15 at 12:42pm
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turnturtle View Drop Down
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Posts: 2538 		Post Options Post Options   Quote turnturtle Quote  Post ReplyReply Direct Link To This Post Posted: 23 Feb 15 at 1:16pm
Originally posted by transient

 
edit......not sure what happens if there is solid water (rain drops) in  the air though.

your rig gets wet, therefore it's heavier to handle?
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maxibuddah View Drop Down
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Posts: 1760 		Post Options Post Options   Quote maxibuddah Quote  Post ReplyReply Direct Link To This Post Posted: 23 Feb 15 at 1:44pm
That and your hands are cold and wet so don't work as well, appearing to make things feel heavier too
Everything I say is my opinion, honest
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alstorer View Drop Down
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Posts: 2899 		Post Options Post Options   Quote alstorer Quote  Post ReplyReply Direct Link To This Post Posted: 23 Feb 15 at 2:15pm
Ignoring rain for now (because I can't answer that) lets go basic science.

Very roughly, a given quantity of gas molecules will occupy a set volume, regardless of what those molecules are- the elements and compounds in air generally behave close to an idea gas, so at a pressure of 1 atmosphere (1000mB, 29.53 inches of mercury) 1 mole* of gas occupies 24.465 litres at 25°C- or 1 litre of air contains 0.04 moles of gas- approximately 80% of this is Nitrogen, with a molecular weight of 28, and 20% is Oxygen, with a molecular weight of 32. A water molecule has a molecular weight of 18. Up to 5% of local atmosphere can be water vapour.

What I'm not sure is how all this applies. regardless of gas composition or temperature, 1 Pascal of pressure is 1 newton of Force on 1 square metre of area.




*not small furry mammals. 6.02x10^23 atoms/molecules/other of a substance. A useful unit when doing chemistry.

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transient View Drop Down
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Posts: 715 		Post Options Post Options   Quote transient Quote  Post ReplyReply Direct Link To This Post Posted: 23 Feb 15 at 2:20pm
Originally posted by turnturtle


your rig gets wet, therefore it's heavier to handle?


the amount I capsize that's situation normal.

Molecular weight of water vapour is approx 18 g/mols
Molecular weight of dry air (average of it's components) is approx 29 g/mols


edit ....see above, Al posted same time as me, didn't see it.


Edited by transient - 23 Feb 15 at 2:24pm
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boatshed View Drop Down
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Posts: 457 		Post Options Post Options   Quote boatshed Quote  Post ReplyReply Direct Link To This Post Posted: 23 Feb 15 at 3:32pm
Originally posted by alstorer

6.02x10^23 atoms/molecules/other of a substance.



As the chemistry joke goes "I don't trust atoms, they make up everything"


Edited by boatshed - 23 Feb 15 at 3:33pm
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Strangler View Drop Down
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Posts: 154 		Post Options Post Options   Quote Strangler Quote  Post ReplyReply Direct Link To This Post Posted: 23 Feb 15 at 4:15pm
The excellent Frank Singleton website will answer your question-
http://weather.mailasail.com/Franks-Weather/Weight-Of-Wind
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Steve411 View Drop Down
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Posts: 705 		Post Options Post Options   Quote Steve411 Quote  Post ReplyReply Direct Link To This Post Posted: 23 Feb 15 at 4:15pm
Originally posted by boatshed

Originally posted by alstorer

6.02x10^23 atoms/molecules/other of a substance.



As the chemistry joke goes "I don't trust atoms, they make up everything"

That's quite a good joke for a chemist.
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sargesail View Drop Down
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Posts: 1459 		Post Options Post Options   Quote sargesail Quote  Post ReplyReply Direct Link To This Post Posted: 23 Feb 15 at 7:49pm
Steve,

As per my answer on the 300 site: you were cold (and old).
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fab100 View Drop Down
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Posts: 1005 		Post Options Post Options   Quote fab100 Quote  Post ReplyReply Direct Link To This Post Posted: 23 Feb 15 at 10:49pm
Here's a different whacky theory Mr B...

Inland, some days the breeze is quite 'clean', relatively stable in strength and direction. My guess is that most of the air flow here is horizontal. Other days, the wind feels all chopped up, just all over the place; burgees spin and tell you the opposite to the tell-tales, the boat won't settle into a stable groove. My interpretation (FWIW) is that there is a significant element of mixing of the layers, with down drafts, up drafts etc.

In the latter case, it's virtually impossible to get the rig working efficiently, perfect trim in one bit of the sail is totally wrong on another. As a consequence, you work harder and the rig fights back; harmony and equilibrium just ain't gonna happen.

I reckon this is what you faced. Further, I'd wager that if you spoke to someone trying to trim an asymmetric kite in the same race, they'd say it was noticeably even more of a bitch of a job than usual.

On these days, I've been on a run in my laser and had the lower quarter of the sail blow up and back as if the wind was blowing out of the water and up at 45degrees from in front of me.
, whilst the rest was happy I was indeed on a run.

In Clive's vocabulary of wind this is called a "what the ****". 
Great book for Club Sailors here
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