Too much grinding

Geoff,
I would suggest grinding as much of the added layer of glass off that's disbonded as possible especially where you will be glassing in the new stringers.

Welcome to posting and not trolling! Keep the pictures coming and informing us of your progress.

You may be grinding a previous repair?

My 80 Martinique had quite a bit of this too. You'll have to stop somwhere else you'll grind right through the hull. Like Pete said, I got it as clean as possible under and near the stringers and had to live with this in other areas.

Exactly how many layers are you peeling up?

Around the pylon socket there are additional layers other than the original hull build up.

We peeled up 1 complete layer of roving on the starboard side. center of bilge to chine.

Wow...... So when you reinstall that cup and glass it back in. Your first layer of glass should be smaller in area than the next layer. You have a Prime example of a backerds lay up schedule. One HUGE layer on the bottom and a dozen more on top. The bottom layer became disbonded so the WHOLE thing did. By doing the opposite lay up schedule overlapping each consecutive layer by 1/2" or so you'll have 12 layers of glass bonded to the hull instead of just one big one.

Keep up the good work!

I have a very similar chunk in my garage, but it's just the pylon socket with a mountain of glass around it. The rest of the lower bilge came up in separate pieces after I ground through it in some spots. We all know the proper way to do it now but who knows what was happening at the factory in 1980. Even in 2010 I watched an operator glass in the pylon socket of a SN200, the layup wasn't at all precise...

As I said before, an entire hull layer of roving came up, along with my pylon socket. It didn't matter if the socket was glass down backwards. The hull delaminated along with everything on top of it. BJ also peeled up an entire layer inside his 81 Barefoot.