You can use some kind of drill roto flex , is kinda something for grind and open cracks , nice for reaching tight spots , around corners etc... striper for gelcoat
i dont recommend , many stripers soft polyester resins, when you have the cracks deep open and the surface around free of gelcoat
, pour some thin epoxy
in the cracks , fill the cracks with thick epoxy
mixed with silica and glass the top , finish with epoxy primer or whatever you like it....