centreboard repair advice
16/02/2019 at 11:42 am #17417
Last summer I was given a GP14 – an old club boat that hadn’t been used for some years. It’s a grp boat, I haven’t located the hull number yet but I think it’s a 1980s mark 2. I replaced some halyards and took it out a few times – all seemed good apart from the centreboard refused to stay down. I have removed it with a view to replacing the centreboard brake (the rubber tube has become quite hardened) but I see now it needs some more renovation. It’s been repaired in the past – looks like it’s been taken apart at a joint down the middle and re-glued. There’s also a split across one of the boards that has been glued. Both repairs appear to be holding up – but there are a couple of new gaps opened up between the joints at the top of the centreboard. The belt and braces approach would be to take the boards apart, plane the joints and re-glue – but I have neither the tools nor the expertise to do this (and I’d probably cause more damage in the process). Instead I’m looking to patch it up again, sand and revarnish. I’ve searched online, but the advice is varied and conflicting. My options are:
a) work some epoxy into the gaps and use clamps to close them up as much as possible while it sets. I have some large sash clamps that would do the job. My only concern is that it I’m not sure how much the gaps will close, and if they do it would leave the wood stressed. Is this going to be a problem?
b) I’ve read somewhere that gaps like these, at the joints, are due to shrinkage and sometimes close up again when the boat is in the water more regularly. The advice is revarnish, but not worry about the gaps. I’m sceptical about this. The gaps are at the end that won’t be immersed in the water. Some suggest using a flexible filler in the gaps in case the boards expand in future.
c) fill the gaps with thickened epoxy and revarnish.
Any thoughts? I’ve attached some photos.
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16/02/2019 at 1:17 pm #17423
This centreboard is very well constructed, but the splits are one of the few glued joints where the joint is actually stressed, i.e. where the “handle” meets the body of the board. You are absolutely right that the proper way to repair this is to take the joint apart, clean it up, and re-bond it with epoxy. However because the joint has already started to split it may be less of a problem than you suspect. It may also be a case of using your contacts and the camaraderie of your club to ask whether anyone in the club can give you a hand with the job.
Almost anywhere else on the centreboard the joints are under very little stress, and it might then be worth trying a suitable flexible filler. But I think not here, unfortunately!
It would be well worth at least trying to split the rest of the damaged joint. If the wood will come apart into two neat pieces the job is relatively easy. Since the joint is tongue and groove (as seen on one of the photos, showing an end view of the joint) you are unlikely to be able to plane it without access to either the specialist plane or a suitable router or spindle moulding machine. However you can at least clean up the dirt and grot from the inside of the joint, using a sharp scraper, or a sharp knife, or a sharp chisel, held more or less perpendicular to both the wood surface and the grain, and then dragged bodily along the grain. Note my deliberate insistence that tools should be sharp, and by that I mean seriously sharp; it pays dividends to resharpen your tools frequently, and this is a skill worth learning – and again there is at least a good chance that you may find someone in your club who would be pleased to help you there.
Then you can reassemble the joint, bonded with thickened epoxy; coat both sides with neat (unthickened) epoxy, and then while this is still wet coat one side with thickened epoxy, assemble the joint, and clamp the two parts together with a pair of sash cramps.
That is straightforward. The big risk is that the joint may not split cleanly, and you may end up by splitting the wood rather than splitting the joint. You can do a lot to mitigate that risk by driving a (seriously sharp) chisel along the unbroken line of the joint, on each side of the board, in order to force the joint apart; since the joint has already failed at one end it is reasonable to expect that at least the part of the joint which is reasonably near to the split is itself not far from failure, and your chisel can provide that additional impetus. However don’t try to chisel through the tongue in the centre of the joint; that would be trying to cut through undamaged wood rather than failing glue. The tongue may or may not come out cleanly; but if it splits, at least that indicates that it is still strongly bonded to the adjacent wood, and the splits in it will be clean and will provide a good surface for epoxy to bind to when the joint is reassembled.
If you end up with part of the joint remaining unbroken, and the wood splitting instead, all is not lost. The likelihood is that this will be at the far end of the joint, where the load will be least; and (as with the tongue) the split wood will make a good clean surface for epoxy to bond to. Simply remove any part of the split wood which is going to actually obstruct the joint from fitting back together again, and then coat all broken surfaces with neat epoxy, overcoat while still wet with thickened epoxy, and proceed as before. Thickened epoxy is an excellent structural gap filler.
Once the joint has been reassembled and the epoxy is solid, clean off any surplus from the face of the repaired centreboard. If you manage to catch it at the point where it has become solid but has not yet fully cured you can cut off any protruding surplus with a sharp chisel held flat to the wood; if you wait until it has fully cured it is much harder work.
Once the epoxy has fully cured – and don’t be tempted to try this while it is still soft – sand it flat with a orbital sander.
Hope this helps,
- This reply was modified 5 months, 1 week ago by Oliver Shaw.
16/02/2019 at 6:29 pm #17425
Thanks for such a detailed and informative response Oliver. There are actually two cracks. The most serious is near the handle itself and runs along the joint close to the trailing edge of the centreboard. On close inspection I see this joint is failing almost along its entire length so I will have to bite the bullet and break it apart here. Due to the tapered shape of the centreboard, it will be quite thin at the bottom end so I’ll have to be careful. The other gap is nearer the centre, at the centreboard brake notch. It’s narrower and only about 5 inches long, and may have been caused by the screw used to attach the brake. Below the gap, the joint seems very solid. I’m wondering if I might get away with epoxy and clamping this one, without taking the board apart in a second place?
16/02/2019 at 8:24 pm #17426
The smaller crack, first: if we are thinking of the same thing – the very small one which I see across a screw hole, I agree that this does not need any dismantling. I would be inclined to clean it out with a very fine saw, either a hacksaw or a coping saw or just possibly a dovetail saw, so that you have a good clean surface. Then fill it with either epoxy or a flexible mastic. However there appear to be several screw holes in that recess, so if it were me I would be inclined to drill all of them out to either 8 mm or 10 mm, and then let in teak plugs (obtainable from good yacht chandlers) bonded in with epoxy. Then your replacement screws will be going into new wood. Do all the cutting first, then fit the wood plugs, and finally fill the crack with either epoxy or mastic.
Note that wood plugs differ from dowels in that the grain is across the cylinder of the plug, rather than along its length, so you are not going to end up screwing into end grain.
On the bigger split, don’t worry too much about breaking the thin wood at the bottom end; if it does break up you can regard that as a non-structural cosmetic detail. Depending on your skills and your wishes you can either let in a small piece of new wood and then fair it in, or you can repair any blemish with filler.
Hope this helps,
18/02/2019 at 7:51 pm #17453
Thanks again for the advice Oliver. Need to order up a few bits and bobs before I start, but will let you know how I get on.
20/02/2019 at 4:57 am #17465
even if the wood does not split cleanly, epoxy and a few clamps should still rejoin it nice enough to cover in varnish again.
My series 1 GP had a similar crack at the handle, but mine was a solid board, not one that was put together with tongue and groove. I epoxied mine, used a bit of glass cloth to reinforce it, put a few dowels into the leading edge to stabilize it, and then painted the entire board as I also had many nicks and deep gouges to fill. Similar to your boat, Spark is an ex-club race boat and time and previous owners had not been kind.
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20/02/2019 at 4:58 pm #17469
All good advice – use white cellulose fibres to thicken the epoxy (SP106) not the brown colloidal silica. Make sure the wood is perfectly dry before you start applying the epoxy and wipe off any residue with acetone before varnishing or painting. Another way forward would be to keep an eye out for a second hand centre board from a boat that has been scrapped – Ebay or the Assn Classifieds – you could put a wanted on the Assn Classifieds – there will be a number of old bits in members sheds!!
20/02/2019 at 8:17 pm #17470
A secondhand board is indeed an alternative way forward. But if you choose that route do make sure that you get only a Series 1 board; I understand that the later Series 2 type won’t fit.
Perhaps fortunately, I would guess that Series 1 are the more likely to come up secondhand.
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