TOPIC: Transom replacement

Can someone explain to me why when rebuilding a transom or replacing one the same mistakes are made over and over again that the original manufacturers made.
Use “marine” grade plywood, chipboard, regular treated plywood etc. sandwich a layer of glass mat in between two 3/4” boards for strength and then enclose the entire rebuild in an airtight enclosure of fiberglass. After all the efforts of getting it water tight the very first thing that is done when finished is to drill holes in it for motors, drains, etc. thus getting water right back in. Might as well put a piece of plywood in a baggie, fill it with water, store it in a dark damp place and expect the plywood to dry out. I’ve done this many times with outboard transoms and two I/Os. You can “seal” the holes with silicone or epoxies but water still seems to sneak in. After all efforts condensation will do what is trying to be prevented. Not trying to promote composite (poured) replacements but keeping it “original” is just asking it to fail again. A few weeks back I attended Andreas' Thompson boat rally and after looking at all those wood boats the transoms are solid - open - not incased and some are original and just as strong as if they were new. A fresh coat of varnish for cosmetics.
Case in point is the transom I replaced on this ‘76 Starcraft American 15. You can see the futility of putting a layer of glass mat between the wood.

Good question, but 1st reality is we are old & even doing it the same way again, we'll be dead 1st.

It seams outboard transoms fail faster. Probably because they flex more simply be design and I would guess more water can enter along the top edge where it is typically enclosed on an I/O.

Perhaps solid glass plugs (maybe 2 inch diameter) counterbored into the transom where the engine mounting bolts go before the inner glass skin is installed would help.

Personally, I'm grateful that the forward-thinking manufacturers used that method to insure that I'll have a job. At my age, it's only logical that I have decided to switch to pressboard or flakeboard for transoms in order to pay-it-forward to future restorers. Cal...I understand your pain. Better take two Midol and get some rest.

Hey Jan, good thinking on your part. Sorta a "I'll get ya again".
Of course when I replaced this particular transom I did not follow the conventional rules of engagement. Used my own secret sauce method. I'll have to see how it turns out in year 2040 and then report back to ya.

The pretty wood ones go bad too. I replaced mine a couple years ago. But with my Thompson I was able to build it stronger than the original and it still looked good. With our "woodys" I think we are able to see the problem sooner, not waiting until the transom starts flexing and giving way in order to tell (like your nephew, Cal!!) . Not that I am complaining!!! That Merc looks pretty sweet on my Thompson.
Bill

With alternatives to wood, any kind of wood, available today, it seems to me to be crazy to use wood in a new transom.

Poured resin with fiberglass or ceramic composite is the way to go. Use SeaCast or Carbon-Core CarbonBond. with one of those, it will last a lot longer than the person who owns the boat will. More solid, weighs a bit more, but pretty indestructible.

I wonder if that is why my grandpa would treat the wood of his home built boats back in the 30s and 40s with linseed oil thinned with turpentine. Dad said he would keep coating it as long as it would drink it in and then brush off any sitting residue when it would accept no more. Then it was coats of varnish. The oil kept any scratched areas for drinking water because it was already oil saturated. I wonder if the new epoxy would stick to wood that was treated like that without delaminating? I just may have to try an experiment on some marine plywood scraps.

With alternatives to wood, any kind of wood, available today, it seems to me to be crazy to use wood in a new transom.

Poured resin with fiberglass or ceramic composite is the way to go. Use SeaCast or Carbon-Core CarbonBond. with one of those, it will last a lot longer than the person who owns the boat will. More solid, weighs a bit more, but pretty indestructible.[/quote]

Some transom designs just do not permit a poured composite. This StarCraft does (did) not have a sandwich style where something could be poured into. It was just two layers of 3/4" plywood with a glass mat between the two. That was resined(?) to the 1/4" outside skin with nothing but a thin single layer of mat on the inboard side. This was glued to the motor well where it added extra support. If it wasn't for that motor well design and support the transom probably would have had catastrophic failure years ago.
I did not want to cut up the motor well and there are no other ways of installing a new fully laminated transom without completely removing the entire stern. My solution was to use two 2x12 treated that could be manipulated into position from the inside. A solid layer of outside construction adhesive was spread on, the kind used to glue landscape blocks in place and then the boards were positioned and held in place for three days with screws and fender washers. After that step was complete the cosmetic outside skin was just glued in place with the same adhesive and faired. The inside was backed by two gussets which are screwed and glued. The inside edges of the 2x12s were tabbed to the hull with 3 layers of glass mat. After tabbing the edges to the hull the 'open' boards were soaked with Thompsons water seal so the boards are essentially open to breath and dry out if they get wet.
The transom is now solid as a rock, no flex, breathable, and the motor does not bounce when the t/t is used. If it lasts ten years or more I won't GAS.

Seacast worked great for me. Made new inner and outer 1708 skins and then filled with the composite. Did the stringers as well. some pics below and video link here www.dropbox.com/s/6kmvby4jew1ktp3/L%20%26%20S%20Part%20I.mp4?dl=0 seacast pour is about half way through and some other videos here lakenseaorg.wordpress.com/

Beautiful work! Curious how you extended your transom for the long shaft.

I bought some aluminum from metals on line, they will cut to size. marked it up and had a local welder stitch it together for me. then hit it with the polishing wheel so it blends in the repro transom protector I had already made under it. you can buy ready made transom risers but this one needed a little extra width for the new seacast transom and slots for the merc thumb screws. yes, it's probably overbuilt...

I had my rebuilt from 15 " to 20 " years ago came out beautiful

Looks professional to me. Beautiful.

Looks like excellent work to me but how exactly are you guys fastening to the interior bulkheads? Are you just laying FG mat in the corners? It looks to me like the whole nine yards could be snatched away straight out the back. I think I'd sandwich the new transom to the hull sides with 5200 and secure in place with a couple dozen counter-sunk stainless steel 3" screws all around, then fill the screw holes with epoxy. Just curious.

Oh...I'd would also have used white oak in place of treated Douglas Fir...but that just me.

AND...I would have sealed with CPES. Thompson's Water Seal is junk: Just a bunch of parafin wax in suspension. I built/rebuilt/pressure washed custom decks and docks for 20+ years and have seen the "protection" it provided.

Trying not to be a PITA.

Though this isn’t a transom replacement video, it is an interesting video on using Coosa board from Andy at Boatworkstoday.com. I have seen a few videos of using the Coosa board for transom replacement. I think one was from a new fishing boat manufacturer and the other I saw was from that Ship Shape video. I will have to look for that. Regardless of methods, it looks like everyone is doing their best work and with safety in mind. Nobody wants a rotted transom failure.

No PITA at all. You know what they way about opinions. They're like a--holes, everybody's got one.
The transoms I've rebuilt have all had the outer skin left intact so there's no compromise of the outside integrity and strength, 'ecept this last one. Just couldn't get to the doggone thing from inside. That being said on the StarCraft I did leave14" of outer skin on each side that is part of the hull. Those old pine boards are run to the edges of the hull and then the glass is tabbed to the sides and deck then gussets are place from the transom to the deck. Gotta remember that the upper board is also glued and through bolted to the motor well which was not disturbed. If I would have cut that i'de been screwed. When everything was set and dry the section of outer skin was attached and that is also through bolted with the motor mounts.
5200 and CPES would be much much better, I've used both of them before when I replaced the white oak frames and African mahogany bottom of my Century. But funds play a part in this project. Besides....I carry life jackets
I did baptize it yesterday to shake down the eggbeater. Did find some issues....Vibration and the doggone key kept falling out of the ignition.