Tackling this hull post osmosis treatment

[bmrn]

We could have be more helpful quicker if you had mentioned you owned a Verl 27 and avoided comments including mine about running away. Generally the more information you divulge in the initial post will give the best and fastest results.

Hope your repairs go well and you are sailing soon.

I hope I didn't come across the wrong way there, there was no other tone to my message than genuinely being thankful for all the viewpoints. There's a wealth of experience on this forum much greater than my own.

Also, I did say it was a Verl 27 in post #8 after being asked.

 

[fisherman]

As some have said, it doesn't quite look like osmosis, more like a badly done gelcoat. Osmotic blisters are more mushroom shaped in cross section, a surface blister, tapering down to a point in the mat substrate, depth directly related to diameter. Yours seem to just be burst bubbles in the gel coat, from the limited view we have.
If it is real osmosis much comes down to the original hull thickness and integrity. The repair man at Gweek told me that very occasionally the osmosis has penetrated into a thin hull such that it's almost through, and caused it to be written off. Big/deep blisters, thin hull.
If you want any encouragement about repairing GRP under water, I once put a 1m sq sacrificial patch, mat and polyester resin, on my hull, after roughing the gel. Applied over a low water, it was meant to be temporary......twenty years later......twenty years of dragging pots up across it......
I have seen a boat which was entirely coated underwater in 2x600gm mat/resin layup, presumably because of rife osmosis.