That's a good way to lose traps. Larger boats are not going to change course to avoid your buoy. Not cause they want to run over it but because they may not be able to. It doesn't have to be a marked channel. Many rivers and creeks have very small natural channels that the tide keeps open. A boat entering or leaving such a entrance may not be able to even maneuver depending on the tide current and wind, etc. I have, more than once, had to hail a person in a small boat with my PA that he had to move because I could not maneuver. Once I had a guy yell at me that he wasn't going to move because his depth finder said there was 6 feet of water. I suggested that he move over 5 feet or get pushed out of the way. When he moved, he shut up cause he was in less then 2 feet of water...
