As a former owner if a sign shop, I'll tell you that there's no magic bullet. Sometimes the eraser works very well, sometimes hairdryers work, sometimes you need the heat gun. As others have said, stay away from the razor blades. I've found that the hairdryer and fingernails, in most instances, works the best to get the vinyl started, then you move the hairdryer to loosen the adhesive enough to pull up the vinyl with the adhesive still attached to the vinyl. That's the goal. Sometimes the heat gun will be too aggressive on the adhesive and it will be left behind on the hull. You then need an adhesive remover (like 3M Adhesive Remover) to get it clean.
I've done lots of vinyl removal and sometimes, depending on which side of the boat is more exposed to the sun and the color of the vinyl, one side will come off really easy and the other takes forever.
Sorry that I don't have the magic cure, but be persistant and you'll get it. There will be a ghost if it's been on for some time. Compounding the hull will usually take care of that.
Good luck!