Impeding the passage of a tanker. This was quite a few years ago, only a few after 911, they were a tad touchier back then. They didn't cite chapter & verse, but it was chilling enough, glad it didn't get that far.
Funny you should mention that Stu as I had a similar situation back in 2006. I had just left a yacht club near the Montreal harbor on the St.Lawrence river , hoisted the sails and was getting the speed up when my 12-year old grandson told me we had dropped a fender overboard. Quick 360 look-see to view the situation Re ship movement, then a 180 to go pick-up the fender, another 180 to resume course, a quick wave to a small CG boat traveling at speed with 3 people on board. Everything duly noted in the logbook, including the CG meet and wave.
Got a call from my wife that night mentioning that a CG officer had called wanting to speak to me. He had left his name and number so I called him back the next morning. He told me the small CG boat had reported an dangerous manoeuver from me, in front of a ship in the harbor. He gave me the time. I did the same thing and told him I would look up in my logbook. Then told him that exactly at that time my logbook was showing a ship and I gave him the ship's name, mentioning that that ship was anchored, that a commissary supply ship was on its side delivering supply, and that a refuleling barge was on the other side, also attached to the ship. I was at least 1/4 mile away from a non-moving ship and there was no other ship movement in the harbor.
The officer then told me that the 3 people on board the small CG boat who had reported me had not mentioned my waving at them, or that the ship was anchored. I questioned why they did not come by and tell me themselves what they had seen. He could not (would not ?) answer that, but he did say that they were 2 trainees and a junior officer. Of course he did not mention names, but did commend me for such an accurate logbook and apologized for having created some worries for my wife !
