Before we start, a photo for reference.

The area I'm worried about is bottom center of the photo.

Removed drain cover... everything inside looks good and dry.

Carpet coming up.. ugly.

Very odd....

Flashlight and camera says everything is good in here.

Surface mold on floor from wrong carpet? I dunno... Looking for help.

Higher resolution image of soft area after I've picked at it a bit. Any ideas?

After further investigation, it appears this floor may have been replaced once before. Take a look at the white lines I've created in Photoshop. Look outside the lines, and you'll see a cut line which doesn't look like it is a factory cut. Plenty of fiberglass used to cover it up, so at one point it was a nice job, but....

Still looking for answers. Going deeper into the rot area.

New day and more work to be done. The hole is growing. It appears when the floor was replaced before, the previous owner didn't seal the top good enough and it started to rot. The stringers show a small amount of damage at the top, but nothing major. The foam (still covered with some plywood on top left) is dry as a bone.

Took a circular saw and started cutting. Other stringer shows some damage at the top, but it's not real bad. I plan to add a couple more supports here. Let me show you with photoshop...

I'm going to glue some pressure treated support board directly to the stringer (I don't want to nail into them or screw into them) using heavy duty liquid nails. Then at both ends, I'll run boards at both ends. This will help reinforce the structure, but it will also give the new plywood something to mount to. Once it is in place and fitted, I'm planning on putting down the resin and a fiberglass mat. After it dries, I was going to resin the entire floor.

Question for my iboats friends - is my plan a bad idea? I don't want to tear out all the floor for one bad spot, but I don't want to do the job 1/2 way either. HELP