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Debunking Dodgy Sailing Theories |
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G.R.F.
Really should get out more Joined: 10 Aug 08 Location: United Kingdom Online Status: Offline Posts: 4028 |
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Topic: Debunking Dodgy Sailing Theories Posted: 20 Oct 11 at 10:27pm |
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Well without getting over complicated both work in the same way, the flow over the surface needs to be exhausted, so it is the same as the propellor blade in water, the sail in air, both fluid flow over a foil generating a force propelling a boat forward. Sails generally were slow acting foils, as speeds have increased, apparent wind increases, foils have twisted more and become higher in aspect ratio. For a while windsurfing drove that increase in twist, but it has passed on to high aspect cat foils and even fixed wings have to have twist in order to function. Old school dinghy sails had some twist but they were pin heads, so getting 'twist' used to be a complicated affair. With the advent of higher aspect (fatter headed) sails the twist is easier to dial in. But twist is there for more than just the perceived variation of wind speed at different heights, that's another old wives tale. The primary reason is to increase the speed of the flow by exhausting without turbulence at the leech or tip vortices (like you try not to get with glider wings).
Edited by G.R.F. - 20 Oct 11 at 10:28pm |
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RS400atC
Really should get out more Joined: 04 Dec 08 Online Status: Offline Posts: 3011 |
Post Options Quote Reply Posted: 21 Oct 11 at 8:19am | |
Only in your world! In the real world, we can measure the different windspeed (and direction) as a function of height. Its significance can vary, but sometimes you want a lot of twist for this reason. Or were you taking the view that old wives sometimes knew a thing or two? |
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2547
Really should get out more Joined: 11 Aug 11 Online Status: Offline Posts: 1151 |
Post Options Quote Reply Posted: 21 Oct 11 at 9:22am | |
yeah ... after no doubt millions spend researching the matter look how heavily twisted they are running ... |
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rogue
Really should get out more Joined: 04 Dec 08 Location: United Kingdom Online Status: Offline Posts: 978 |
Post Options Quote Reply Posted: 21 Oct 11 at 9:47am | |
Seamonkey- it's a cat, it doesn't count, cats are not tactical, they are in GRF's words, "gehey"
of course, if you close the bow up and form the hull from one piece of plastic, then you get a tunnel-hulled scow... these of course are really cool. Edited by rogue - 21 Oct 11 at 9:48am |
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JohnW
Really should get out more Joined: 17 Jul 07 Location: United Kingdom Online Status: Offline Posts: 552 |
Post Options Quote Reply Posted: 21 Oct 11 at 10:39am | |
I think if you do the vector maths, the twist required would be less when you have a large apparent wind component which is probably why cats such as the ACs dont appear to need much twist in their wings. (EDIT: Im not a cat sailor, nor have I sailed with a wing sail - just considering the mathematical point of view which as we all know is often not as simple as we think).
Edited by JohnW - 21 Oct 11 at 10:42am |
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fudheid
Far too distracted from work Joined: 21 Apr 11 Location: 51.53 N 01.28 E Online Status: Offline Posts: 241 |
Post Options Quote Reply Posted: 21 Oct 11 at 10:41am | |
this is an all time favourite of old dudes on 4ksbs
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JohnW
Really should get out more Joined: 17 Jul 07 Location: United Kingdom Online Status: Offline Posts: 552 |
Post Options Quote Reply Posted: 21 Oct 11 at 10:51am | |
How about this old chestnut:
"the fastest way to round the leeward mark is 'wide in tight out' " |
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fudheid
Far too distracted from work Joined: 21 Apr 11 Location: 51.53 N 01.28 E Online Status: Offline Posts: 241 |
Post Options Quote Reply Posted: 21 Oct 11 at 11:03am | |
not the fastest but the best way, inside track upwind.....
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2547
Really should get out more Joined: 11 Aug 11 Online Status: Offline Posts: 1151 |
Post Options Quote Reply Posted: 21 Oct 11 at 11:08am | |
Ah ... that would be a great idea ... then it would slap up & down on the chop to slow you down whilst the cats go creaming past ... |
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I luv Wight
Really should get out more Joined: 28 Jan 05 Location: United Kingdom Online Status: Offline Posts: 628 |
Post Options Quote Reply Posted: 21 Oct 11 at 11:23am | |
What is planing? and how do you define it?
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