Transom repair

Hi,
I am converting my vessel from 2 x outdrives to shaft. The transom is fiberglass with 2" of ply as re-enforcement. I am about to glass the outdrive apertures but the plywood is suffering from severe rot. Given I am going to shaft and the transom is 3/4" glass, can I remove the ply without having to replace it? I am assuming the purpose of the ply would be for mounting the outdrives?

 

Grind it out and replace it with Coosa Board is what I would do. Leave the glass intact and paste the coosa too it.

 

Thanks for reply.
Unfortunately coosa isn't available in uk. I have found some flat preformed grp panels which I am thinking of cutting to shape and glassing to inside of transom then lay up from the outside.

 

Make sure it's high density

 

If the transom is no longer required to bear the load of engine thrust, much of the strength requirements are no longer there. Is the 3/4" a single solid laminate, or spread over two sides of the ply ? The biggest problem you have there is getting the holes left where the outdrives were, properly covered, which requires the feathering back of the edges over several inches, giving a smooth transition from the old to the new. You certainly need something to bridge the gaps temporarily, as a backing, while you complete the glassing. But there is no need to put any ply etc in there permanently this time, that I can see.