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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 Topic: Wiki Sail by GRF
    Posted: 18 Apr 13 at 10:37am
Love the proper science Transient and Al. Shows how much I've lost in the decades since my A levels.

But remember this is the GRF wiki, so the rules of physics and chemistry don't apply.

The point that strikes a chord with me is about how windspeed is usually measured - with a spinning cup device. As they are effectively tiny sails, the impact of any changes of temperature/pressure/humidity are surely the same on both - if the consequent 'feel' from the rig is different, those factors will be measured by the anemometer.

Few of us actually carry an anemometer, but I suspect we do use our general sense of touch to judge what the windspeed is - and those changed temperature/pressure/humidity factors could knock our experience-based calibration out of whack.
Great book for Club Sailors here
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L123456 View Drop Down
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Posts: 500 		Post Options Post Options   Quote L123456 Quote  Post ReplyReply Direct Link To This Post Posted: 18 Apr 13 at 10:41am
Originally posted by iGRF

I don't care what the google scientologists reel out here.

Air with moisture in it feels heavier than air without moisture in it

Cold Air feels heavier than warm air.

Cold Air with moisture in it feels heavier than Cold Air without moisture even more so if it is actually raining.

Warm Air with moisture in if feels heavier than warm air without moisture in it.

Facts, pure anecdotal facts derived from holding sails in ones bare hands in those circumstances.

Resulting in sail size choice accordingly. (Bigger sails in warm less moist air, smaller sails in cold.

What you lot feel may of course, like the way you speak, be different because it is conducted by and large through your arse..

Well you have observed the differences but rather than understand the physics you have once again invented your own branch of "physics" often referred to as bullsh*t or b**locks ...
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Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 18 Apr 13 at 10:46am
Originally posted by iGRF

...anecdotal facts...
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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: 18 Apr 13 at 10:53am
Originally posted by maxibuddah

There's some very clever people on here, or they know where to look on Google.  

LOLWe all learn from somewhere, google is as good a place to start as anywhere.


I looked into this a couple of years ago after a few speculative conversations at the club: Initially we concluded that high humidity gave extra oomph for a given wind speed....When bored I checked it out and was surprised to find the opposite was the case. Since then I have been keeping a mental note on those extra oomph days.
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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: 18 Apr 13 at 10:53am
Originally posted by maxibuddah

There's some very clever people on here, or they know where to look on Google. I know what jimbo means though, is about risk versus warmth.
No googling- I'm a proffesional chemist. I don't work with gasses (in fact, I work with epoxies) but that degree hasn't been entirely forgotten!
-_
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Posts: 715 		Post Options Post Options   Quote transient Quote  Post ReplyReply Direct Link To This Post Posted: 18 Apr 13 at 11:01am
Originally posted by fab100

Love the proper science Transient and Al. Shows how much I've lost in the decades since my A levels.

But remember this is the GRF wiki, so the rules of physics and chemistry don't apply.

The point that strikes a chord with me is about how windspeed is usually measured - with a spinning cup device. As they are effectively tiny sails, the impact of any changes of temperature/pressure/humidity are surely the same on both - if the consequent 'feel' from the rig is different, those factors will be measured by the anemometer.

Few of us actually carry an anemometer, but I suspect we do use our general sense of touch to judge what the windspeed is - and those changed temperature/pressure/humidity factors could knock our experience-based calibration out of whack.

Speed and power (or weight) of gases are different things.

Heavy wind or light wind effects power not speed. A wind speed indicator will measure 20 knots reasonably accurately in water as well as wind (provided the bearings aren't knackered).....The weight of the gas will effect deceleration and acceleration of the cups not the eventual speed. The friction in the bearings will have some effect but not much that you'd notice unless in a drifter.


Edited by transient - 18 Apr 13 at 11:04am
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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: 18 Apr 13 at 11:10am
Originally posted by transient

Speed and power (or weight) of gases are different things.

Heavy wind or light wind effects power not speed. A wind speed indicator will measure 20 knots reasonably accurately in water as well as wind (provided the bearings aren't knackered).....The weight of the gas will effect deceleration and acceleration of the cups not the eventual speed. The friction in the bearings will have some effect but not much that you'd notice unless in a drifter.

Interesting, thanks.

So how does that speed/power translate from anemometer acceleration and rotation rate to the output from our sails please?

We are in danger of reaching a proper solution here - perhaps a first!
Great book for Club Sailors here
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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: 18 Apr 13 at 11:19am
I'll admit to getting out of my depth here, perhaps someone better qualified will explain.

Here's my 2 cents though:

The speed/power thing on a wind indicator holds true because of minimal friction or drag of the bearings........a boat however has masses of drag.....Dense air although not faster (the wind that is) will accelerate the boat quicker and overcome more drag so the boat will go faster...... perhaps more importantly  the gusts will feel harder.



edit:
 Although I claim to notice the difference, many don't and argue it's not significant (see last para in link):




Edited by transient - 18 Apr 13 at 11:43am
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RS400atC View Drop Down
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Posts: 3011 		Post Options Post Options   Quote RS400atC Quote  Post ReplyReply Direct Link To This Post Posted: 18 Apr 13 at 11:55am
FWIW there are plenty of ultrasonic wind-ometers out there.
Also ones that work by the air cooiling a hot wire.
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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: 18 Apr 13 at 12:02pm
Well done on managing to remember such things al. If only I really knew what you lot were on about and I had more time to digest it and learn..... I'll stay uneducated for now me thinks. Keep up the good work though I may pick it up by accident
Everything I say is my opinion, honest
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