I would epoxy saturate all the sides of the plywood, regardless of whether it is marine ply or not. Plywood, if allowed to get wet, will ROT, regardless of what kind it is.
As for cutting the fiberglass tape and removing the existing floor, use a fein multimaster or similar oscillating blade tool to cut along the edge. Most of these tools have a flush cut blade that will allow you to cut right along the hull side and leave a very, very clean cut.
You also don't want to have the plywood right up against the inner side of the hull. Ideally, you'd use fiberglass tape and thickened epoxy to tab the sole to the hull, but chances are very likely you'll need to rest the sole on stringers and floors and only tab the top of the sole to the hull—stringers run longitudinally along the hull and floors run athwartships the hull.
Tabbing is only generally strong in resisting forces in one direction... tabbing along the top of a cockpit sole will resist downward forces well but doesn't do as well if the forces are upwards. This is why bulkheads are typically tabbed on both sides but a sole is only tabbed on one in many cases.
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
—Cpt. Mal Reynolds, Serenity (edited)
If you're new to the Sailnet Forums... please read this To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Still—DON'T READ THAT POST AGAIN.