We had 40 plus years of antifouling that we had to remove. ( looked very much like the above images )
This was applied to a 1964 grp 26 foot yacht.We know Both the previous owners they always scrapped off the loose and recoated .....
Click on page 3 for images PAGE 3
I ended up by using an electric hot air paint stripping gun and a FULL faced dust and Fume mask.
It took a long time to get off and then we sanded the whole of the bottom down with a 150 grit sandpaper.
It was one of them nasty jobs that just had to be done.