I've been stopped by the coasties twice. Both times I was doing something a little strange.
The first time I was running back and forth in front of the port of Miami by myself. There was a measured mile there and I was doing time runs but I think it looked strange to the coasties. They were very professional and polite.
The next time I was headed offshore, by myself, in heavy weather that kept most boats in. I just wanted to see how Possum handled in bigger waves. I think this looked strange to them. Again very professional. Because of the sea state they asked me to go slow ahead into the waves. They came alongside, never touching Possum, and two men jumped aboard. I showed them the papers the first guys had given me. They thanked me, their boat came alongside, they jumped back and left.
Both boats were armed with a machine gun, M60 I think. The boarding officers all had hand guns.
I experienced a third boarding on a friends boat. We were very glad to see them as our boat was sinking. They brought us a big pump and we were able to get ahead of the water and save the boat. Those guys were really great!