The 4th amendment-The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.
1. Did he seize anything?
2. I'm assuming he did not conduct an active search through the boat because you stated he "requested" to see various safety items and documents.
His reasonable suspicion was the erratic maneuver you described. The same thing might have happened if you dropped a lit cigarette in your lap while driving your car and you swerved out of your lane while trying to find it before it set your balls on fire(don't ask me how I know that). I'm surprised that you don't know this. It's boilerplate. And be glad the Coast Guard didn't pull you over. They like to disassemble your boat looking for stuff, and it's all FEDERAL(those guys have more power than a U.S. Marshal!), so the court cases are federal cases. This means that if you have 4 people onboard and only have life jackets for 2 of them, that's potentially a $2000 fine!($1K per life jacket). Boating is a VERY highly regulated activity.