TOPIC: The dreaded, "What do I use for transom wood?"

I almost have the portion of the transom which is to be replaced out. If it hadn't been for the embedded 3/8" tee nuts (Which are 4-ounce chunks of steel with a 1-1/8" hex end on them), I would have been done with this long ago.

Now the question is, what should I use for wood. After measuring the maximum transom thickness over which my motor mount brackets will fit and subtracting the thickness of the existing fiberglass skin, I come up with a core thickness of 1.955", just .050" short of two inches.

I have not removed the cap, so I will be inserting the wood through the top slot, which does not extend all the way across the boat. For this reason, I have considered several ways of splicing the wood - all of which will work, according to my experience in building wooden aircraft which cruise quite a bit faster than this boat will ever go and have higher loads.

That being said, one of the ways I am chewing over is to make the new core from horizontal White Oak planks, inserting them one at a time.

Anyone have experience with using this method? I think it wood (pun intended) be superior to plywood.

Clark,

I just happen to be working on a transom replacement today. I'm having a lunch break. I don't know what boat you are working on, but the best way to replace a transom is from the inside of the boat. This usually means pulling the deck from he hull, which can be pretty intimidating of a job. That allows full access to the rotted core for removal & replacement. Partial replacement will not be as strong or long lasting of a repair. MDO exterior grade signboard is the best wood for the money. Doug Fir with very few voids, phenolic resins. Good & very strong. I advise against the oak planks, plywood is more stable in this application.

Good luck.

I do NOT think individual planks of White Oak is a good idea for a Transom. There would be WAY to much flex. The transom needs to be ONE SOLID CORE piece and should be tabbed to the sides of the hull in most cases. If you do not want to go to the trouble of removing the deck and removing the inner skin in order to replace the transom in one piece, you might consider POURING a SeaCast or NidaBond transom. Google it up. Very STRONG composite material but a bit PRICEY. Lots of examples of this method on iBoats.com.

I used seacast on our ski boat YEARS ago, the rest of the hull is pretty well shot but the transom is still rock solid.

As was said the core should be one piece and should be plywood. The plywood should be nothing less than a good exterior grade but marine grade is better. As was said sign board is excellent. We used to use it for navigation day marks, and we completely sealed it. The ply should be completely coated in epoxy resin to seal all ends and edges before you put it in. If you drill any holes in it after it is installed they should also be sealed with epoxy resin. You are trying to prevent any water from entering the wood core and stabilizing the wood so it doesn't expand and contract from variations in moisture.

Bruce Gerard wrote:

Clark,

I just happen to be working on a transom replacement today. I'm having a lunch break. I don't know what boat you are working on, but the best way to replace a transom is from the inside of the boat. This usually means pulling the deck from he hull, which can be pretty intimidating of a job. That allows full access to the rotted core for removal & replacement. Partial replacement will not be as strong or long lasting of a repair. MDO exterior grade signboard is the best wood for the money. Doug Fir with very few voids, phenolic resins. Good & very strong. I advise against the oak planks, plywood is more stable in this application.

Good luck.

Well Bruce, I rely on skill a lot more than luck. And, take my word for it (as a semi-expert woodworker) I am not doing anything quick and dirty. If I thought my repairs the way I am proceeding were not adequate, I would be doing something different.

At one time I built, owned and finally sold a fiberglass manufacturing company, so I am also somewhat familiar with that product. I guess my idea for the White Oak planks comes from watching too many of Norm's woodworking shows on PBS!

However, I am a bit intrigued with your idea of MDO. Other than using it to build stable worktables, I had not thought of using it in a structural application. Some research on my part is called for to ponder it's use for this. Possibly making some sample glue joints and testing them to destruction.

Thanks for the idea.

Hi Clark,
For my transoms I used two layers of 3/4-inch AB-grade exterior plywood. Bedded the first layer to the skin with thickened epoxy, clamped and screwed (temporarily) in place. Then bedded the second layer to the first the same way. I also used a layer of glass cloth between plywood layers to act as a wick for the epoxy. I then glassed over the whole works, tabbing it into the chines and bottom with 8-10 inch overlaps. You could drive a ship into the transom of mine and the ship would come away the worse for it!

- Scott

Gee, I might as well join in here. I usually stay out of these discussions, because I am a proponent of marine plywood. It's pricey, so most folks don't want to spend the dough. To me, the price issue is ridiculous, given the amount of $ going into any boat restoration. I like marine plywood for a couple reasons - #1 it's made for marine use, #2, there are always more laminations per inch than any other kind of plywood, and #3, there are no voids or gaps between layers. Each to their own.

Frank

Frank, etc. . . .

Talk about pricey! When I built my plane, I used Finnish Birch plywood, which is totally waterproof, "A" on both sides, zero voids, and a 1/4" thick piece (actually 6 mm) has about 9 layers.

The only problem with it is that it is available in 5' square sheets. So, anything over 5', you have to splice it. I got pretty good at making scarf joints that were stronger than a continuous piece. Test samples would break somewhere else than the scarf joint.

I don't think this transom deserves 4 pieces of $100 plywood. I will likely use some A/C exterior. Should be able to get the entire transom out of one 4'x8' sheet. After considering the matter, I am inclined to jigsaw the outboard well from each end of the exposed center top of the transom.

I would need to cut about a foot each way to the gunnel, then split the joint. It shouldn't be too hard to repair and that will give me full access to the top of the transom. Then I can assemble a laminated transom and slip it down in from the top. I have removed almost all of the old wood now and was even able to save the old tabbing.

The windshield guy was here today and we removed the broken windshield on the port side to make a new one. I had to cut one of the corner "L" braces with a hacksaw as it would not budge out of the Aluminum frame. At first I thought they had used Stainless because of the way it was cutting. Then I saw the shaving and realized they had used an "L" shaped piece of Brass! Before I get the new glass, my job is to remove the two pieces of the brace from the edging and Silver solder them back together. I could cut a new piece out of sheet Aluminum, I suppose but since Boeing Surplus went out of business, my favorite source of Aluminum has disappeared.