If the paint is heavy, I would start with a chemical stripper - then follow up with 80 grit - then sand carefully with 120 or 150.
You do not need to get all the paint off - just remove all the loose and heavy paint so it's down to a thin, smooth coat that is well-adhered. This is the Wildfowler Goldeneye I stripped and re-painted earlier this summer. It has been stripped and re-sealed with spar varnish - ready for the prime coat of flat oil paint (like Rustoleum).