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JimC View Drop Down
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    Posted: 28 Jan 16 at 9:45pm
Originally posted by Daniel Holman


Also, you wouldn't adjust it coming out of tacks as that would be such a tiny percentage of the total time sailing

Come sail a Canoe Dan, and you'll be amazed how much time you lose tacking! Still, I expect you're right. I can't imagine doing it myself.
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Posts: 997 		Post Options Post Options   Quote Daniel Holman Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan 16 at 9:41pm
Originally posted by realnutter

Originally posted by Daniel Holman

- the gybing daggers above gybe at all states of retraction.



Is a suitably shaped dagger board actually a good foil?..  It goes against all teaching to build a foil with max thickness toward the rear edge..


the daggerboard is shaped as one would optimally shape it, it then slides up and down through a diamond shaped "box" which then sits in the square case - should be evident in the pics above
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Posts: 129 		Post Options Post Options   Quote realnutter Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan 16 at 9:36pm
Originally posted by Daniel Holman

- the gybing daggers above gybe at all states of retraction.



Is a suitably shaped dagger board actually a good foil?..  It goes against all teaching to build a foil with max thickness toward the rear edge..


Edited by realnutter - 28 Jan 16 at 9:38pm
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Posts: 997 		Post Options Post Options   Quote Daniel Holman Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan 16 at 9:23pm
Originally posted by Do Different

So reading all that has been said by respected designers and theorists.

If I have understood correctly.

A gybing board does not have magical properties that make a board "climb" to windward and there is no such thing as something for nothing. The most significant benefit is to allow the boat to track straight through the water for most efficient use of hull shape.
Yes basically - you aren't inducing drag off the hull by dragging it sideways through the water by a few degrees (up to 10% extra drag!)
If the above is right, given that hull alignment is top effect can I ask a couple of simple minded questions.

Would a heavily chined hull shape benefit more than a round dish? Maybe - different hulls have different performances in yaw

Is the benefit greater in displacement mode, as when planing there is less hull in the water and what is would most likely be pretty flat anyway?
Generally greater benefit in disp mode as when pinching the same RM and SF is being derived froim the same area at lower speed, so bigger Cl needed so consequently bigger yaw angle, so more case for a gyber
Does the fact that gybing boards are big in Five Oh's (round and planing hulls) mean the above questions are total tosh or Five Oh's simply love tech? Big class peopled by wealthy motivated and clever gents. rules allow it. Culture of tweaking. Big gains in some conditions.







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Posts: 997 		Post Options Post Options   Quote Daniel Holman Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan 16 at 9:16pm
Originally posted by realnutter

As I understand it... gybing boards only work when fully down.. it's the bit that remains in the case that is shaped to allow the magic to happen...

Pull the plate up, as you would off the wind., and planing, and they can no longer gybe...

Thats the case for a gybing CB which has a diamond shaped head - the gybing daggers above gybe at all states of retraction.
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Posts: 129 		Post Options Post Options   Quote realnutter Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan 16 at 9:12pm
As I understand it... gybing boards only work when fully down.. it's the bit that remains in the case that is shaped to allow the magic to happen...

Pull the plate up, as you would off the wind., and planing, and they can no longer gybe...
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Posts: 1312 		Post Options Post Options   Quote Do Different Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan 16 at 9:08pm
So reading all that has been said by respected designers and theorists.

If I have understood correctly.

A gybing board does not have magical properties that make a board "climb" to windward and there is no such thing as something for nothing. The most significant benefit is to allow the boat to track straight through the water for most efficient use of hull shape.

If the above is right, given that hull alignment is top effect can I ask a couple of simple minded questions.

Would a heavily chined hull shape benefit more than a round dish?

Is the benefit greater in displacement mode, as when planing there is less hull in the water and what is would most likely be pretty flat anyway?

Does the fact that gybing boards are big in Five Oh's (round and planing hulls) mean the above questions are total tosh or Five Oh's simply love tech?
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Posts: 997 		Post Options Post Options   Quote Daniel Holman Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan 16 at 8:43pm
Originally posted by iGRF

You could 'spring' the diamond, so more pressure gives max angle and less pressure reduces it, but I'm not sure that's the way round you want it, then actually you could spring the other side for the opposite effect, wait a minute, this needs more dwelling on, so like a suspension ATB you springload with adjustable tension, I'm going to think further about this...
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Posts: 997 		Post Options Post Options   Quote Daniel Holman Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan 16 at 8:41pm
Originally posted by iGRF

You could 'spring' the diamond, so more pressure gives max angle and less pressure reduces it, but I'm not sure that's the way round you want it, then actually you could spring the other side for the opposite effect, wait a minute, this needs more dwelling on, so like a suspension ATB you springload with adjustable tension, I'm going to think further about this...
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Posts: 997 		Post Options Post Options   Quote Daniel Holman Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan 16 at 8:38pm
Originally posted by JimC

Originally posted by iGRF

It then follows that this angle should be adjustable, because that leeway angle must surely alter with wind strength on some hull forms,


I've not heard of it being done, but I agree, that would seem to be the logical approach. Indeed in an ideal world I suspect one would dial in a lot of angle coming out of a tack, and reduce it as the boat comes up to speed and the foil generates more lift.
The ultimate expression would presumably be a daggerboard in which the leading portion was a gybing foil with adjustable angle of incidence, and the trailing portion was a flap so the foil was adjustable with the total camber able to be altered... I think I know a Canoe sailor in California who would build that, if indeed he hasn't already!


Also, you wouldn't adjust it coming out of tacks as that would be such a tiny percentage of the total time sailing



Edited by Daniel Holman - 28 Jan 16 at 8:39pm
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