best way to cut out wood core around thru hull

alk

alk

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My ski boat has 3 inch exhaust which comes thru the transom. The build was not great, as the wood core runs right up to the edge of the cutouts. A bit of rot, which I was able to dig out - but where the wood did not rot I would like to cut it back a bit and glass over before I put the exhaust back in.

The glass on both sides is in good shape, and I believe the rot was mostly contained. So not interested in peeling the transom back and starting huge project the week before memorial day. But I would like to go a bit beyond just "painting" the remaining wood with epoxy, and get a 1" or so circle of glass around the cutout, which would allow the bolts for the exhaust tips to stay out of the core. I've hear a bent nail in a drill, but that seems a bit rough. Dremmel, multi-oscillating tool, router, drill, hammer and chisels?

Anyone have any luck removing the core around a 3" whole, without damaging the glass? If so, any tips?
 
I think you'd be better off using two hole saws from the inside.

First mount the 4" hole saw on the shaft, then the 3". the 3" will act as your guide penetrating the fiberglass and the wood. Then re-glass the area

Or, if you only want to pull say 1/8" of wood, I'm thinking only a dremel would work....or a small angle drill with a drill bit...or a small grinder with a 3" wheel...put the wheel between the fiberglass and ream it around.
 
I think I'll give the dremel a try, with cutting bit. I want to preserve both pieces of glass, in and out, and only remove the core.
 
Dremel or router then fill with thickened epoxy
 
In the past in have seen people use a bent 90 degrees screwdriver blade in a drill to route out the core while leaving the two shells alone.
 
That may be work with mushy balsa core... better hang on that drill with any sound wood.
 
I think my approach is flawed - on the port side where the core was rotted, the removal was essentially done for me via the rot. I cut out the little that I needed to with the dremel. But even with the thickest epoxy I can mix, there is pretty much no way to fill the void from below and have the epoxy stay in place. Bottom half is fine I think, but top half - from 9:00 to 3:00, don't see how I will get the wet epoxy to stay in place, and at the same time adhere to the glass sandwich still in place.

I suppose if I had the exhaust tip in the transom, and access from above, I could set the epoxy in place. But don't see any way to fill the 1 inch transom with just glass. I suppose I will cut some small pieces of marine ply to give the glass some strength where the bolts are - and then plan for a proper repair after the season.

On the sb side which has no rot, instead of cutting back past the bolt holes. I will probably just over size drill the bolt holes, fill with epoxy, redrill to proper size, and bolt everything up.

Now for the contentious question. Caulk? I used to always use 3M 101 ( Polysulfide) for anything that was held in place with fasteners. I know some use a polyurethane like 4200 for this application, others use Life Caulk, or whatever the newer polysulfide is called. Any preferences? These exhaust tips are below the waterline, which helps make the decision.
 
Just a thought, Andy.
Drill a small hole from the inside of transom. Wrap the exhaust tube(s) with wax paper, and insert. With a syringe, inject your epoxy.
Hopefully, you can remove the tube(s) after setup.

Edit: Why not forget the wax paper, and epoxy as above. They may never come out again, though.
 
That might work, but I don’t think I want to glass them in, as I will probably pull this apart next winter and replace the wood. It’s not a huge section that is rotted, but it’s close to where the stringer meets the transom, which causes me to worry a bit. More I think about it, I might just fix it the right way now, even if it costs me a weekend or two.

My other boat ( same wellcraft you saw in my driveway dozen+ years ago) is already at the marina and ready to go, so I suppose I should be more patient.

edit: The proper fix is going to have to wait. At lunch today I taped up the edges of the exhaust hole, and via the bolt holes shot as much epoxy into the 'sandwich' as it would take. This should provide enough strength to tighten down the bolts on the exhaust tips and seal the leak I am trying to solve, as well as prevent what's left of the core in this section to rot any further. thanks everyone for the suggestions.
 
If your epoxy is thick enough it it stay and stick to the skin at least long enough so you can put some duct tape around the top part of the hole to make sure it stays in place while curing. Or fill the bottom half and after that s cured put duct tape along the upper part, drill a 3/4” hole at 12 0’clock and fill thru the hole with epoxy wer enough to flow
 
I'd think fiberglass resin and some cut up cloth would hold fairly well. Perhaps a balloon or a plumber's inflatable test bulb could help but be sure to wrap it with something the epoxy won't eat up. After Sandy I had to do ALOT of fiberglass repair and found that layering worked well, I'd hit certain spots every day until they were over built and grinded them down.
 
If you can get your hands on some coosa board, I would inject thickened epoxy into the void and back it up with epoxy wetted coosa. Excess can be trimmed to the hole size. West System 610 is what I used in a few places and it went in and stayed put until I jammed in the coosa. Coosa comes in many thicknesses and it is quite durable. Two half inch layers might be easiest to work with. Dry fit the coosa then wet it down, get the thick stuff in and reinstall the coosa.
I would be leary of filling with nothing but epoxy depending on how deep the void is.
 
I am a jackass that created a user name on a Boating forum so that I could post a link to my log splitter in a thread about a hull repair. My post is completely pointless and irrelevant, but please give me the attention I crave...

-Moderated by the grumpy Admin
 
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