Roadrunner's bang on there. If it's Grandad's boat (lovely jubbly) it will almost certainly be oil pant, a la household or something wonderful like Japlac. Enamel will go over your current bits of paint.
If you have some spraying gear, you won't do better than self-etch. Sikkens is the best I know. Dries almost immediately allowing a very rapid build up, then enamel over the top. I have had enamels dry in an afternoon in this weather to three days if thinned enough for an airbrush with whiter spirit, but they have a lovely gloss and are tough as old boots. I use HMG from my local friendly auto body refinishing suppliers., but any would do. Some love Humbrol, but trust me, once you use HMG you'll never touch Humbrol again! I've painted full sized canal boats and tiddly models with it. I also used it for all the chassis on a kit car and the front and rear bumpers on a fibreglass Reliant Fox 4 wheel van. Marvellous stuff. The boats had the pant put on with a fine roller and "laid off with a quality brush vertically and the gloss was superb.
Halfords tins are OK on knew, known and identified substrates. If in doubt, use enamel.
Jarvo, I would never use chemical strippers as they get in the wood grain and cause problems later.