The Transom Repair
(Getting the Rot Out!)

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Open Combing Side
I had the help of a local wooden boat restorer for the transom repair.

The first step was to separate the upper deck from the hull.  The rubrail and underrail were removed, as were the staples that held everything together.  The sides of the upper deck were propped up to give me access to the transom core.

(The under rail is hanging to the ground in these pictures.)

This is the aft view.  (Note the radio on the foredeck - very important tool!)

The next step was to peel back the fiberglass cloth on the interior of the transom.  On some of the later models, the seats run right up to the transom, which makes access to the core a bit more difficult.  I decided to keep the outer skin intact and maintain the integrity of the outer hull.

With the core exposed, I used a large putty knife to scrape out the old core.  A shop vac came in real handy during this process! 

Open Combing Aft
Rotted Transom Wide
This is what I found inside the transom -  the core had the consistancy of garden mulch about 2/3 of the way down.  At the bottom section, I used the putty knife to pry the plywood core off of the outer skin.  I left some of the original tabbing to the side hull intact until the end to try and retain a channel to put the new core into.

(Note that the seats end 8" from transom.)

This is a close up of the old soggy core.

The replacement core was to be three pieces of 1/4" AC plywood, laminated together with epoxy and silica (as a thickening agent), to give the full 3/4" thickness of the original core.  The reason for laminating thinner pieces together was to obtain the proper curvature of the stern.  Having the outer skin intact also helps to give you the original curve.

Rot CU
Old Core Groove
When the core was completely removed, I sanded the inside of the outer skin, and cut the old fiberglass cloth back, leaving a slight channel from the original core to fit the new core into.  This would help hold the pieces in place during the final lamination.

I cut a template from a large piece of cardboard, and kept trimming it until it fit into place.  I tried to fit it as close as possible, but any small gaps by the edges could later be filled in with the thickened epoxy.  There would also be 4" tabbing cloth glassed over the seams when everything was completed.

Dry Fit Core

Clamps Port

With the template cut, the pattern was transfered to the new plywood.  Each piece was custom-fit and numbered corresponding to it's position.  The pieces were all dry-fitted into position.  The old channel from the old core was utilized to hold the new pieces in position, leaving only the top to be clamped.

Each surface was coated with the thickened epoxy as it was put back into place.  I used purple plastic wrap (borrowed from the kitchen) to protect anything that might come into contact with the epoxy.  Epoxy won't stick to the plastic wrap, and the color makes it easier to see when everything is dry.  The clamps were placed to put even pressure along the top of the transom.

I rounded up every clamp I could find to set the core in place.  I used the old transom trim piece to transfer the curvature over to  2x4 laid on it's side.  I added a bit more curvature (for spring-back in the core), and cut the 2x4 with a jig saw.  The curved sections fit against the transom; this now gave me the outer flat sections for clamping surfaces (see picture below right).

Clamps Interior Clamps Top
Blocking Outside Clamps Back
The middle section of the core was screwed together with drywall screws driven through blocks on the interior & exterior (again using plastic wrap so the blocks won't bond to the core or exterior fiberglass).  This essentially  pulls the plywood pieces together, squeezing out any air pockets.  You can tap along the transom surface, and if you hear a different sound, this usually indicated an air pocket.
Blocking Interior
Interior Fairing
When everything was dry, I faired the seam where the core meets the hull with an epoxy and micro-balloon mixture.  This  gave a smooth, curved surface for the fiberglass cloth to bridge.

When the fairing material was dry, I once again sanded a smooth radius between the core and hull.

When all of the epoxy cured, I removed the clamps, screws, and blocks.  The screw holes were filled with epoxy (I used the fairing mixture).  Any rough spots were sanded prior to skinning the interior surface with fiberglass cloth.
I used the cardboard template to cut a heavy weight fiberglass cloth to size.  One piece of solid cloth is all that was needed to make a good, water tight skin over the plywood core.   When the cloth was in place, and the epoxy almost cured, I tabbed the cloth to the hull with 4" fiberglass tabbing cloth.  I made sure that all of the cloth was smooth, without any lumps, so final fairing would be easier.
Completed Transom
The final step will be to use the epoxy/micro-balloon fairing mixture to smooth the interior of the transom.  This makes the new transom blend into the hull where it can be painted to match the interior.  (It is probably better to time this repair with a new interior paint job!)

This section is for information ONLY!  I do not claim to be an expert, and I cannot be held liable for anybody else's repair job!  This is just a documentation of my repair.