Answers annotated below.
It sounds like this vermiculite is between the hull and the floor in the area between the engine and the bilge and stops water from draining aft of the bilge into the bilge. I gather the consensus is that this vermiculite serves no purpose and can be removed? It seems terrible that nothing aft of the bilge will drain on this boat. I also have to replace the large bilge hose (as shown in the photo), and I assume the only way to do this is to remove the floor? This boat is so dirty in every way imaginable...
The vermiculite absorbs water like dirt. It rots and expands - it also stinks when you expose it. Yes - you need to remove the floor. Unfortunately the great pictures Rich had on the Tres Cosas rebuild are no longer accessible. He did a great job documenting what he accomplished on the rebuild.
Where exactly is this “second bilge” I’ve seen referenced?
It's the void between the engine pan and the main bilge. The water most see is from what was absorbed on the Vermiculite.
I guess people started drilling drain holes in the engine pan? I have water accumulation here because of a leaking stuffing box. It’s seems as though a water tight pan is meant to catch petroleum products and fluids that shouldn’t go in the bilge?
That was me who started the thread about drilling in the engine pan to access the hidden bilge. Don't do it!
Any idea where the hull numbers are located?
The hull id number (HIN) is originally stamped on the upper stbd side of the transom and usually start with TSP then a series of numbers and letters. If you know who the previous owner was, or have a sail number, it may already be in the class database. Sometime the HIN gets covered if the boat is refinished.
What are the signs of wet core, and where exactly in my photo?
All that cracking around the center bilge section is a sign that water was behind the glass in the core, froze, expanded and cracked chunks of glass out. When I had J/30 Rhapsody it was similar.