Replacing Grab handles and toe rails – Deep counter-bore?
When Robert Jones (WOA Magazine Tech. Editor) reviewed my technical article for the 2015 Winter edition he had an excellent question – Did you find any existing fixings where moisture had made it through to the balsa core and if so what did you do? He was tempted to bore through to the inner skin.
As it happened I had given some thought on how to deal with this eventuality before I started removal so agreed to outline the approach I might have taken had I found evidence that the core was wet.
Happily for me out of the hundred plus holes there were only a handful that showed significant rusty or black discoloration around the root of the stud. These were all toe-rail fixings and so were inspected to ensure the stud was still sound and for any other clues that a core failure might have occurred. As the local climate regularly elevates the deck temperature to above 50C and Camomile’s decks have been in this environment for a while I thought it reasonable to assume that the core would be acceptably dry.
Had I found it necessary to deal with a failed balsa core I would have done so on a selective basis by the “deep counter-bore” method described below where stage 1 & 2 are identical to the “shallow” process described in the magazine.
This section through the deck is fairly typical of the arrangement on our Sealord where the underside of the bolt is buried under soft trim and also fibreglass making a method of replacement from the outside only very attractive. I note many Westerlies are happily endowed with moulded in toe rails and handles mounted on plinths.
- Using a reciprocating saw with a small foot and a cobalt steel blade the bolt heads were cut off once they were exposed with a chisel. This process took about 2 minutes per bolt.
2) With a small jemmy & chisels into what was left of the adhesive under the wood the teak was lifted taking care not to damage the gelcoat. The bolt ends were then deburred and covered in short lengths of plastic tube to protect against injury.
3) Then counter-bore over the stud through to the inner core. This would need a long series hole cutter (available?) rather than the off the shelf one I propose in the shallow counter-bore method to allow the additional depth of outer skin grp and balsa core to be accommodated in its throat.
4) Remove the balsa core to a diameter 2-3mm larger than the counter-bore to ensure that the eventual compressive bolting load is transferred squarely to the outer skin thereby reducing the chance of the periphery of the counter-bore subsequently stress cracking from shear load and leaking. This would be achieved with an “L” cutter (much like an allen key with a shortened short end) in a low power/torque battery drill to avoid it snatching as you work your way around the stud. A specialised Dremmel tool might also be available to complete this task.
5) Prepare an appropriate quantity of plug style fixtures to hold the now wobbly stud true in the centre of the counter-bore. I sketched a design for these which is essentially a washer with a small shoulder in case I had to have them made but would need to select a plastic that epoxy does not like to stick to. They would be essential because the pitch and attitude of the studs drilled by Westerly is understandably not accurately consistent and therefore their positions are transferred (per the shallow counter-bore method) by spotting through from the original teak fitting into its corresponding replacement and so hence must be accurately centred. Having removed any debris and thoroughly dried the counter-bore a small amount of slightly thickened epoxy would be injected into the counter-bore and smeared around the bottom of it to ensure that when the hole is filled with less viscous resin it does not drain past the nut (and its possibly porous fiberglass covering) to ruin anything below. Importantly it would also serve to hold the stud in a centred position while the full potting is carried out. The plug fixture would be inserted to hold the stud true while the resin cures.
6) Fit square nuts or an upside down wing nut and hex nut to lock it to the shaft and tighten them together hard as deep as possible in the counter-bore such that they are immersed when potted with epoxy. As with the shallow counter-bore method this is to prevent the stud turning when the teak is fixed in place. Some trial and error would be needed here to determine the best “keyhole surgery” tools needed to lock these nuts together within the very confined amount of space.
7) Once cured and with no leakage detected below the plug fixture would be removed while the counter-bore is potted (with perhaps a mineral filled resin) to within a few mm of deck level leaving a small recess as with the shallow counter-bore method.
8&9) When fully cured the new teak work would be bedded onto masked mastic and squeezed out to ensure a good seal against the gelcoat and teak alike. When the mastic is almost cured it would be soft trimmed and the teak plugs bonded in with epoxy to protect the nut and stud.
This deep counter-bore route needs perhaps a little more time and skill with an additional process to keep the studs in a true position hence why I would have only used it to treat areas where the balsa core was in poor shape. However the only specialised equipment is probably a doctored cutter, a box of turned plastic plugs and perhaps some modified spanners.
As always if you have any questions or need some clarification please just contact me by email.