Re: 1956 Blue Star Islander Restoration
Cleaning off a couple different coats of paint?
Then prepping the fiberglass for more glass work &/or filling/fairing before new gelcoat?
Prepping the glass for a longer lasting painted finish then is on it now in a patchwork fashion?
Whatever sander will fit all the contours to get the paint off, random orbit to minimize scratching. Don't be too aggressive, you don't want to damage the underlying gelcoat any further. But if the gelcoat is in poor condition, there is quite a bit of work ahead, that sanding alone may not be sufficient.
I would try some citrus strippers that are listed as fiberglass safe, to remove the layers of paint. Aircraft stripper (Rustoleum makes one) is awful to work w/ but removes most finishes. I DO NOT KNOW IF IT'S FIBERGLASS safe or not.
Do not be surprised to find the gelcoat in pretty rough shape.