Subfloor replacement

I noticed a soft spot in the companion way and forward stateroom of my new to me, 35 year old 41' PT Europa Trawler. I have discovered that the 1/2" plywood subfloor has delaminated. Not rotted, just delaminated. I feel like the problem was caused by a 1/2" or so of water that remains on the false floor because the bilge pump and float switch cannot be mounted low enough. It's only about a 1 1/4" drop from the flat false floor in the forward part of the boat to where the float switch and pump sits. I'm thinking I could correct the cause of the problem by installing a small diaphragm pump (1gal./min. or less)with a cycle timer that will cycle the pump on at set intervals and run for a preselected time to keep all the water removed from the bilge. The two existing bilge pumps will remain functional, in the event the small diaphragm pump fails or a major leak occurs. Anyone have other ideas on how to keep the water sucked out of a shallow bilge well???
Also any recommendations as to what type of 1/2" subfloor to go back with??
I'll be reusing the 3/8" teak parquet flooring that I removed back over the new subfloor.
Thanks in advance for any recommendations.

Don

Greetings,
Mr. P. When people have redone their outer decks, some have used a synthetic underlayment (of course, I have no idea what it is, as per usual). I am trusting of those members whose memory is actually intact to help out here.

The collection of water raises some questions...Is this a design flaw of this particular model or would adjustment of trim of the vessel eliminate the pooling/collection of water? Meaning, if you could trim bow or stern heavy would this help?

Might it be possible to fill the void? Maybe pour in a resin/epoxy of some sort? Perhaps a pour-able foam?

Where is the water coming from? Overflow from somewhere else?

I'd hate to admit that there could be a design flaw in my fine vessel. LOL
I do however think there was a bit of poor planning when it came to the bilge , as far as how it drains to the Bilge pump. The only leak I'm aware of is the normal drip from the shaft packing. The other question I'm asking myself, is what's under the false fiberglass floor. Is it a empty void, or is it full of trapped water. I've thought about taking a 4" Hole Saw and doing a little exploring??

Our 38' 1984 Fu Hwa Europa has displayed some of the 1/2" plywood delamination. The ER center floor, under that awful aluminum diamond plate, was one place. Another is the plywood under the berths. Our floors are solid Teak and Holly over plywood. The floors are fine, even up forward where water collects to about 1"+ deep (about 12" below the sole). (The boat seems to trim down by the stern, due to the dink on davits, but there's still water forward. A fix I've planned but not installed is to add a small bilge pump to move the water back to the main bilge sump.)

My vast engineering knowledge (as a retired Architect) suggests that the delamination is really caused by 'rolling sheer'. This is a typical failure in plywood where the stuff is too thin for the span/loading. Since your parquet provides nothing for stiffness or strength, your subfloor has to do all the work. Replace it with thicker, 3/4", plywood. and reinstall your parquet.

Since you probably are unenthused about replacing the whole floor, consider replacing the failed areas with 1/2" plywood doubled between the supports with another 3/4" thick bit of plywood underneath. I think, I say 'I think', you'll get away with this even though the thinner plywood will want to bend/sag over the support joists. Additional support for the plywood in between the joists can be added by adding 'ledgers' to the joists to support it.

I replaced my ER floor with 3/4" PT sheathing grade plywood and added an anti-fatigue mat to crawl around upon. I have not replaced the under-berth plywood; though I sit there, I have not fallen through.

pressure treated plywood at home depot is guaranteed forever against delamination and rot. Unless I am putting in finish wood, I use pressure treated.

If you can use 3/4". It will be difficult at best to keep 1/2" from deflecting when you walk on it if the span is much bigger than a foot or so. Too much flex and it can pop your teak parquet off.

I think I'd spend some time figuring out where the water is coming from. It sounds like it must be a local leak, maybe from the deck somewhere?

I agree with the thicker plywood. Also you might want to epoxy coat it before you install it since it is so close to the water in the bilge.