FourthAmendment.com points us to an article by Clark Beek that begins:
Sorry, but when it comes to Coast Guard boardings, you don’t have any rights.
I’m surprised how many boaters don’t know this. The US Coast Guard can board your boat any time they want, and look anywhere they want, without probable cause or a warrant. They can do this on the open sea, or while you’re asleep aboard in your marina at midnight. They can look through your bedsheets, in your lockers, in your bilges, in your jewelry box, or in your pockets. They can do it carrying just their sidearms, or they can do it carrying assault rifles. They can be polite about it or they can be rude, but mostly they’re polite.
Read more on SailFeed. The article really was an eye-opener for me. I’m filing this in my “I didn’t know that” file and looking forward to Part 2 of the article.