The two boat I lettered last year were both out of the water, thank god! I've heard nightmares from my buddy about lettering boats in the water.
Most of the real working sign writers I know use vinyl mask or sign tape etc when needed, it sure does come in handy. Pounce patterns and the like are such a time saver especially if you've got multiples to paint, work smart not hard.
I always chuckle at the stripers that frown upon a pattern or some sort of guide or grid prior to doing a design etc, "that's not how Dutch would've done it" hahaha. They're the same guys that can't start or finish a line crisp and sharp if their life depended on it, I mostly go off the top of my head with striping but when I really want to plan something out I'll pre draw and pattern a design just like a sign. All I know is my #$%* is clean and tight whether I freestyled it or made a pattern, I could care less how it was done in the old school sometimes, I do things my way lol.
#$%* I'm just stoked to make some money painting signs and striping in my spare time, I got better things to worry about than if I'm following some sort of old school rules. Those old time guys probably just made #$%* up as they went along, rules are just the man telling you what you can or can't do man haha.