Interior Refurbishing

Transom III

The new transom, with symmetrical cut-out and holes drilled for motor mount.

Since the last post I bonded layers 3 and 4 to the transom! The 3^rd was ¼”, and just slid in behind the shoulder at the aftermost part of the center rib with a gap a bit less than ⅛”.

The third ply in place. I later thoroughly filled the gap with GelMagic.

The 4^th and last was the ½“ thick plywood, which I cut out to accommodate the knee. I took special care to shape the edges so they fit flush to the curvature of the hull. For this I used a grinder with a 60-grit flapper wheel; it's easy to control and and quickly removes material.

Shaping the edge of the last ply.

To measure the amount of material to grind off I used a straight edge on a scrap of the appropriate size plywood, and measured the distance between the previous ply and the hull every three vertical inches. With the previous ply template laid on the plywood to be cut, I just added these measurements to the ends (the pencil line to the left of the grinder above is a trace of the template). This is another thing best explained with a picture.

Measuring the taper for the fourth (and last) ply.

Final ply in place with the usual liberal coat of GelMagic between it and the previous layer, and bent in place with prop sticks. 

I “cooked” if for three days at about 80°so the epoxy is well cured, then got on with reinforcing the whole thing. For that I used an interesting material called “double bias w/mat.” It is 25.3 oz/yd², which is by far the heaviest cloth I’ve ever used, and will add even more strength to the transom.

Both sides of the transom reinforcement mat.

It comes in 8” wide rolls and is very easy to handle. I applied this in two layers, the first horizontal and the second vertical. If it wasn't double bias I would have laid the second layer at a 45° angle, which would generate significant waste. I just butted the joints together to make a smooth surface. As you can imagine, this material really sucks up the epoxy! I used about a quart for each layer. To lay the first layer I brushed resin on the plywood transom then just stuck the cloth on that, liberally applied resin and squeegeed it in, then worked out any bubbles with the squeegee. For the second layer I cut the strips, wetted them out on a table, then set them in place and carefully squeegeed them. It turned out so nice I may not lay finishing cloth on this surface. A coat or two of resin should make the fibers disappear and I can prime and paint right over it.

Panaorama of the fiberglass reinforcing.

The remaining tasks were to reinforce the transom-shoulder joint, buttress the transom with longitudinal members, and finish off the top of the transom. I'll save the latter for later (!), since I need to do a bit of surgery to the center cutout for proper vertical alignment of the engine.

Reinforcement of transom-shoulder joint.

Even though the transom seems very sturdy, I emulated Bruce B's idea of adding longitudinal supports. For these I cast the 25.3 oz mat around a 2 X 4 mold (true dimensions were 1½ X 3, with ½" routed edges). I added to this for a total of 2 layers of fabric. Very strong and light (8 oz/linear foot), these will distribute thrust to the aft bulkhead. So, if the next owner feels the need to hang a 150 hp motor on the stern the transom probably won't splinter.

Completed beam.

Cut section of longitudinal support.

I bonded them in place with GelMagic, after roughing up the old fiberglass and cleaning it with acetone. Bruce added fiberglass mat to better tie the ends into the transom and bulkhead, but I elected not to do that. A small fillet of GelMagic satisfied me that everything will remain in place when stressed.

Supports in place. 

I'm currently working on installing the splash shelf. You will note on the above photo that I've already installed a cleat on the bulkhead to support the shelf.