Re: Plywood floor overlay ?
Only you know how far gone it really is. Overlaying the existing deck is almost as much work and expense as just replacing it, I would not overlay - but that is me. If the fasteners are holding tight in the underlying structure and are merely pulling through the deck in one area, and the deck is solid (easy to check by poking around with an awl), you may be able to just sister in some more fasteners and seal off the spots where the tired ones were with a bit of PL. (PL400 through PL900 is floor joist adhesive that comes in calking gun tubes. It is readily available at your local hardware mart. It is superior to liquid nails and probably cheaper because they need no advertising budget as it is commonly used in the construction industry)
The next larger step would be to replace a section. If you do this, replace from joists/ribs center line to center line and across the entire width of the floor. You can quickly do most of your cutting/removal with a circular saw set to cut just a bit deeper than the sheathing. I would use PL and plated fasteners to reinstall. SS hardware is crazy expensive and many manufacturers used plated anyway (this is quickly verified with a little grinding). Unless you are planning on this being your last ever boat, I would also use green-board (exterior plywood sheeting). I know some people will baulk at this, but if your keep your boat covered or garaged when not in use it will last a very long time, a 1/2" 4'X8' sheet is less than $30. (you can even toss a coat of paint on it before installing if it makes you feel better). You can replace a lot of floor for under $50 if you are careful to pull back and reuse the carpet.
There is no sense in being hell bent on doing a leg amputation when all you need is your toenails trimmed. Get your boat back in the water and spend the money on sun, fun, and gas.
