Transom Ply Question

[Mojo^]

It's been some time since I've had a chance to work on my Jon but when I tried to install the new transom core yesterday, it wouldn't fit. The old core looked to be two layers of 3/4 ply merely tacked together with staples and not sealed. I made a new core using two layers of 3/4" exterior ply bonded together with PL and coated with medium 635 epoxy resin from U.S. Composites. The core is sandwiched between aluminum structure. I had a new piece of aluminum welded onto the exterior side of the transom (old one was badly corroded) and I'm thinking that there may be some distortion. I've tried beveling the edges of the new core but that didn't seem to help much. The new core seems to be too thick to allow the inner aluminum structure to fit-up properly causing the rivet holes on the sides to misalign, so much so that I can't even get a cleco in them. So, it looks like I need to fab another transom core. Would there be any problem with using two layers of ply of differing thickness? I was thinking one layer of 3/4" and the other layer being 1/2". I don't much care for the idea but I'm at a loss at what else I can do to reinstall the core.

 

[Star]

Re: Transom Ply Question

The materials that you glued and coated your new transom have some thickness. Did oyuclamp it well when you put it together. I bought a 1961 a 14' alum that spent most of it's life outside. Original seats amd transom. 10 years later I redid the transom with 3/4" marine ply, $75 on sale I sealed the top
with a vineer and glued it with Epoxy. Top coated it with 3 coats of varnish it will still be here when I die for sure. The original transom plate was still intact with minor rot after 49 years just varnished. Take a belt sander with 50 grit and grind it down till it fits, then reseal it!

 

[njdrt-rdr]

Re: Transom Ply Question

I'm not sure if it's a good idea or not, but I'm doing the same thing as you. My transom original piece is like 1 1/8 thick, I think I'm using a 3/4 piece and a 3/8 piece together. Then I was going to epoxy the thing. Was just coming on iboats to search what kind of epoxy to use. I'm taking a ride to west marine tonight and want to get the right stuff.

I would think as long as glued together well, it wouldn't make a difference if you used 2 different sizes of plywood.

 

[Mojo^]

Re: Transom Ply Question

I used a notched trowel to apply the PL and clamped it for three days while it cured so I don't think I have too much adhesive between the layers. The epoxy added a little to the thickness, but not that much. The new core seems to be about 1/4" too thick now and I'm just not comfortable trying to sand away that material much on plywood. Maybe it is a build-up of epoxy and adhesive afterall. I guess I'll give the 3/4 + 1/2 ply a try and see what happens.

 

[ondarvr]

Re: Transom Ply Question

It makes no difference in how you get to the correct thickness, just so the total thickness is correct. Sheets of plywood are rarely exactly the same thickness, so just using two new 3/4 sheets doesn't mean it will be the same thickness as two 30 year old sheets.