It depends (Standard answer). If we saw some pictures it may be a big help here. If the cabin sole is plywood, it will have a really thin veneer as a top surface. Depending on the amount of damage it may not be salvageable. Light sanding with 220 grit should tell you how deep the damage is. Some folks have had some success with bleach but be really careful with it. One drop in the wrong location can leave you with a bigger refinishing job. If the damage doesn't penetrate the veneer, you should be able to sand it down and refinish it. Otherwise, you may choose to replace it or to cover it with some sort of laminate. Depending on where the damage is located you may get away with only doing part of the sole.
That is water damage with a side of mold.
In my experience repairing panel 3087 is possible. The "How" will require further study and responses from the group. Don't forget to search the archives on this site.
Are panels 3088 and 3089 the underside of 3087?
Try some steel wool and lots of elbow grease, start with medium then go to fine in direction of grain. That's what I did ,then some stain and then sprayed from a can polyurethane and my floor came out better then new no brush marks. If use sandpaper it will cause deep grooves and the teak and holly is a veneer and thin. You can chemical strip first then steel wool
Steel wool is no problem ,I did all my floor and there is no rust, it is what is used by furniture restorers . Steel wool is a finer finish then sandpaper and there is no way it would get embedded . I then used a tack cloth before staining and before using polyurethane and sanded between coats with fine steel wool and tack cloth
I'm with Ken Cross - "it depends" - and in this case, largely on what you consider an acceptable result. Looks to me like your sole is plywood w/ T&H veneer, but correct me if I'm wrong. If it is, that gives you about 1mm of material (T&H) to sand to an acceptable state and then refinish. That isn't a lot to work with but maybe worth a try. Your other pictures show that the plywood is separating on the underside. Common for production boats of the era as they didn't epoxy/seal the floor boards. So really 2 issues to deal with. As long as the unevenness of the bottoms doesn't prevent the floor boards from being reinstalled securely/evenly, you can probably live with that since it will be out of sight.
If the boat is in good shape otherwise, and I intended to keep it, I'd put the old boards back for the remainder of this season and replace the entire floor with new T&H plywood over the Winter. Largely this opinion is due to certain issues I have surrounding OCD, so YMMV.
Either way, good luck and let us know how you make out.
We mostly restored a badly stained and moldy T&H (ply) cabin sole. First took the sections to a furniture dipping company to clean them up. Then a light sanding and multiple coats of varnish.
For smaller projects we rely on TeKa "A and B" cleaner and neutralizer.
Of course, YMMV, so be cautious. Until you sand too much and blow thru the veneer, it's difficult to know just how much surface wood is there.