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Gybing Plates

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JimC View Drop Down
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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Topic: Gybing Plates
    Posted: 26 Jan 16 at 9:44pm
Originally posted by iGRF

That guy if you'll pardon my impatience is talking bollox.

I think he's more wrong than right though. It is striking that all the classes I know of where they seem to have gained a significant measure of popularity are two sail classes. I see two possible factors. They're all about the fact that what gybing boards do is in effect rotate the hull round the foil.

So the first effect is that if you get the gybe angle right then the hull centreline is aligned with the direction of travel, not crabbing by two degrees or whatever. I used to think that was probably insignificant, but I've seen some calculations by someone I respect which suggests it isn't.

The second effect is that the alignment of jib and mast changes (if you have a jib). The 505 guy goes into great flights of enthusiasm, in which I think he's forgotten that sailors sheet their sails relative to the apparent wind, not the hull, but nevertheless there is a change in an area where I find tiny changes matter.

As for the weight thing, well, yes, if your gybing board arrangement means you have a fatter case than someone without one, then that is a little more weight. Not convinced about the significance though.

Edited by JimC - 27 Jan 16 at 11:36am
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Post Options Post Options   Quote maxibuddah Quote  Post ReplyReply Direct Link To This Post Posted: 26 Jan 16 at 7:41pm
Draftsight is a free 2D CAD program that runs on windows, Linux and Mac. The link to the download pageis http://www.3ds.com/products-services/draftsight-cad-software/free-download/ Its from the same people who make Catia and Solidworks and is a pretty straight copy of autocad. Only does 2D stuff though
Everything I say is my opinion, honest
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 26 Jan 16 at 7:31pm
Yep even we used to try that in light weather with a foam block but it really doesn't make much difference unless of course your flushing strips are not cutting it as they should, which at championship level you really couldn't afford to happen, back in the day some of us would have a fresh set every major event.

The key thing about water in the centreboard case, isn't wether it's there or not, it's how badly it's moving about.

Edited by iGRF - 26 Jan 16 at 7:38pm
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Post Options Post Options   Quote RS400atC Quote  Post ReplyReply Direct Link To This Post Posted: 26 Jan 16 at 7:22pm
Originally posted by iGRF

That guy if you'll pardon my impatience is talking bollox. So much crap in what he was saying then, typical example of a good sailor having an opinion, juxtapositioning facts to support it and I can't be asked to pull it all apart, but he's wrong.

Carrying 2 kgs of water around in the centreboard case, yeah right... Whatever water is there, is there regardless and any more or less is a result of the efficiency or inefficiency of flushing strips, now attention does have to be paid to them if you are going to use gybing plates, but it's not beyond the wit of man to overcome.


Some people stuff the centrebox, instead of relying on slot gaskets.
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 26 Jan 16 at 6:24pm
That guy if you'll pardon my impatience is talking bollox. So much crap in what he was saying then, typical example of a good sailor having an opinion, juxtapositioning facts to support it and I can't be asked to pull it all apart, but he's wrong. Allthough I'm grateful nonetheless for you posting me a link I will have to come back to it later some of those equations annoyed me..

Carrying 2 kgs of water around in the centreboard case, yeah right... Whatever water is there, is there regardless and any more or less is a result of the efficiency or inefficiency of flushing strips, now attention does have to be paid to them if you are going to use gybing plates, but it's not beyond the wit of man to overcome.

Edited by iGRF - 26 Jan 16 at 7:54pm
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Post Options Post Options   Quote GarethT Quote  Post ReplyReply Direct Link To This Post Posted: 26 Jan 16 at 5:57pm
I vaguely recollect an article by a top OK sailor in the eighties where he said that any benefit from gybing a board had to be offset by the weight of the extra water you carried round in the centreboard case.


Edit: found it http://www.okdia.org/boat/manual/tm2_work.php

Edited by GarethT - 26 Jan 16 at 6:07pm
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iGRF View Drop Down
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 26 Jan 16 at 4:59pm
Originally posted by gordon1277

Hi GRF
Have a look at a free download called Trueview which allows you to view and plot CAD files.
Gordon
What a shame about all the boats lost at Cowes some peoples years of effort in restoration just gone plus classics we will never see again.
Awful for all concerned.


Thanks, and I know what you're thinking, it wasn't me, I've got an alibi!..
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Post Options Post Options   Quote davidyacht Quote  Post ReplyReply Direct Link To This Post Posted: 26 Jan 16 at 4:13pm
Originally posted by gordon1277


What a shame about all the boats lost at Cowes some peoples years of effort in restoration just gone plus classics we will never see again.
Awful for all concerned.

Yep really sad, something we worry about in Salcombe, 80% of the Active Yawl fleet are in two barns, albeit on different sides of the estuary.
Happily living in the past
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Post Options Post Options   Quote gordon1277 Quote  Post ReplyReply Direct Link To This Post Posted: 26 Jan 16 at 4:09pm
Hi GRF
Have a look at a free download called Trueview which allows you to view and plot CAD files.
Gordon
What a shame about all the boats lost at Cowes some peoples years of effort in restoration just gone plus classics we will never see again.
Awful for all concerned.
Gordon
Lossc
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Post Options Post Options   Quote davidyacht Quote  Post ReplyReply Direct Link To This Post Posted: 26 Jan 16 at 4:09pm
Originally posted by Phil_1193

Originally posted by davidyacht

Do you have access to Autocad?  I have some drawings that I did for my N12 with the gybing head sections and profiles in a DWG or DXF format.


Originally posted by iGRF

Regretably no access to autocad........


I maybe telling your granny etc but Autocad files can be 'printed' in PDF and saved/ sent as such

Option 2 is download DWG True View from the AutoCad website, its a free CAD viewer that allows zoom and pan, turn off layers, take measurements etc to the same levels as AutoCad so makes details easier to read

There was a level of how helpful I was intending to be, and do my day job!

In essence our board had a diamond shaped head, which was slightly thrupenny bitted at the shoulders.  It worked fine.  My experience was that the biggest gain was by sailing slightly free, relative to how high you could point, but being really powered up, so in the 12's the biggest gain was if you were heavier, rather than lighter and feathering.

My suggestion to GF would be to make a template of the centreboard case and of the centreboard head section and trim the head section to achieve the desirable gybe angle.

If the board was not loaded up it could slop around a bit.  I know that Ray Rouse's 14 had a device that locked the board when the board was retracted.  There is a view that the boards can "self" steer downwind, don't think that this is a problem on the run, but could be on a reach, but I never found this to be the case.

We used all of the efficiency gains of the centreboard and rudder to reduce the foil areas.  With hindsight probably a little too much, since there was a cost in getting flow going in dead boat situations.
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