Keel bolt backing plate replacement


Super Anarchist
So I think before doing anything, clean up the area in way of where the plate will fit onto, and then sit the new plate across it.
The deflection in that plate looks to be significant at the edges, but its important to determine if that's the hull shape or not,

If it is then that's a fair amount of gap for the thickened epoxy to bridge, it might be better to use something like glass fibres to make a repair 'bog', kind of like the type that you get in car repair kits, but with epoxy instead. It should be a lot more stable than just using colloidal silica.

El Borracho

Barkeeper’s Friend
Pacific Rim
Those plates are not thick enough to develop a significant portion of the clamping force out at the far ends. They simply bend. A steel member like that would be from 1/2 or 3/4” plate to transfer a large bolt load to the ends. At least in farmer rule-of-thumb eyeballing’. However moving the load out there might endanger the structure.

My own rule is to renew what was there without change if it worked well enough for many years. Perhaps more modern sealant, tho.

Sea Scouter

In 316 it's about $25 in 1/4" material. If you brought the stock to any small shop, sawing to length, drilling, and busting the corners is a 1 hour job. I would charge about $75. It would be $100 if you watched and asked questions. You need somebody with a real mill or a drill press... not the home gamer shit. Yes, epoxy bed them and allow a couple days to harden up.


Overlord of Anarchy
San Diego
It's a backing plate over the keel - I think 1/4" is too thin. Not sure of exact dimensions, but it looked like maybe 5" in length? I'd go with 3/8" at least, weight is not a concern


New member
I thought I'd post a note just to say 'job done' and, in case anyone else is facing the same problem, and wondering whether to tackle it or not, it wasn't that bad, if I can do it I expect you can.

I got lucky and happened to be emptying my rubbish at the same time as the boatyard owner and veteran sailing barge skipper, who has spent his life dealing with larger-than-yacht size pieces of stuff. I told him I was trying to figure out how to form the backing plates to the curve of the bilge and he said he'd help me. Some delicate work off the boat, with a sledge hammer, an anvil, a couple of half inch plates of metal to form a bridge, and an 18 inch long, 2 inch wide steel pin to transfer the load, and we (he) had a set of matching plates that just dropped in and fitted. This meant that there wasn't any bridging across the low part of the bilge and all of the threads on the bolts were exposed and the epoxy wasn't going to have to do more than fill irregularities in the layup (of which there were plenty).

After that it was proceed as planned, i.e. 'dry fit' in bed of epoxy, then bed in sealant.

When removing the old nuts it was obvious that some were looser than others. This makes me wonder about the wisdom of burying these things beyond reach under gel coat/fibre glass. Friends of mine have 'quality' yachts which have had it done like this, but it doesn't feel right to have things that can't be checked. I've seen it written that the gel coat covering is to keep the water from getting into the threads but I'm not sure how real in issue that is going to be if one has used grease/anti-gall when installing, and its easy enough to slaver some grease in the general area, to keep water out without hampering maintenance.

I'll give them a check once the boat has been sailed, for the time being I'm on to other things.

Thanks again for all the advice, it gave me the confidence to proceed.



Super Anarchist
Great Wet North
Looks skookum.

Burying nuts and bolts in glass is dumb. Water can probably get in unless a very careful job is done and then corrosion proceeds in the dark with little oxygen.
No probably about it - water will get in.

One of the things that I learned from 50 years of living in a rain forest is that you can never entirely keep water out, you can only trap it in.