Repairing Boat Floor/Deck

Question
We're looking to update and repair our boat.  It's a 1986 Raven (I believe) and one of our main projects is repairing the flooring.  I'm not finding much information on the topic, and then I came across this site and I'm hoping you can help.  My boyfriend was simply planning on removing the old carpet and then applying new marine-grade plywood over the existing flooring (to make it "doubly-strong"), treating it with all the appropriate materials, and then putting down new carpeting.  Do you think this way of repairing and updating the flooring is wise, or should we totally remove the old plywood too?  In his mind it makes more sense to just add another sheet of plywood to the floor instead of removing the old and putting down new (it'll make the floor stronger).  Plus, I think he's trying to do this with as little work/time as possible, since there are so many other things to do.

Any help/insight you could offer would be GREATLY appreciated!!

Thanks,
Michelle

Answer
Hi Michelle

Thank you for selecting the undersigned to reply to your question.

The original plywood flooring likely contains a substantial amount of moisture, which in time creates the growth of mold, and in turn, the wood begins to soften and deteriorate. Laying new material over the existing plywood traps all pre-existing moisture within the former material, and ultimately, it is transferred to the new flooring, which will eventually absorb that moisture,and the cycle repeats itself again.

It is absolutely imperative all of the old flooring be removed, including affected stringers and/or framework that supported the floor, because they may show signs of soft wood called dry rot....it smells and the mold is definitely unhealthy for the lungs.  

Then, apply new marine grade materials, where the laminates are secured together by a waterproof adhesive or glue. Figuratively speaking, ordinary glue binds construction grade plywood, which does not use waterproof glue.

Do the job right the first time, otherwise, in a few months or so, you'll be doing the project all over again at twice the cost, if not more.

Safe Boating
Ron Blanchet