Confused on the order to do layup

I am hoping someone can give me some insight on the correct order to layup the fiberglass on my transom. I was okay with patching in the large cut out, but during the demo process I found another horizontal crack (low left by the bunk) and a small vertical crack caused by me being overly aggressive tearing out the rotten plywood & glass. Should repair the lower horizontal crack & vertical crack before patching in the large cutout? If I do it that way, I'm going to grind most of the glass on the vertical crack away to get the 12:1 taper needed for the cutout. Thanks for any insight you can give me!

 

More experienced builders will be able to give you specific advice, but from the photo, I foresee a complete removal of most of the plywood with a router and replacement with a complete sheet of plywood epoxied into the whole transom, then heavy glass Epoxied over that.
Just patching ragged and odd-shaped wooden sections is going to risk future integrity in my mind.

Hint - when you are putting the final outer layer of Epoxy, Glass on the Transom, you can use sheets of Mylar applied over the wet Epoxy to create a very smooth and fair surface when they are removed after cure.

 

Grind away.

Grind that area first, you’ll be glassing over all of it anyhow, so add a little extra in the cracks first to level the surface, then glass over all of it.

 

Clean up the wood, till you are at solid ground. Grind away the cracks as suggested. You will be grinding away most part anyhow, around the wood. Then glue in new wood, and glass over the whole lot, including the cracks. No need to do it in 2 steps, first the small cracks then the large part.

Make sure every hole drilled into your new transom is properly sealed, preferably by overdrilling, filling with epoxy, then drilling the right diameter hole. This will protect the wood from water ingress. (this is what killed this transom very probably)

 

Difficult to tell from the photo, but I’d be real suspicious of the plywood beyond the cutout area you show. Myself, I’d be tempted to cut it all out and start fresh.

 

Is there a good reason to keep the little bit of wood that is left ? It seems that would virtually guarantee a weak core on both sides near the join to the sides of the hull. I would get that all out and have no joins in that area at all.

 

Pretty much what everyone else has said. I would probably remove all the plywood but would replace it with coosa or similar rather than more plywood.

 

Thanks for all the responses!
I'm not planning to keep any of the wood. This was an "in-process" picture not the finished product. I am going to grind it down to fresh glass. The knees are in good shape & no signs of rot, so that is some good news. I was contemplating a Seacast pourable replacement, but now I am thinking Coosa might be a better alternative. I will have to cut the remaining top cap off to get it in though. My thinking is 2 thicknesses of 3/4" Coosa with layers of 1708 & poly or vinyl-ester resin between to get the total thickness of about 1 5/8". The original tansom has some type of structural foam to fill between the skin & 1 1/2" this plywood.

 

If this is a hand layup I’d opt to go with epoxy.

 

Thanks! It is a hand layup.

 

Adding glass between the layers of Coosa doesn’t add much strength, just weight, time and $$$. If using polyester or VE, the most you’d need is one layer of 1.0 or 1.5 oz CSM, just enough to bed the two sheets together.

You could use epoxy, but you won’t gain much in this application.

 

At some point the coosa needs to be joined back onto the existing hull. Epoxy is far superior in adhesion and filleting than polyester for that application.

 

Polyester and VE are more than good enough to last the rest of this boats lifespan.

Thousands of boats are made every year with these resins and the only failures you see are from sloppy workmanship.

Added strength is a bonus when it’s required, when not required, it may make a person feel better, but it doesn’t add value.

To take advantage of the increased physical properties epoxy has to offer you need to start right in the beginning and design every aspect of the build around epoxy.

Mixing the different resins later, and using glass designed for polyester will significantly reduce the advantages epoxy may provide.

 

Secondary bonding with anything but epoxy is substantially weaker. In addition, for most people, there is hardly any practical difference in price between epoxy and VE resin in the sorts of quantities needed for this project.

 

There are secondary bonds in virtually every boat built with any type of FRP, the larger the boat/yacht, the more of them there.

This doesn’t take into account the thousands of commercial and private craft the are lengthened, widened, or heavily modified in some other way (these are mostly large vessels).

99% of these modifications are done by companies that do a great deal of this type of work, and very few use epoxy.

So while epoxy is stronger in just about every way, the added strength isn’t always required for a solid and long lasting repair.

There is nothing about this repair that would indicate anything more than typical polyester or VE resin would be needed.