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Why does a gennaker/kite lift the bow?

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17mika View Drop Down
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Post Options Post Options   Quote 17mika Quote  Post ReplyReply Direct Link To This Post 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 LOL
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Post Options Post Options   Quote Lukepiewalker Quote  Post ReplyReply Direct Link To This Post 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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Post Options Post Options   Quote winging it Quote  Post ReplyReply Direct Link To This Post Posted: 12 Mar 12 at 6:01pm
oh god, I'm getting my coat....
the same, but different...

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Post Options Post Options   Quote 2547 Quote  Post ReplyReply Direct Link To This Post Posted: 12 Mar 12 at 6:01pm
Of course it lifts the bow ...
 
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JohnW View Drop Down
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Post Options Post Options   Quote JohnW Quote  Post ReplyReply Direct Link To This Post Posted: 12 Mar 12 at 6:04pm
All the photos of 12 foot skiffs prove it!!
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Post Options Post Options   Quote winging it Quote  Post ReplyReply Direct Link To This Post Posted: 12 Mar 12 at 6:22pm
nah, it's because they all stand at the end of the boat.... LOL
the same, but different...

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Post Options Post Options   Quote x1testpilot Quote  Post ReplyReply Direct Link To This Post 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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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post 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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Post Options Post Options   Quote RS400atC Quote  Post ReplyReply Direct Link To This Post 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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Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post 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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