Exterior vs interior plywood

[Drivewayboater2]

All, looking for advice on transom replacement materials. Since the wood will be sealed with resin and clothed over what’s the benefit of using exterior grade plywood vs interior grade for transom replacement? I see that the exterior is constructed with water proof glue. Any reason you can’t use interior if it’s completely sealed? Any advice is appreciated.

 

[Scott Danforth]

Because the $2cost savings per sheet isn't worth it

Because interior grade wood is has less plys

 

[Drivewayboater2]

Ah… gotcha. Thanks
i had some left over 3/4” BC hanging around. Just thought I’d could use it.

 

[jimmbo]

Wood is the Weak Link in Transom Longevity. Marine Grade Plywood is still Superior to Exterior Grade. Don't let anyone convince you they are the same, as they are not.

 

[kcassells]

Ah… gotcha. Thanks
i had some left over 3/4” BC hanging around. Just thought I’d could use it.

For marine you can use ACX,BCX and CDX. Acx being the wood with less voids consecutively etc. All use exterior grade glues. Marine is good if you can find it and pay the premium.
Myself, I 've never used marine.

 

[76SeaRay]

I tend to overkill so I used marine grade throughout my gut and build. I was just going to use it on the transom only but decided to go with it for stringers and floor after I got the transom in.... It was spendy though....

 

[kcassells]

That's Great! It is one of the first lines of defense. After that comes, prep, glassing and install.
The first doesn't matter if the follow thru isn't proper.

 

[froggy1150]

Fyi...
Plywood grades ab or c each side a being the best. And x designates exterior "waterproof glue"
So acx will have a good finish side, a crap side and waterproof glue. Bcx ok finish side, crap side and waterproof glue. I dont think they make abx. My marine grade was almost identical on each side. With marine grade they fill all the voids with those biscuits and I think it also has more plys

 

[tpenfield]

Why? Because, that's why

Actually, you want the plywood to have little/no chance of delaminating. Fiberglass/resin encapsulated wood does absorb moisture (water) over time and the higher levels of moisture could lead to ply separation.

 

[76SeaRay]

All plywood has voids on the inside as well as on the outside. As Froggy mentioned, marine grade has the external voids filled to finish the surface, however, marine grade also has a spec that limits the allowed internal layer voids. This means you have a much lower chance of a transom mounting bolt hitting a void when you drill through to mount the outdrive. As I mentioned, I used marine grade through out but, if I had to use other plywood for whatever reason, I would still use marine grade for the transom.

 

[kcassells]

Alrighty then .....

 

[jimmbo]

Alrighty then .....
View attachment 370191

Calgary Stampede? They beat horses, and other animals to Death, as part of Family Entertainment

 

[kcassells]

Calgary Stampede? They beat horses, and other animals to Death, as part of Family Entertainment

Glad I don't watch that cruelty, kinda like the redundancy of this beat thread.