Transom wood question

[Asche]

Not had luck with searches. I am working on replacing the transom wood in a 1990 14' Altra. The wood will be between the hull and a second metal panel. It only holds a 15 hp Evinrude.

I have two questions on the matter:
The first being, if the wood will be sandwiched between the two metal layers, is it necessary to use an epoxy or any sort of glue to adhere two boards together to make up the thickness, or can they just be placed in and run all the bolts through to hold it all together?

The second is, are there any sorts of plywood that are more effective, or terms that will actually provide results? When I ask locally for marine or exterior grade plywood that isn't pressure treated, I get either a deer in the headlights stare, or looked at as if I just sprouted 12 arms from my skull; or they just direct me to pressure treated anyway. Or would a couple of oak boards be sufficient to handle the motor?

This is what was left of what I assume was regular plywood.

 

[LDUBS]

Not had luck with searches. I am working on replacing the transom wood in a 1990 14' Altra. The wood will be between the hull and a second metal panel. It only holds a 15 hp Evinrude.

I have two questions on the matter:
The first being, if the wood will be sandwiched between the two metal layers, is it necessary to use an epoxy or any sort of glue to adhere two boards together to make up the thickness, or can they just be placed in and run all the bolts through to hold it all together?

Welcome to Tin Boats.net

I would glue the two thicknesses together. Titebond III waterproof glue is likely the most economical. Epoxy would be considered a structural adhesive. In my opinion epoxy is not needed for this, unless you happen to have it on hand.

When I laminate things, I glue them together before cutting to final size. I just find it easier.

The second is, are there any sorts of plywood that are more effective, or terms that will actually provide results? When I ask locally for marine or exterior grade plywood that isn't pressure treated, I get either a deer in the headlights stare, or looked at as if I just sprouted 12 arms from my skull; or they just direct me to pressure treated anyway. Or would a couple of oak boards be sufficient to handle the motor?

Ask for CDX plywood. Marine grade is a specialty plywood. In my experience, it is not commonly stocked by your neighborhood lumberyard/big box store. Marine grade would be the ultimate choice with a high price. Both marine grade and exterior grade use waterproof glue. Exterior grade will have some voids in the laminations. Marine grade doesn't have voids in the laminations. Both should be sealed. I side with many here who would use exterior CDX as opposed to higher cost marine grade.

Oak boards would be a great choice too. If available, opt for white oak.

Whatever you use, it is a good idea to seal it up prior to installation.

 

[lckstckn2smknbrls]

BCX plywood will work too. The X means its exterior grade.

 

[FuzzyGrub]

Welcome to Tin Boats.net

I would glue the two thicknesses together. Titebond III waterproof glue is likely the most economical. Epoxy would be considered a structural adhesive. In my opinion epoxy is not needed for this, unless you happen to have it on hand.

When I laminate things, I glue them together before cutting to final size. I just find it easier.



Ask for CDX plywood. Marine grade is a specialty plywood. In my experience, it is not commonly stocked by your neighborhood lumberyard/big box store. Marine grade would be the ultimate choice with a high price. Both marine grade and exterior grade use waterproof glue. Exterior grade will have some voids in the laminations. Marine grade doesn't have voids in the laminations. Both should be sealed. I side with many here who would use exterior CDX as opposed to higher cost marine grade.

Oak boards would be a great choice too. If available, opt for white oak.

Whatever you use, it is a good idea to seal it up prior to installation.

I agree, except for the oak. I used red oak on a transom and did not hold up. Warped badly and splits along grain. It did look good for the first couple of years. Plywood is the right choice.

 

[mbullen]

White Oak, Mahogany, and/or Marine Ply are the usual suspects for transom construction.
One can step up or down from that set with the more expensive Coosa Blueboard or the less expensive Exterior Ply.

For what it's worth, Red Oak is not recommended for boat building as it has a cellular structure that puts it at a disadvantage in a marine environment.

 

[Asche]

BCX plywood will work too. The X means its exterior grade.

Would it matter the sort of wood if it's BCX plywood? Only one I can find locally is southern yellow pine.

 

[Asche]

White Oak, Mahogany, and/or Marine Ply are the usual suspects for transom construction.
One can step up or down from that set with the more expensive Coosa Blueboard or the less expensive Exterior Ply.

For what it's worth, Red Oak is not recommended for boat building as it has a cellular structure that puts it at a disadvantage in a marine environment.

If I go with oak, I'd be going to an amish sawmill, and getting some white oak that's cut to the correct thickness. Plenty of that around. Just been a struggle with plywood sources here.

I miss having more options than Lowe's and Home Depot for such things.

 

[lckstckn2smknbrls]

Would it matter the sort of wood if it's BCX plywood? Only one I can find locally is southern yellow pine.

SYP X grade would be a good choice.

 

[airshot]

Oak boards will work but you need two or more that need to be glued together to give lateral strength so they don't split and warp. In other words use some thinner pieces and glue them together to get the needed thickness as it will make a much stronger board.

 

[lckstckn2smknbrls]

SYP X grade would be a good choice.

Don't forget to seal the wood.

 

[Asche]

Don't forget to seal the wood.

Already planned that. I have some Helmsman spar urethane I use on paddles and oars. Planning to give it 3 or 4 coats of that before installing.

Probably going to toss some clear silicon around all the bolt and screw holes, and on the washers before reinstalling them just for added protection.

 

[LDUBS]

Aw, there is always something it seems. There are many reports that the acetic acid in typical kitchen/bath silicon can etch aluminum and potentially lead to corrosion. The general consensus is to make sure the label on whatever you use says it plays nice with aluminum.

BTW, being able to get white oak milled to thickness is awesome. Whatever material you decide to use, sealing it will give it a much longer life.

 

[MattA]

Look at baltic birtch its has no voids in it like normal ply wood.I found a place in Arizona I ordered my wood from and you can get it pre cut. Just needs to be sanded and sealed. I'm going to replace my transom this winter and that's what I'm planning to order.
https://www.woodworkerssource.com/plywood-sheet-goods/baltic-birch-plywood.html

 

[aldabob]

I'm doing my transom on a 1987 Smokercraft, I bought Marine plywood. Philippine Mahogany and its 12 ply. You get what you pay for and it's not cheap 180 sheet.