Step 4: Install new plywood core

Installing the new core: your new plywood core should be the same total thickness as the original plywood. If you are changing anything about the design of the transom (higher engine mounts, enclosed transom, bracket, etc...) you may need to make adjustments to the thickness of the core. Post details on the forum and we can help with this. Most powerboat transoms are made by laminating multiple layers of 1/2" or 3/4" plywood. It is not a problem to make a very thick transom by using epoxy to laminate many layers together, in fact it is quite the opposite.

Plywood selection is another topic covered in other tutorials, please read this for more information

The new core can be either made in one piece, then bonded into the hull, or you may laminate one layer at a time into the hull. It is generally easier to laminate the core outside the boat and bond it into the hull once, but on very large transoms this may not be possible due to weight and difficultly in handling.

To laminate two pieces of plywood, first coat the faces of the plywood that will be glued together with un-thickened (neat) epoxy resin. This is a thin coat of epoxy, just enough to let the face of the wood soak up a little epoxy. While this epoxy is wet, mix a batch of epoxy glue. Epoxy glue is made from same epoxy with wood flour mixed in to reach a "ketchup" consistency . Using a notched spreader, apply even amounts of epoxy glue to each plywood face. Now clamp the two layers together using weights, clamps, or dry wall screws (temporary, removed after glue cures). Do not apply too much pressure! Epoxy is gap filling and extremely strong, you want the epoxy to remain between the plywood layers. Once the epoxy begins to squeeze out the sides evenly it is time to stop the clamping pressure

We have videos and tutorials on mixing epoxy and making epoxy glue here.

In the example boat the customer decided to laminate each layer one by one into the hull. The method is the same as if the laminations were made outside the boat: apply epoxy, then glue, then clamp.

In picture 1 you can see the first layer clamped into place (plywood is Meranti BS1088).

After 3 layers total, we have the total core thickness epoxied into place. (picture 2)

<p>I recently rebuilt the transom of my 1965 Gold Cup runabout. The plywood was so rotten I was able to tear most of it out with my bear hands and it was so wet that I was able to wring water out of it. Overall, the project cost less to complete than I had thought but was a great deal more work. </p>
Sounds just like me. I replaced one in my 1966 starcraft 18 foot. Yep lots of work. Did you haft to glue too pieces of marine plywood together too.
<p>I have a 89 Tracker 1800 TF. The previous owner had motor toter fail while trailering. That allowed the outboard to bounce and it slid down to the top of the slots on the bottom bolts and the top bolts &quot;wallered out&quot; the holes through the transom. I was thinking about injecting some Git-Rot around all the bolt holes to seal up the exposed wood. Then I was going to epoxy some 1/2&quot; inserts into the bad upper holes with Marine-Tex/ then seal all the bolt holes with a good marine sealant before reinstalling the outboard. Finally I got an aluminum transom brace to go between the top bolts. Anyone have any thoughts on this?</p>
<p>Hi there </p><p>I have a 4.4 meter sea master fibreglass boat. I found after replacing battery the transom was rotten all around the aux motor bracket, the two hooks on rear and rot around where the 70 hp motor bolts on. It was up to the stage of scrapping out mushy ply with a screwdriver. I think it all started because all the penetrations in the transom where directly through the ply, with no source of water proofing around the internal part of the hole. Even around the bungs!!! is this normal boat building???</p><p>My big question is' I decided to fix it my self and have so far cut all the rotten ply and more, out of the transom flush to the floor in the boat. All the ply that i can visibly see is in good condition. Can i solidly make a new transom to the shape of my floor, and dowel it into good timber. Then glass it all in from there?</p><p>Trying to avoid disruption the floor/stringers to cut out the last little piece of the transom.</p><p>Any one got any ideas or advice on this??</p><p>no images at this stage</p><p>Mark</p>
I did this to my old Fibercraft ob boat 15 years ago. It is thill holding up wery well. In all my pass through points for deck drains, I used Marine tex and pvc pipe to seal any possible points of water intrusion into the core. Before removing the old skin I copied the boat serial number that was molded into the fiberglass. When I was done I used a dremel to engrave the numers into the new skin. <br>I brushed on colored gel coat to match the original boat color. It wasn't perfect, but close.
I helped a friend do this once, it's a LOT of work !

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