Attaching Plywood Sole In Wooden Boat Build

I've been searching this forum and have not come up with a satisfactory answer yet, so I am going to try and ask straight up in hopes of getting the correct information.

I am designing the under sole structure in my wooden cabin cruiser (Glen L Vera Cruise design). My cabin layout is quite different from the original plans so it necessitates redesigning the sole under structure.

I would like to have removable sole panels so that bilge maintenance will be easier in the future. Some of he sole will be trapped under cabinetry edges (I think), but most of it will simply lie on stringers and frames underneath. I would like to avoid screwing into the stringers as this presents a place for water entry.

Being an ex aircraft mechanic, what first comes to mind are "L" shaped 90 degree nut plates mounted to the stringers with holes drilled in the sole panels to match locations. However, I think this approach has too many down sides, such as corrosion of the nut plates, fastening of the nut plates ( I only know of rivet mounted nut plates), and the difficulty in getting the holes drilled in the correct locations in the sole.

Assuming that the sole panels rest directly on the stringers and frames, the options for fastening the panels down seem to fall into one of two categories, either directly into the frames and stringers, or into some offset fastener.

So first off, is it necessary (and desirable) to fasten these panels down in the first place. I know this seems like silly question, but I have read in at least a few places where the sole panels are simply held in place by gravity.

Assuming that a fastening method is preferable, are there alternatives to the methods I mentioned? And if so, can someone describe them to me?

Just to add a little clarity to the situation. I anticipate that most of the sole panels will stay down 90 percent of the time and only come up infrequently when I need to get better access to the bilge. There will, however be a few panels which cover storage areas and I am thinking these should not require removal of umpteen thousand screws simply to get the cover off.

 

screw down ply sole and cut in floor storage plates that open and close and lock.

 

Screw your sole down, then remove the screws. Over drill the holes and fill with epoxy, then re-drill the pilot holes and crew down again. Water entry point problem solved.

 

Bilge access can be easy or complex, depending on what you're looking to do. Fully sealed access usually needs a "deck plate" approuch, which are bonded or fastened to the sole, making a watertight seal. This can be costly if needing more than a few square inches of access area. Making your own deck plate is possible but often gets complex, to insure water tightness.

The usual route is to bond the sole to the stringers, maybe with some temporary fasteners to hold things down as the goo cures. These temporary fasteners are removed, the holes filled and a seamless result is available. Bilge access panels would be cut into these plywood sole pieces and depending on how anal you want to get, this can be as simple as a opening perimeter carlin, for the "hatch" to land on to a full up, rubber edge hard fastened deck plate, with scupper channels to drain off boarding water.

I'm not sure I fully understand your concerns, about attachment and/or placement of the access panels, but they can be pretty much anywhere you want. Commonly you'd place a 1x2 under the edge of the opening, with an overlap, so the panel can land on it. There are several other approaches to this as well, but often the most simple is best.