I am looking for anyone with Judging experience. I race in the river and rule 19.C comes into play all the time.

"While boats are passing a continuing obstruction, if a boat that was clear astern and required to keep clear becomes overlapped between the other boat and the obstruction and, at the moment the overlap begins, there is not room for her to pass between them, she is not entitled to room under rule 19.2(b). While the boats remain overlapped, she shall keep clear and rules 10 and 11 do not apply.”

Does this mean at the moment of overlap you must have room between the boat and the obstruction after overlap you can call for water, or you must have room to pass the boat requiring you both boats to hold course during the length of the obstruction?

If there is not room to pass when the overlap begins you enter at your own peril and must keep clear. If there is room and you obtain an overlap from that point until the the obstruction or overlap ceases the other boat must give you room. Shallow water, docks or a shoreline would be an example.

I guess we struggle with is depth and the shoreline. The shoreline is not straight and someone can tuck into overlap and immediately call they have overlap and ask for room.

That's the tricky part of a shoreline as a continuing obstruction. Who's to say how shallow is too shallow. What if the other boat draws more or less water. My suggestion is to discourage the the overlap by pointing out ' You know it's shallow here if you go inside me you might run aground'. Then you get to laugh when they run aground.