It is solid fiberglass. But not sure of the thickness, six inches max I would guess
Ed! Six inches? Do you mean the hull would be 6" of solid glass there?
I recently did this job, as you know. From what I can tell on an H25 that hull bottom is about 1/2". A Cherubini 44 is 2-1/4" which is WAY overkill for production fiberglass boats of any vintage. I would estimate that the H30 is not more than 3/4".
The important thing is to know what kind of 'glass is used in this layup. In the 1970s everything was woven roving, shoelace-like ribbons of glass fibers, about 3/8" wide and about 3/32" thick. This was woven at 90-degree angles into a heavy cloth, smooth to the touch (unless you got afoul of the end of one of those individual strands). In fiberglass molding this was usually laid up inside several layers of plain mat (the non-directional stuff Corvettes are made of, thin and flimsy but facilitating a fair, smooth outer finish against the mold).
Then the brainstorm came to bond both these kinds together. This innovation was known as Fabmat-- a trade name from J-M or Owens or someone. It was 24-oz-per-sq-ft woven roving bonded to 16-oz mat using a little bit of polyester resin-based glue. This made layup faster because-- given adequate saturation-- you were laying up two layers at once. The bottom of a C44 is solid Fabmat, about 25-30 layers (I'm guessing; I don't recall). This would sink a Hunter 30 if done there.
Like all boats of the '70s the H30 is undoubtedly done with Fabmat and I could guess about 8-10 layers to a finished depth of about 5/8" - 3/4". Fabmat when cured is very strong-- compare it to the way if you interlock your fingers you can hoist a heavier guy over the fence than if you just lapped your hands one over the other. The secret is the woven roving. It has plenty of crevices to hold resin and to which to bond new layers. It is stiff enough and puncture-resistent enough. (This is what they should have put in the hardware-fixing places on old Corvettes, and didn't. It's why the bumpers loosen and fall off.)
As far as actually changing the bedding compound in the keel, it is easier than you think. Prop the keel in place from outside using good timbers, 2x4s, etc. Make a brace so it doesn't fall over if you were to lift up the boat. Go inside, back off all the nuts to give yourself 7/8" or so of thread. Go round the boat and turn all the jack stands, a little on each at a time, till the boat rises up off the (well-supported) keel. Remember the keel is only about 3500 on that boat-- it's not exactly massive. Whatever would jack up a car would hold it.
Once you have the boat up, block it where it is and scrape out all the old 5200. Clean well. Douse with acetone or styrene. (Gasoline works too, but don't use it.) Get about 3 or 4 tubes of 5200 and empty them (I mean cut open the tubes and get ALL of it) into the gap. Lower the boat onto the keel.
The 5200 will ooze out like crazy. Let it, till you have the nuts back down-- one or two clicks on the ratchet and then stop. Then fair or scrape off the excess 5200 you'll think you've wasted. You haven't. The more that comes out, the more you are sure it's also where it should be. You spend an 'extra' $30.00 on 5200 and you never worry about it again.
Tomorrow, torque up the keel bolts. Another two or three clicks on the rachet and stop.
Next day, same thing. Next week, same thing. Every season, apply a moderate about of pressure. Don't kill them. If you grunt even just a little it's more force than needed. Let the 5200 do the work, not the bolts.
This is all I did with mine and there's no worries. In fact I was in the middle of making new backing plates for the keel bolt nuts and had them backed off again and the yard moved the boat-- picked it up and relocated it-- without warning me. The 5200 held on the keel without the nuts, which were still loose when I inspected the boat in the new place. This is what 5200 does.
Using anything other than regular-cure 5200 voids all my goodwill towards you in your finishing this job.
A little later I checked the condition of the hull strata by drilling a few holes and probing with a syringe full of epoxy. Aside from one small spot I knew was bad I could not get any epoxy to go down the holes and finally just filled them to forget about it. It's as solid as a rock.
