Very few strippers will actually damage gelcoat
beyond dulling it, which doesn't matter if you are planning on applying fresh paint, which I assume you are. Obviously you want to test a patch inside a locker or something to be sure with whatever you use. If it's an LPU, I'd use an aircraft stripper. Strong stuff, suit up well. It's a nasty job too, requires a bundle or two of rags, wire brushes
, buckets, etc. I like to use the non-permeable type of Tyvek suit for this too, they're terribly uncomfortable but you dont want this stuff on your skin, which is very easy to do when doing a deck
. Repel Tyvek, heavy nitrile gloves with duct taped cuffs, rubber boots with taped cuffs, I would suggest a fullface instead of respirator and goggles, etc. It is water
cleanup though, so when you are done and have ragged up and disposed of most of the nasty toxic remnant, you can hose off everything including yourself. No fun, but the only way to get every last bit of paint out of all those little valleys. Many times in the past I have talked an owner into just grinding off the original molded in skid and laying new skid instead of doing this, it's actually much faster, and gives a nicer end result IMHO.
PS-If it's an alkyd you can use a much less aggressive stripper. Still just as nasty a job though.