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Gybing Centreboards

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Mike Holt View Drop Down
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    Posted: 06 Oct 17 at 3:19pm
Originally posted by craiggo

Mike, clearly you've made it work for you in the 5 'o', but I'm interested to know if there are either conditions, or boats where you don't think it works?

That is a great question and I had to have a good think about it. So, where and how it works in my boat and where it doesn't. First off a description, we use a Waterat made High Aspect gybing foil, I believe 1.5 degrees of gybe. It always gybes unless we use a gybe stop, a simple "V" that is inserted over the beak of the board to stop the gybe. We use this very rarely.

Where its value is marginal is when it is windy and lumpy and flow is not consistent, then it feels a little draggy. Any other time I think that we are getting value. However the control we have over the rig in a 5O5 means that we are sailing with very close to optimal power from 8 knots to 20 knots of breeze. Above that it probably has no value.

So, my guess would be that boats that are quickly over powered, such as iGRF says of boards would have a limited time it adds value. 

Hope that makes sense.
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Post Options Post Options   Quote craiggo Quote  Post ReplyReply Direct Link To This Post Posted: 05 Oct 17 at 10:22pm
Mike, clearly you've made it work for you in the 5 'o', but I'm interested to know if there are either conditions, or boats where you don't think it works?
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Post Options Post Options   Quote Mike Holt Quote  Post ReplyReply Direct Link To This Post Posted: 05 Oct 17 at 7:12pm
There is no question that in a dinghy, used and installed correctly they work.
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Post Options Post Options   Quote Chris 249 Quote  Post ReplyReply Direct Link To This Post Posted: 05 Oct 17 at 5:07am
Originally posted by Dougaldog

All,

This is nearly associated with 'that' other thread running elsewhere on the forum - but isn't quite.

So...gybing centreboards. How far back to they go and when did they first come into practical use (as against just the theory behind their operation)

D
A sketch and theory was propounded by Curry in 1928

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Post Options Post Options   Quote Chris 249 Quote  Post ReplyReply Direct Link To This Post Posted: 05 Oct 17 at 5:05am
Originally posted by Dougaldog

All,

This is nearly associated with 'that' other thread running elsewhere on the forum - but isn't quite.

So...gybing centreboards. How far back to they go and when did they first come into practical use (as against just the theory behind their operation)

D
The theory was expounded in 1928 by Manfred Curry.


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The history and design of the racing dinghy.
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 17 at 10:16pm
It's one of those things that seems like a 'no brainer' when you first encounter it..... Seems like it is not quite so simple.
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Post Options Post Options   Quote drifter Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 17 at 8:35pm
Interesting topic. I sailed in a Goodwin  Hornet in the 70's which had a gybing board. Always wondered why, but lovely boat anyway
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Post Options Post Options   Quote Wiclif Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 17 at 7:57pm
To reply to Dougal's first post, the guy I first started work with, a chap called Billy Morton, made a gybing board for his 505.

He had stopped sailing 505's by the time I started work in 1970, so some time before that
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 17 at 5:38pm
The thing it did for the sailboard was to point high without the normal effort you had to do on a board to outpoint the mean. (Body angle, rig over sheeted hard across the centerline and beyond) the problem came when in order to engage the 'knock' that turned it off, (a block at the top rear of the foil) you had to rake it aft, this then depowered the foil by obviously altering the profile it presented and the board wouldn't point that comfortably at all, so it became all or bugger all, it also could develop a nasty 'rattle' on a dead run or deep reach.

I didn't just bin it out of hand, at the time I was working with Parkers who were in those days the go to 5 oh supplier and we were shipping hundreds of these boards I'd designed, so it was worth working on and we had a couple of goes, Milanese foils, so not cheap and a potential break through like this would have been worth thousands, but sadly it wasn't to be, even heavier riders couldn't make it go above the top end of a three early four, it also co-incided with the other break through we'd built in which was the fully retracting CB which was helping sales anyway, so two things to cope with was felt to be one too many.
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Post Options Post Options   Quote MikeBz Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 17 at 4:00pm
Originally posted by mozzy

Gybing dagger boards change the aspect of the hull and rig to the wind. The foils still travel through water at the same leeway.

Or to put it another way - the boat's heading (where the bow is pointing, or what your compass reads) changes but its course (the bearing of the groove you carve through the water) doesn't.  Except that... IF changing the angle that the hull drags through the water does yield an efficiency gain then you will travel a bit faster - the marginal speed increase will generate more lift in the hull/foil combo and hence reduce the leeway marginally (thus improving your course over the ground marginally), and you could of course trade that marginal speed increase for a bit of extra height and hence improve your course over the ground a tiny bit more.

If you overdo the gybe angle of the board then you will drag the hull through the water the 'wrong' way (bow to leeward of direction of travel, stern to windward of direction of travel) - it's hard to see how that would be anything but bad.

In the early 1970s Malcolm Goodwin built a Hornet with a gybing board (1782, Revolution) which absolutely cleaned up for many many years.  However he also greatly optimised the shape, so how much of its pace was down to the gybing board is debatable - faulty intuition lead many to believe that the gybing board made the boat 'move up to weather'.
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