I am new to many finer details in racing rules (forgive me if this is a no-brainer to many of you).
So I had a case recently where I was starboard tack boat approaching starting line, converging with a port tack boat. My "pre-start" course was a little low as I was conservatively avoiding any risk of being over early. Port tack boat, closing in on the starting line on a course that could be deemed "proper" even in post start terms... and observing my pre-start course in those closing seconds to the signal, rightly estimated she'd cross clear ahead. But once the start signal went off, we were within 3-4 seconds of crossing paths.
If port tack boat wasn't there, I would have come up some 10 degrees to a proper course - and with port tack boat there, that would have resulted in a collision. In reality we both maintained our pre-start courses until she (port tack boat) cleared ahead, and only then did I come up to my proper course. So technically...I didn't have to "alter" my course to avoid collision...but the port tack boat's position definitely prohibited me from assuming my "proper course" once starting signal went off.
I did not protest...with vague understandings of Rule 16.1 in mind. But does it indeed apply here - right at the starting signal and start line? Or are there other rules that would come to bear?