It looks like the wood in my stringers is wet. One side had mush on the top, but good wet wood on the bottom. I cut it out. The other side just wet, wood is still good. I'm pretty sure I will cut it out as well. If I cut the top of the fiberglass off the wood stringer, do you think it would dry out?
No, you will never get enough ventilation for it to completely dry out and if you cut all the fiberglass, you just might as well replace it, you almost there. Wet wood will rot eventually. Better replace it while you are at it
I went to lowe's and just scooped some wood out. I found some composite flooring that I could use that would never rot. What's your thoughts on composite materials ?
These materials are not designed to be a stringer core. You need to use lumber or external grade plywood. If you want composite core, there are material out there that are designed for this specific purpose but they are pricey. Wood - done right - will get the job done.
Would poly resin stick to it? Did not try but again, this material is not designed for this specific application
I also found out that the middle stringer that goes from the drivers control area towards the bow is completely gone. But it goes under the bow fiberglass and I can't get to it. There are three total stingers in the front, and the two outside are good. Does this middle stringer, that's maybe 5 foot long, cause any real structural threat?
Yes, otherwise the designer wouldn't use it or add it to the design. I think you got a full restoration on your hand but without pictures, I can't be sure. Post as much pictures as you can so we can see what you see
The fiberglass is real thick around them.
it doesn't matter, they are not glass stringers so they get the majority of their strength from the wood. Glass needs to be thick enough to keep the wood in place and transfer the load to the vessel's hull but not the source of the strength