TOPIC: Gap under transom?

I am getting back to the Glastron project and started to cut out the glass on the inside to remove the rotted transom. When I cut the bottom part, I discovered that there is a 1/2" to 3/4" gap between the bottom of the transom plywood and the fiberglass hull. I assume that this is a construction error and that the plywood should be tight to the bottom of the hull. My thought is to make an epoxy mix with lime of some filler to fill any gaps with the new wood. I should be able to get closer than 3/4". Has anyone else run into this before?

Hard to believe that the factory turned out something like that Todd, but I guess that may have been built back in the beginning of their "learning curve"?! Any evidence that someone else (P.O.) has "rebuilt" the transom in the past? Whoever did it, they sure didn't help the strength of the transom doing it that way.

PS - I love my Glastrons, but they did have some questionable building practices in the early years through the 70's that I know of. Poor drainage (under floor and bilge), untreated (unsealed is what I mean) plywood bulkheads, etc... Great designs though, it's just up to us to bring them "up to par".

Not being able to see how badly rotted the old plywood is it is hard to say. But rotting wood sometimes swells up and I've seen it sort of shrink too. I'll bet a stack of quarters you can do better.

It appears that this is the original transom. Either that is was a great matching fiberglass job over a crappy plywood job. The only rot appears to be around penetrations, so I doubt this is shrinkage. There doesn't seem to be any additional rot around the bottom so my guess is that the fiberglass was tight. Robert, you are right, I will do a little better job than this one.

Today's search is for 3/4" marine plywood. Hopefully I can get the old one out this weekend

MarkS wrote:

Hard to believe that the factory turned out something like that Todd, but I guess that may have been built back in the beginning of their "learning curve"?!

If you dig in to enough boats, you will find a LOT of stuff like that from the factory- You would be amazed what is done in areas that are sealed off, never to be seen (under usual circumstances!). I've worked on a number of Glasspars, and the level of build quality varies considerably from boat to boat- Even on similar boats built at the same plant in the same year. I'd imagine some were friday boats, some were monday boats, and some the supervisor just wasn't looking. It's probably the same for other manufacturers, too.

The gap PROBABLY should have been filled with a resin mixture when it was built. I'd assume you are just replacing all the plywood with new, so when you do, just use enough of whatever thickened resin mixture you are using to bed the plywood so it 'squeezes' out to fill the area. This also keeps you from having to be exact with the plywood cutout- You just need to be close, and it will work out fine.

I use Aerosil/Cabosil with epoxy for most jobs like that. Works quite well.

-Andrew

+1 on this ^^^^. Thickened Resin will fill that gap quite nicely and make for a nice strong structure. That must have been a "Friday Afternoon" build when the boys were in a hurry to get to the bar!!!!

I think I figured out why they did this. On either end, the transom piece extends part way up the fins, to the bottom of the cap piece. The total distance from the bottom of the hull to the bottom of the cap piece is just shy of 25". My guess is that one of two things happened: Either the cap piece was cut an inch short or the transom was measured from the top down and the overall was never considered (or both). My assumption is that they used a 1/2 sheet of plywood, so they only had 24" to work with, hence, the gap.

My solution for this is to leave a 1-1/2" protrusion into the fin space on the back piece of plywood. (The transom is two pieces of 3/4" plywood glued together.) This will create a lip where I can build the fin piece to the correct size and attach it to the transom with a scarf joint. With enough epoxy, SS screws and fiberglass to cover, it should be a solid.