Suggestions please for mending small hole in under-water planking...

[Nige123]

As per pic, found a weeping leak which when traced led to the excavated mess - "main" through hole roughly 2" x 1". Seems someone didn't bore the hole accurately for the bolt that goes up to the engine bearer - evidently had two goes as the hole was elliptical and filled with gunk on the overcut side (white lead?) before the inevitable happened and rot started. It was a threaded bolt as well... Rest of the plank is sound on all sides - 3/4" mahogany - just looks off-colour as the wood has absorbed 80 odd years of some black primer / tar mixture (realised this was the case some years ago when scraping the lot in hope of a varnished hull).

Question is, what's the best way of fixing this without scarphing in a new length of planking? (Which I don't want to do unless last resort as the rest of the plank is fine, rot has been caught / wood treated, and to get the bolt out I need to remove the engine & gearbox etc etc). The boat is only used on inland waterways and this is a flat run of planking so it's not going to be stressed unduly in a seaway for instance; it has a very quiet life!

I thought about using a hole saw to enlarge the hole to the right of the bolt and then epoxy in a mahogany plug ensuring grain in same direction, coating the inside (i.e. bilge face only) with a couple of coats of Danboline then encapsulate with lot with epoxy on the outside. The sistered ribs inside will stop it being pushed through and there's an engine bearer on top of them so any butt blocks etc. are out of the question. Can make up some epoxy filler to bring the planking around the hole up to surface level and minded to epoxy in the bolt above the gunk that is sound; with a bolt that size the plank / engine bearer relationship is fixed irrespective and I can't think how else to fill the odd gaps.

Does this sound workable? Has anyone a better suggestion?
Many thanks.

 

[Gordonmc]

I had a similar problem with the chainplate bolts on a Hillyard where the mahogany topside planks had rotted from the inside. Fortunately only a few mm around the bolts.
I cut back to solid wood in a wedge shape and cut corresponding wedges in iroko about 15 cm long. Epoxied in and cut new holes for the bolts. Of course, I had the luxury of being able to remove the bolts, but you could do the same with a wedge drilled for the bolt and cut in half through the hole radius.

 

[Wooden Boat Fittings]

Well, I guess we both know that it's not the 'right' answer, but on the other hand it would probably serve. But, you need to make absolutely sure that absolutely all the rotten timber (and then a bit more) has been removed first -- ny softness left behind and the rot will continue. Once you've done that, treating the whole raw surface with CPES will not only seal the wood fibres but will allow excellent adhesion of epoxy filler.

Mike

 

[wrr]

I have three concerns about that bolt. Firstly, it appears to be stainless, below the waterline and exposed to leakage. I would try to examine it carefully for crevice corrosion. Secondly, it may be difficult to achieve a strong and waterproof bond between it and your repair. Thirdly, although the timbers will prevent inward displacement, the bolt may vibrate or push the repair outwards.
Ideally, it should be removed and a dutchman (graving piece) or scarphed section of plank glued in place, butted and mechanically fixed to the frames followed by reboring for a replacement bolt. Alternatively, as suggested you could make the graving piece, bore it and cut it in two through the hole so as to surround the bolt when it is inserted. If the timber has been wet, a polyurethane glue may be better than epoxy for the timber to timber bond, although G-flex epoxy is claimed to work in these conditions. With a diamond-shaped piece, tapered inwards and the frames behind it, it is unlikely to push inwards. However, were it to be pushed outwards, the results could be disastrous. I would reinforce the repair with a generous faired piece of timber over it externally, glued and mechanically fastened to a few frames to prevent the graving piece being pushed outwards. I would still regard the repair as temporary, until such time as you can remove that bolt so as to allow for a permanent repair. The forces acting on the bolt would determine if a local repair would be enough or if a section of plank should be replaced as the permanent solution.
Sorry if that sounds pessimistic but I would not take chances below the waterline!