Lots of options:
#1 - Believe it or not, a damp soft cloth and a couple tubes of toothpaste will probably work and your boat won't get cavities! Toothpaste contains a very fine polishing abrasive and unless you buy the stuff made in China, nothing like silicone, petroleum products, etc.
#2 - Automotive polishes like 3M "Perfect-it", "Finesse-it" and "Imperial Hand Glaze" are compounds that don't contain anything that would repel future repaints.
#3 - Go to the automotive department at a place like Target. Buy a pack of white cotton diapers (you won't find a better hunk of soft cloth for polishing painted finishes). Then buy a tube of "Scratch X". It's another fine abrasive used for polishing out scratches and removing oxidation. The abrasive in it is kaolin (a type of clay) and you use it by rubbing small areas until the compound is pretty much gone. As you rub, the kaolin particles slowly break apart, getting finer and finer. It takes some elbow grease, but is great stuff.
Any of these polishing jobs will last longer and likely look better if you wax them afterward. Target also sells a car wax/polish from called "Zymol Cleaner Wax" (blue bottle @ about $11). Unlike almost every other wax out there, it's water-based. It's great stuff and some of the best show car finishers and electric guitar refinishers in the world use it because it is all natural ingredients and it can be removed easily in case the thing ever needs to be repainted.
