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Assy kites lift the bow ....

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tgruitt View Drop Down
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Post Options Post Options   Quote tgruitt Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct 15 at 6:14pm
Originally posted by 2547

Originally posted by tgruitt

I hope you're not being serious?

Looks pretty bow up to me ...


That's because a lead mine has hit a wave!
Needs to sail more...
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Oinks View Drop Down
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Post Options Post Options   Quote Oinks Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct 15 at 6:44pm
The bowsprit on my boat always bends upwards in breezier weather. If that's not lift, what is it?
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Peaky View Drop Down
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Post Options Post Options   Quote Peaky Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct 15 at 7:48pm
^^^^Luff tension

What matters is not whether there is a force upwards but whether the moment from the sail is bow down or niw up moment. To figure that out draw an arrow from the centre of effort of the sail in the direction you think the force is acting (forwards and a bit upwards). Now extend that arrow backwards (and downwards) until it hits the water. If that line crosses the water in front of the centre of flotation of the hull then the sail is lifting the bow. If it passes behind it is depressing the bow. Either is possible, it just depends on the boat and sail geometry.
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Post Options Post Options   Quote Oinks Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct 15 at 8:12pm
Hmmm..not sure I get all that. Luff tension? Well the luff from the end of the bowsprit to the mast sheave is curved. I don't think that tension in the luff is causing the bowsprit to bend. However, one thing I know that does work, is in the F3-4 range we positively aim to keep weight just forward enough so that the bow doesn't lift more than the stem just clearing the water ie counteracting the bow wanting to lift. Now that defo works in practice. Theory..well...I'm confused!
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Peaky View Drop Down
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Post Options Post Options   Quote Peaky Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct 15 at 8:25pm
Not static luff tension like a jib, but yes the only thing bending the pole is tension in the tack line.

I can't post pictures from an iPad (unless someone knows how?), but it is a simple moment calc, like a see saw. Of course, flying a kite also makes the boat go faster which may give it a bow wave to climb. But that isn't the kite lifting the bow directly.
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I luv Wight View Drop Down
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Post Options Post Options   Quote I luv Wight Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct 15 at 8:27pm
When we were trying asymmetric kites in Cherubs a few years ago, masthead rigs vs 2/3 hoist, long bowsprits vs short ones - we found that the masthead kite - short pole was faster, but the low hoist- long pole was safer. ( and with no kite was much safer, albeit a bit slow )

http://www.bloodaxeboats.co.uk
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Jack Sparrow View Drop Down
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Post Options Post Options   Quote Jack Sparrow Quote  Post ReplyReply Direct Link To This Post Posted: 07 Oct 15 at 10:38am
Originally posted by ( and with no kite was much safer, albeit a bit slow )
[/QUOTE



Really? In your P6? 2 sail reaching was dea

Really? In your P6? 2 sail reaching was death in most Cherubs, and I don't remember your designs being the most easily sailed of the fleet!
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kneewrecker View Drop Down
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Post Options Post Options   Quote kneewrecker Quote  Post ReplyReply Direct Link To This Post Posted: 07 Oct 15 at 10:59am
the Emperor says that's not bow lift from a kite, this is bow lift from his new kite....




Edited by kneewrecker - 07 Oct 15 at 11:00am
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andymck View Drop Down
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Post Options Post Options   Quote andymck Quote  Post ReplyReply Direct Link To This Post Posted: 07 Oct 15 at 12:14pm
I have seen 2 x Rays that show the propensity of a L5k to pitch pole when 2 sail reaching. It never did it with the kite up. I am not totally convinced this is due to the alleged bow lift, but more boat balance and wind and wave angle. I suspect the culprit is often the mainsail which is often further out with more vang tension when the kite is down. This powers up the top of the mast causing more of a pitching moment.
We learnt on the 5k that playing the kicker was safer and more effective than the main sheet. Shame it took a fracture of my lumber spine to make us listen to the class stalwarts. The second x Ray belonged to another orthopaedic surgeon who did the identicle injury and mechanism.
Andy Mck
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