20 Transom Rebuild

EP · #1 03-17-2003, 03:34 PM

I am in the process of replacing my transom. My project is the same as hammer's 20 on the picture section. I have cut all the old transom out, replaced the core with new marine grade plywood that is glued and screwed into place, and i have attached the outer skin. I am ready to glass the seam but.. I am worried about the strength of that seam considering the wood and fiberglass skin were cut in the same place. Is the lay up of glass enough to have confidence that this transom is strong enough for my new 150? (my cut out is the exact same as hammer's) I have thought of two options to make it stronger: 1) Drill through the top of the transom down 10 inches and insert a stainless rod to connect the old plywood to the new. 2) Make a stainless backing plate on the inside liner to hold the new transom in. ( the not so clever solution or desirable) So here is what i have thought of What are your opinions and experiences? Thanks Eric

SECF3114M73J · #2 03-17-2003, 04:09 PM

A freind just finished the transom on his 23. He added 2 knees or gussetts on each side about a foot off the centerline. The transom is like a rock.

Briguy · #3 03-18-2003, 04:56 PM

I did the same thing. I was confident my fiberglass work of 3 layers on the outside and inside was strong enough. A fiberglass expert looked at my project and recommended that I fabricate some knees connecting the stringers to the transom. You can see a picture here.

http://www.theboatzone.com/gallery/briguy/briguy21

I used corecell and a biaxel/matt cloth. Its really strong now.

EP · #4 03-19-2003, 11:50 PM

I ran four 12" 5/16 rods down through the top of the transom to connect the old ply to the new ply below it. I am ready to glass the seam. Do you guys think I have taken all the precautions to make it as strong as I can? Other than giving it the old "tire kick" for the solidness any other ideas to put some cinfidence in my mind?

EBEACH · #5 03-20-2003, 09:10 AM

EP, The only other way I could think to tie the two cores together would be to use a router with a 1/2" or 3/4” straight cutting bit, and plunge down into one section and across the seam into the other, then use wood or fiberglass to create a biscuit joint. What was the condition of the wood on the periphery?

EP · #6 03-20-2003, 09:22 AM

On the sides and top I cut back to were there wasn't any rot but on the bottom by the drain plug it was rotted all the way. I dug what was rotted there and filled with epoxy. The rods have created that biscuit joint.

EP · #7 03-20-2003, 08:09 PM

Used alot of West System today and am very confident in my work that it is as strong as new. Thanks

EP · #8 03-21-2003, 10:44 PM

I have come to the conclusion that I am not going to use cloth in over the seam but use more west system to fair out what I have ground out. If anyone with good knowledge about this project would give me advice it would be great. I don't see how the cloth would add much strength to it as I have now filled the gap between the existing skin and cut off skin mending them back together. I am also taking into consideration the work it would take if I built up cloth then started fairing. I have seen it done with out the cloth but am just asking peoples opinion to make sure it is the right way to go. Sorry about my constant questions but I would rather ask first. Thanks Guys... Pictures to come

EBEACH · #9 03-21-2003, 11:22 PM

EP, First off, let me say that I'm no expert, but I will try to offer some advice on what I've learned and researched.

Your seam should be tapered back from the cut line at about a ratio of 10-12 to 1. That is to say if the fiberglass that you're repairing is 1/4" thick, you should grind the glass outward from the cut line 3" (12 x 1/4 = 3") on a taper. You must use fiberglass for the repair. It is the glass that is giving you strength, not the resin. Too much resin can be a bad thing.

It's also best if you can do your lay-up in one shot, if attaching fiberglass to fiberglass. Once the resin has passed it's peak "exotherm" state, any bonding thereafter is mechanical and not chemical.