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Why does a gennaker/kite lift the bow? |
Post Reply | Page 123 4> |
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17mika
Groupie Joined: 03 Nov 06 Location: Italy Online Status: Offline Posts: 53 |
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Topic: Why does a gennaker/kite lift the bow? Posted: 12 Mar 12 at 5:49pm |
As simple as the subject above; but still I cannot get the answer. Anyone can help? I mean, I know (or at least I think I know) that a kite is a highly tapered and swept wing, with more and more taper as you go upwards to the head of the sail. But then, again, what does it has to do with upward lift?
Thanks in advance for the answers; I know that once I get it, I'll be at least a couple of knots faster around the course
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Lukepiewalker
Really should get out more Joined: 24 May 06 Location: United Kingdom Online Status: Offline Posts: 1340 |
Post Options Quote Reply Posted: 12 Mar 12 at 5:56pm |
Run away! Run away! Before JimC gets here...
Or, to put it another way, it doesn't. |
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Ex-Finn GBR533 "Pie Hard"
Ex-National 12 3253 "Seawitch" Ex-National 12 2961 "Curved Air" Ex-Mirror 59096 "Voodoo Chile" |
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winging it
Really should get out more Joined: 22 Mar 07 Online Status: Offline Posts: 3958 |
Post Options Quote Reply Posted: 12 Mar 12 at 6:01pm |
oh god, I'm getting my coat....
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the same, but different...
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2547
Really should get out more Joined: 11 Aug 11 Online Status: Offline Posts: 1151 |
Post Options Quote Reply Posted: 12 Mar 12 at 6:01pm |
Of course it lifts the bow ...
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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: 12 Mar 12 at 6:04pm |
All the photos of 12 foot skiffs prove it!!
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winging it
Really should get out more Joined: 22 Mar 07 Online Status: Offline Posts: 3958 |
Post Options Quote Reply Posted: 12 Mar 12 at 6:22pm |
nah, it's because they all stand at the end of the boat....
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the same, but different...
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x1testpilot
Posting king Joined: 11 Feb 11 Location: Ealing Online Status: Offline Posts: 175 |
Post Options Quote Reply Posted: 12 Mar 12 at 6:34pm |
It's the angle of the sail to the boat/wind/water. The force on the sail is perpendicular to the sail. think of a wooden board held in the wind, if you hold it to the top (leading edge) is into the wind and the bottom at 45 degrees to the leading, you will feel lift (also a real kite).
The leverage of a long spin pole will make the effect more pronounced. Having said that the effect can't be that significant as 14's skiffs etc do tend to stand at the back of the boat + the wind is pushing the main forward too. I expect a better explanation will be forthcoming! |
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JimC
Really should get out more Joined: 17 May 04 Location: United Kingdom Online Status: Offline Posts: 6649 |
Post Options Quote Reply Posted: 12 Mar 12 at 6:57pm |
It doesn't.
There may be a lifting effect on the boat as a whole, but the bow is always pushed down. http://www.devboats.co.uk/cherubweb/liftbow.htm If it did you would see trapeze crews going for the front of the boat to get the weight forward when a gust hits. Edited by JimC - 12 Mar 12 at 6:58pm |
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RS400atC
Really should get out more Joined: 04 Dec 08 Online Status: Offline Posts: 3011 |
Post Options Quote Reply Posted: 12 Mar 12 at 7:12pm |
I think Jim's argument is a little spurious, because in most of the bow up pictures, the crew are back but the upward force of the water is also concentrated aft.
The sum of the vectors of the 3 strings on a kite pulls in a certain line. Whether that is pulling the bow up or down depends also on where the reaction force (drag on the hull etc) is ahead or astern of that line. |
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Rupert
Really should get out more Joined: 11 Aug 04 Location: Whitefriars sc Online Status: Offline Posts: 8956 |
Post Options Quote Reply Posted: 12 Mar 12 at 7:15pm |
There are many tales of boats going down the mine less once the kite is up, but this doesn't mean it gives lift. What does happen is beyond me, though - probebly to do with centres of effort or something.
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