tricky transom delamination repair

[spoolin01]

I'm new to fiberglassing, and I think I have a bit of a tricky repair situation. The fiberglass skin delaminated in a couple of places from the backside of the plywood-core transom in my Achilles SU-16 inflatable. The tricky part is that the delamination extends down below where the floor rubber wraps up and around from underneath. So what I've got now is an 8" half moon area above the rubber line where I've ground the glass down to the wood and out to where it's solidly bonded to the wood, and a roughly equal half moon area below the rubber line where the rubber is firmly attached to the skin, but the skin is pulled away from the wood. The wood is good, no rot. I really don't want to detach the rubber to fully remove the delaminated skin - it's tightly glued now and I'm leery of being able to rebond the rubber to new fiberglass, and of trying to work behind a stretch of partly detached rubber. If I glue the skin back to the wood with epoxy resin, I'll be left with a butt-joint with the epoxy and glass repair of the area above the rubber/skin edge (the skin is maybe 3/32 thick). In retrospect maybe I should have cut the skin well above the rubber line so I could taper it and glass up onto it... I guess my question is, what is the best way to deal with the joint that's going to exist where the old skin is glued back to the wood, and the newly exposed area above is re-glassed? I could extend the new glass for the area above the rubber line to an inch or so down behind the skin before glueing it down, so there would be some area of glass for the skin to bond with, and avoid a total butt-joint at the skin-edge. I'm assuming if I leave a butt joint between the old skin edge and the new glass above, that it will just flex and crack. I guess I could also trim the rubber edge back an inch or so and lay a piece of cloth over the top of the joint as well. My other thought was to put a fillet of thickened resin at the butt edge of the glued-down skin, and feather it out onto the (wetted) fresh wood above, with some plain resin over it. That would give me an area to glass up on to. I just don't know which approach gives a better bond - old skin directly to wood with nothing but slightly thickened resin, or old skin with a band of glass behind it along it's edge.

As I said, I'm new to glassing so I'm hoping for some experienced advice about what to expect and how to proceed.

Mike

 

[jonesg]

Re: tricky transom delamination repair

sounds tricky, maybe you shoulda left the outter transom glass skin alone.

But the transom shouldn't flex anyway, so having a butt joint shouldn't be an issue. I would leave the rubber alone, you have a decent idea to run a layer down between the glass outter and the wooden inner.
Can you add thickness to the inside of the transom?

 

[spoolin01]

Re: tricky transom delamination repair

There was a split in the skin running for about 6" through the delaminated area and down behind the rubber, I was thinking I needed to seal things, and keep the delamination from propagating out - just guessing there that that would happen, I don't have much experience with fiberglass repairs. Maybe a minimalist approach - opening the crack a little and just filling the void with resin and clamping - would have been better. Since this is an inflatable, I'm hoping the transom itself doesn't flex much under load, that the tubes and joints give instead. When you say to add thickness to the inside of the transom, are you talking about stiffening the transom from the inside? That would be possible - would you use glass only, or laminate more wood and glass? The transom is about 2" thick. A friend has also suggested packing the gap between the skin and the wood with some thickened resin rather than clamping it close together while gluing - he didn't explain why increasing the resin thickness there would help.

thanks,
Mike

 

[spoolin01]

Re: tricky transom delamination repair

I ended up making a GRP sheet using 19oz Knytex X-Mat sandwiched between two glass plates with some weight on top. It came out around 1/16" or a little thicker. I trimmed it to shape as best I could but some gap around the edges where it fit down behind the old rubber-covered skin couldn't be avoided. I left plenty of room above to transition into the taper of the skin that was still in place. It stuck up maybe 3" above the old skin line, and about the same below it, with some relieved semi-circles to match the drain holes. Before inserting it I wetted down a layer of 6 oz cloth cut to fit the exposed area above the cut skin and down maybe an inch or a little more behind the cut. When that was tacky enough not to get dislodged, I inserted the GRP plate and poured some slightly thickened resin in front and back of it and clamped along the stretch of rubber/skin. I laid a piece of 9 oz cloth to butt against the cut line and transition into the taper of the ground out perimeter, covering over the upper half of the inserted piece, and then completed the transition with a piece of 6 oz cloth, similarly butted against the cut line. After fairing it, I gave it another coat of resin, then painted it. The fiberglass formed a cove along the butt with the rubber which so far has held together fine. I've had the boat out for long trips in rough water a couple of times now and so far so good. It was a long project though and if I had it to do over, I'd have just injected a bunch of resin and clamped it together. Live and learn...