Best way to waterproof plywood transom

[tank1949]

Unless you never ever expect the PT to get wet, never ever, best to not use PT in an aluminum boat.

Its not just about transom contact, its chemical leaching and collecting in seams to. As seen in lots of topics posted here

100% agree, but owner has to see the cost effectiveness for the long term. Galvanize bolts against aluminum doesn't work well either. You can defeat the problem by adding SS as a barrier, like SS washers.

 

[jimmbo]

One thing about sealed wood, or what was thought to be sealed, if any fresh water does get in, it will never get out, and that is when the Rot starts. Salt Water doesn't seem to rot wood as fast

 

[tank1949]

One thing about sealed wood, or what was thought to be sealed, if any fresh water does get in, it will never get out, and that is when the Rot starts. Salt Water doesn't seem to rot wood as fast

As fast.... Indeed, water will always find a crack or screw hole. I have replaced 2 I/O saltwater usage transoms. About 12 years life on a Proline and 30 on a Sea Ray. Rot seems to always start at the transom drain. These were trailered boats. My latest transom, I even coated inside of transom assembly bolt holes. Until a person has replaced an I/O transom, they cannot appreciate the extra effort required to reduce rot.