I am having the same issue with my American mariner monohull
. I tried doing what you are thinking and I can tell you it is the worst. you need a big flap disc on a powerfull grinder that you wont be able to hold up for that long, fully enclosed eye protection, a good respirator, and loads of time.
frustrated with it I contacted my local shipwright and he said I was going overboard
worrying about nothing. he said I would be doing it for weeks and no matter what I did they would come back because the hull
is meant to flex and give in the waves.
he said unless it leaks
, just sand it and paint