Gybing Centerboard

[ifoxwell]

Hi all
We are looking around for our first 12...
3402 is for sale and has a Waller gybing Centerboard
Does any one know this boat or had any experiance of these boards?
Cheers
Ian

[icecreamman]

I do not know if it is of any use, but there is a good article in the Hornet association forms.
http://www.hornet.org.uk/forms/20051113104700centreboards.pdf
As they say it is part of the black arts, and whilst I understand some of it, I have never used a gybing centreboard. Good luck!!
 

[samlaw]

Only quickly scan read the document but as a physicist my initial interpretation is...
 
Don't think of it as the rotation the centreboard but a rotation of the hull to point in the actual direction it is travelling. First instinct would be that the main gain would be that the hull shape will work more as designed (no side ways flow of water against it) reducing drag.
The effect on the rudder is a seperate consideration.
I also suspect the "trim tabs" of DCB have made these obsolete anyway. Though have no idea of what exactly is meant by trim tabs, I assume some kind of flaps to make the CB a Assymetric rather than symetric foil to generate lift at 0 angle of attack.

[Antony (Guest)]

Ian,
 
The simple answer is that all (or almost all) of that generation of Final Chapter had those boards, mine (3384) certainly did.  I have no strong view on whether they help or hinder your progress to be honest - i did not rush to put one on any other 12 i subsequently had but did not take it out of 3384.  On balance my personal view was that they slightly accentuated the already open water bias of the design, that is to say that the Chapter shape and the gybing board are both a disadvantage in light winds and especially when doing things like lots of roll tacking.  A sistership (3395) won the Burton in 1994 and that boat and others had plenty of good results in their time.
3402 looked good last time i saw her, and her previous owner certainly seemed to do a nice job on putting in the floor.  For your purposes it seems to me that you are best off with a Chapter or a D8, the D8 is probably the easiest boat of that generation to sail close to her potential whereas the Chapter (and indeed arguably the Baggy) have greater open water potential when sailed well.  All that said, a D8 won two Champs and a very similarly shaped Crusader won at least one more (no history book at work).
Finally, and i know you are not new to buying sailing boats so this might be a statement of the obvious, remember that the kit in a 2nd hand boat is worth a lot more than the hull.  In 3162 you are virtually getting the hull for free, and with any of the boats in this price range you are paying for carbon rigs and decent sets of sails as much as anything.
Any more questions email me,
Antony
N3348, but ex-3123, 3208, 3286, 3384, 3431, 3447, 3484 and 3514...

[Tom Stewart]

Antony,
3395's Board was very stiff in the case and I don't believe it ever gybed!
I don't like the idea of altering the angle of attack of the board but the Ex 505 World Champ who sits across from me wouldn't be with out a gybeing board.
I certainly wouldn't let it put me off the boat as stopping the board from gybeing is very easy.
Tom
(3003, 3348, 3372, 3395, 3426, some more feeling foolishes 3513, 3526 now being fitted out)

[samlaw]

altering the angle of attack of the board

 
Sorry Tom, but am not sure that statement is correct. The cetreboards angle of attack does not change, the Hulls does. But only strictly true in the limits, lateral resistance by CB >> lateral resistance by hull.
 
I may be wrong, please correct if so.

[johnk]

A lot depends on the hull shape. If the extra drag on a hull when it moves at a small angle to it's line of fore and aft symmetry is negligible (think Topper), there is no point in a gybing board.

When the extra drag is large (say Uffa King), then by angling the c/b to the hull so that the hull moves along it's line of symmetry, the hull drag can be reduced significantly. If the extra drag on the c/b is less than the hull reduction, use of a gybing board makes sense.

[Solid (Guest)]

Ahh the great gybing board debate.  If you were to throw in the lee bow effect, and the question as to whether the sea breeze follows the sun you could have three of the greatest never ending arguments all in one thread.  If any of our American friends were to drop by we could have the great TOT and TOD debate and we would have pretty much cleared up all the significant yachting mysteries.
 
Nigel has certainly put together some well built boats.  Most of those Chapters were never very square, but they didn’t seem to suffer from it.  I’d be interested to know how heavy it is before jumping in, that may not be a problem depending on the price and what you’re planning to do with it.

[andymck]

mm, thought the angle of the hull was governed by the highest point you can get sails to set, so hull angle going to have to be pretty similar. This may be an over simplification, but seems obvious. The centerboard angle must change to that effective point of reference. What it may do is effectively allow you to sail lower, while maintaining your centerboard angle the same as a conventional one. Either way, its the sails that set the angle the hull can be set to.

Andy

[Derek]

The reason nobody has ever got to a definitive answer is because it is "very complicated". You have two sets of aerodynamics in two different fluids with radically different densities and reynolds numbers. The two angles of attack are interdependant.
Add to this the fact that it is meant to work over a wide range of speeds and wind conditions and you can see why you could write for years and never get a straighforward answer.
As Tom and Ian have identified though, it seems to be a feature which finds more favour with faster boats rather than a 12 where a sudden change in board angle might just throw you in the water downwind. Didn't some of these boards gybe only when fully down? That would seem like a good solution..
Derek

[DavidYacht]

We had a gybing board on Annie Apple, wobbling downwind was never a problem.  There are times that a gybing board is very quick, particularly if you foot and have enough power to drive the boat, in effect you end up pointing slightly freer but the gybing board is clawing you to windward.  It is quite hard to consistently find the sweet spot.

[DavidYacht]

All you ever will need to know!
http://www.usa505.org/wiki/index.php5?title=How_Gybing_Centreboards_Work
Follow the links from this page
David

[Martin]

Annie Apple is sailed at our Club.  Was it sold with the gybing board intact?  The current owner hasn't changed anything but from memory it doesn't look particularly different to a normal board apart from the control line arrangement.
That boat goes like Joe Stink on our little puddle, particularly in light winds and carries weight much better than my Foolish.  In those conditions very hard to keep up with, let alone beat.......

[DavidYacht]

Nice to hear she is still going well.
If you look at the board it should have a diamond shape head section.  I put quite a lot of effort in building up with epoxy & microballoons to eliminate any uneccessary wobble.  The centreboard uphaul downhaul system was as much about putting some friction in the system because of the reduced surface area of the gybing head.