Composite Question, filling transom holes

[foca]

Looking for some knowledgable composite guys out there, thanks in advance:

I need to perform some repairs on my transom. I have a pair of 3" diameter holes, where the original engine control and fuel lines ran through. They are located at about the center (on both axes) of the transom. They are evenly spaced and at the same vertical level from the bottom.

My transom is quite thick, about 2-3 inches. I also have some delamination of the top layer of glass on the inside. This layer is about .25" thick. My plan is to grind away all the lifted fiberglass and get to the good wood, then lay up several layers. Does this sound like the best idea? what kinda of glue is best for this? Also I have some lag-bolt and through-bolt holes to fill from the transom bracket i removed. what's the best method for this?

As for the holes. I was gonna grind out around the holes to create a dibit. Then layover a couple times on the inside and outside, then drill a small hole and fill with something. what should I use to fill? I would like to use something strong enough to support structurally as there will be no wood there. I heard about some stuff that is used to replace rotted wood in transoms. The wood is hollowed out of the transom leaving only the glass "skins" and then they pour this stuff in. anybody ever hear of this? what is it?

Picts available upon request. Thanks again everyone.

[Corpus Skipper]

My plan is to grind away all the lifted fiberglass and get to the good wood, then lay up several layers

So far, so good.

what kinda of glue is best for this?

Epoxy is best, but poly or vinylester will do, especially if the boat is trailered.

Also I have some lag-bolt and through-bolt holes to fill from the transom bracket i removed. what's the best method for this?

Taper the holes out to the outside with a fine grinding bit, then feather the gelcoat and 'glass back around the edges about 1/2" around the holes. Fill the holes with epoxy putty (back up the inside with duct tape) and smooth the outside with a plastic putty spreader. Sand smooth.

As for the holes. I was gonna grind out around the holes to create a dibit. what should I use to fill?

I would just cut out plywood circles the same diameter as the holes and 'glass them in same as you described. Be sure to cover all the wood with resin, especially the edges. Wouldn't hurt to 'glass the inside 3 or 4 inches past the patch on the inside. I've heard of the transom goop you described, but haven't seen anyone use it yet. I'd imagine it's pricey, and probably doesen't give you any better results than using the plywood plug. You'd have a hard time laying up the outside 'glass, and leaving a void to fill sounds like more trouble than it's worth. It'll all be sealed so it won't rot. Use epoxy for the best results. Good luck!

[PAR]

The transom goo (SeaCast) isn't something I'd recommend yet, though they did finally email me the weight and compound type.

As I suspected, it's a poly resin, designed as a core material, rather flexible and heavy around 50 pounds a cubic foot. The key here is it's a core material and the skins have to be sound and clean for a good bond just like any core material. It seemed like the flavor of CPES that's cured in the bottom of the pot.

The sample I have has two thin 'glass skins and is quite flexible, but there are much better core materials that are much lighter and make much stiffer panels in sandwich construction. A flexible core sandwiched between reasonably stiff skins of 'glass doesn't make me feel all warm and fuzzy. Something's going to move, then separate from the skin(s) and now you have a flexible goo floating between two much weakened skins. Core separation will dramatically lower the strength of the panel.

The advertising fluff that came with the sample said nothing about the properties and after several months waiting, they've indicated those properties are "in the mail"

I'll hold my breath.

I also don't recommend poly or vinyl for transom repairs. The core will have some level of damage from moisture and a really good, strong bond is what's needed and epoxy will serve this much better. Poly could be used over this to defray some finishing, costs. Odds are there will be damage to the plywood core and that will need addressing, if any time has past with the core exposed. If not, and a good wood can be had, a good "lick em and stick em" of plywood circles (with epoxy) and filling with layers of cloth/mat and paint. Make sure to really grind back well around the areas being patched (several inches), so you have plenty of bonding area and room to feather back into the transom.

[foca]

guys,

great info. I appreciate the time you took to reply. Actually, I also ordered a book "The Fiberglass Boat Repair Manual" by Allan H. Viatses. Anyone familiar with it? crap or worth the read?

I got into it bigtime, this weekend. looks like ~80% of the transom is rotted. As sad as it sounds, if that was all i had to worry about, i'd be happy. looks like at least 2 stringers are bad and one is good, there are 4 total. One of the bad ones is a main (lower) one, and probably the other one too, that was the only one I did not get into. I'm in trouble. This is now a HUGE project, but i guess there is no turning back. I've been a little bummed about it all weekend, but it is what it is. I'll get it done.

As for the transom, I was thinking about cutting the upper half off, from the inside. This will give me access to hollowing out the bottom half and filling. Outside skin stays intact. but you guys say you don't have confidence in the transom filling options. BTW, i will be plating the inside and I am running a dual engine bracket. And I am still faced with having to now core the upper half. That will have to be sections of plywood. Or, if there was a good filler option, I could add small sections of wood to locate and hold the original cut skin, and then fill that. Big question mark on this one.

Then, there is still the stringers. I am pretty set on removing the tank access cover and the tank to check for cracks. I should probably see how far forward the rot goes in the stringer. but then, what are my options? The floor covers the top of the stringers, so the only way for me to get to the inside, would be through the side of them. should I just leave them alone and lay up some more on the outside of them, and as far forward as possible? mindset being, if they haven't cracked so far, they would be fine with a little glass reinforcement. I can get to the aft part of all four stringers. I can take the tops out and hollow them, but only the back 2-3 feet.

would it be possible that this stuff is balsa? it's wet and i can push a screw driver into it, but it's not totally falling apart. I know balsa is soft, so is wet balsa just a little softer? should I dry it all out and see how it looks?

Thanks again guys. you are life savers. hope everyone had a good fourth.

[Corpus Skipper]

Actually, I also ordered a book "The Fiberglass Boat Repair Manual" by Allan H. Viatses. Anyone familiar with it?

I have this book, and it is filled with good information. It addresses all of the issues you've come across, and should help you out a bunch.

[Black Swan]

You may well be faced with a complete transom rebuild, and if you've got stringer damage it may extend back into the transom. It's a big job, but if you've got that kind of rot, a half fast approach may compromise your safety. Stringers are highly unlikely to be balsa. If they are, the manufacturer should be keel-hauled, drawn and quartered, then fed to the sharks! IMHO the only way to address rot is to eliminate it... completely. It has been my experience with rot that sometimes the whole floor has to come out, stringers dug out, new stringers (or partials) fitted or scarfed in, then glassed or epoxied in. Most often the repairs represent better construction than the original. Good Luck!