Transom replacement - solid wood or plywood

[WisRob]

I am replacing the transom on a 1969 Polarcraft aluminum jon boat. The original wood is 1 1/4 thick plywood. It is 12 inches tall and 63 inches wide at the widest. Everything that I read says to glue together 3/4 marine grade plywood. If I go with plywood, I will need two full sheets, 1/2 inch and 3/4, to get to 1 1/4. Is there any reason why I can't use a solid piece of 5/4 lumber? If so, what kind of wood?

 

[GTS225]

Well, I suggest you're going to have difficulty finding a true, 12 inch wide piece of lumber, as dimensional 2x12's will actually measure about 11.5". If you can find it though, make it Cedar or Redwood. Both of those have decent resistance to rot, and you can paint it to seal it up for additional protection. You do risk warpage from a solid piece, though, where plywoods have much less risk.

I can tell you this, though. DO NOT use pressure treated woods of any variety. The chemicals tend to react with aluminum, causing quite damaging corrosion, even to the point of pin-holing your hull.

Roger

 

[WisRob]

It looks like they sell 5/8 marine plywood, so I could get 1 1/4 by combining two pieces of 5/8 plywood. The 5/8 is actually .563, so 2 of them added up to 1.126. That is .124 less than 1.25. Does then epoxy add up to .124?

 

[DaleH]

Exterior ply uses the same glue, but voids are not filled. If you treat the wood with epoxy from www.raka.com, you won't need to worry about voids. I also once did a transom using 1-piece of ply by laying it out 'on an angle' on a sheet.

Most hull layouts can accommodate a somewhat thinner transom, so I don't foresee any issues, but do not know your rig of course.

Some good info here on epoxying wood and through-hull penetrations: https://forum.tinboats.net/viewtopic.php?f=3&t=47405

 

[lckstckn2smknbrls]

Plywood is less likely to crack / check due the the grain of each ply running in different directions. White oak would be my choice if doing solid wood. I like Old timers formula for sealing wood.

 

[Budlum]

It looks like they sell 5/8 marine plywood, so I could get 1 1/4 by combining two pieces of 5/8 plywood. The 5/8 is actually .563, so 2 of them added up to 1.126. That is .124 less than 1.25. Does then epoxy add up to .I would only use the marine plywood if you need to add wood to a transom and you can put a sheet of 1/8 aluminum if needed. That’s only .001 interference, easy to fit in and tight. At least big enough to attach the motor on it will give you good long service.

 

[Budlum]

I would use the marine plywood and a sheet of .125 aluminum. A tight fit but that’s what you want. At least enough to make a good surface to mount your outboard. Attach it with 1/2” wood screws or anything handy.

 

[Colorado1135]

Don't worry about marine grade. I used wood glue between the two sheets I used and then put in multiple screws and then put a bunch of weights on mine when I did it. Once it dries I pulled out the screws then put a layer of epoxy resin and fiberglass on the exterior surfaces. Slipped right in and is impervious to water. On your through hull fittings remember to coat with something to seal and keep the water out of the holes

 

[Sieben]

You could use coosa board. It is designed for just things like a transom replacement. It comes in different thicknesses. It can be glued in layers with West System Epoxy. impervious to rot, stronger that plywood.

 

[gps4]

You could use coosa board. It is designed for just things like a transom replacement. It comes in different thicknesses. It can be glued in layers with West System Epoxy. impervious to rot, stronger that plywood.

is there anywhere to get coosa board without havign to order a whole sheet? i need a piece about 1" thick, 12" wide and 5" long.

 

[Sieben]

Google search. Various sizes.