Composite transom with failed plywood hardware pads

waterboy222

Seaman
Joined
Dec 5, 2011
Messages
56
I am rebuilding a late 90's Trojan (Carver) 400 Express. I pulled the trim tabs off last week to rebuild the cylinders and water poured out of the screw holes.. Yay...

I was under the impression, and according to Carver's literature, that there was no wood used below the water line on these boats. I guess they forgot about stringers and transom corners.

The transom is all glass except for the aft corners in the trim tab area. When you cut the fiberglass exterior skin off, you can find the plywood pad inside.

On the PORT side the wood was completely rotted and wet. The culprit here looks to be the screw holes for the trim tabs and the hole where the hydraulic line for the actuator comes through the transom. I dug/chipped/ground out all the wood and will be replacing it with marine grade 3/4 ply. It appeared that this whole area was done in one single sheet of plywood.


On the STBD side there was only one small area about a 1/2 wide that was wet. It was in a line directly below the hole for the hydraulic line. I removed about 10" wide of wood from the area and all the way to the bottom of the transom. The rest of the wood is bone dry. The black areas you see in the pictures is not wet, rot or mold, its simply the burn marks from the grinder and the dust from cutting through the black bottom paint. This area was done with three separate pieces of plywood with the gaps being filled with some type of foam. The glass had completely delaminated from the wood. If you zoom in, you can see a handful of glass fibers still stuck to the ply on the left side and some of the foam peeking out between the joints. The rest of fiberglass wasn't even touching the wood and there is no evidence of resin anywhere else. It looks like they laid the hull then after it cured they added the hardware pad without wetting it out then just glassed over the back of it.

My questions (finally). How should I repair this? Should I go ahead and remove all 3 pieces of ply from the starboard side and replace it with one panel? The joints in the material are simply butted together, they aren't scarfed at all. The filet material looks to be some kind of incredibly soft foam. I have dug almost all of it out. Should I go back with this same material or just use peanut butter?
I am adding 5 underwater lights across the transom and I don't want to worry about water intrusion again so I am considering making a 4x4 hole in the plywood and filling it with 1708/CSM until its the same thickness as the ply. That would give me a fiberglass area to screw the lights into and allow the wires to go through the transom without having any contact with wood. I plan on wetting out the marine grade ply, rolling on some slightly thickened epoxy onto the inside skin of the glass, attaching the new wood then drilling a hole through it so I can use a bolt/washer/nut to hold it all together while it cures then fill the bolt holes in.

Any advice is appreciated. I want to make sure I am on the right path before going to this next step.


http://imgur.com/QP3Kd7g
http://imgur.com/As2USXX
 
Last edited:

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,306
nearly all boats in the 90's used wood

I would have worked from the inside out, however you have gone this far.

if the area is simply a screw pad for the tabs, then I would make your life easy, remove the wood and build up layers of 1708 until you get flush with the outside, then fair, gel and bottom paint
this will give you a really thick chunk of GRP to screw into

if any of your foam is wet (high probability on a near 30 year old boat), then plan a gut and rebuild
 

Woodonglass

Supreme Mariner
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Dec 29, 2009
Messages
25,924
It'll take about 12 layers of 1708 to get the thickness you want I would use plywood and drill oversized holes filled with PB to prevent water intrusion
 

ondarvr

Supreme Mariner
Joined
Apr 6, 2005
Messages
11,527
If you don't want to worry about it again, use a sheet of Coosa Board in place of the plywood, it will last forever. A little more money, but not bad.

Any of the listed methods will work though.
 

waterboy222

Seaman
Joined
Dec 5, 2011
Messages
56
I would have worked from the inside out, however you have gone this far.

if the area is simply a screw pad for the tabs, then I would make your life easy, remove the wood and build up layers of 1708 until you get flush with the outside, then fair, gel and bottom paint
this will give you a really thick chunk of GRP to screw into

Going at this from the inside is a major task. That would involve engine hatch and furniture removal (requiring a crane), generator removal, Engine removal, exhaust removal, muffler floor removal, etc. So much easier to go at it from the outside.

As was said earlier, going with a full glass layup would require a lot of material to end up with almost 1" thick glass. I do like the idea of going with coosa board. It looks like you can work with it the same way as you would regular marine grade plywood and I wouldn't have to worry about leaking holes causing rot.

Also, I didnt plan on putting gelcoat back on the repair seeing how it will be under the bottom paint anyways. Is this a mistake? In the blister repair videos I've seen they say not to re-gel the repair since you will be putting bottom paint over it.
 
Last edited:

ondarvr

Supreme Mariner
Joined
Apr 6, 2005
Messages
11,527
It won't make a difference whether you use gel coat or not.
 

Roady68

Seaman Apprentice
Joined
Sep 17, 2016
Messages
38
If you don't want to worry about it again, use a sheet of Coosa Board in place of the plywood, it will last forever. A little more money, but not bad.

Any of the listed methods will work though.
I second it. I used Coosa for stringer repair. At some point, I will be into a transom repair and I will use Coosa there too.
 
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