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I may have seen this in a book, so probably not an original thought, but I think you have "zones" as vessels become aware of each other.
First is the evaluation zone. You look, visually, at lights, at radar (and AIS and ARPA/ plotting,) if you if you have it, and figure out if you have a close-quarters situation.
Second is the reaction zone. You realize you have a steady bearing-decreasing range situation, figure out if you're the stand-on or the give-way vessel, wonder if the other vessel is aware of you, maybe you get on the radio, and try to sort it out. If you're the give-way, this would be the time to make a sharp course change as a "signal" to the stand-on that you see him and realize that someone has to make a course change.
Third is the "avoiding action" zone. Here's where the give-way actually gives way, and when the stand-on makes sure he is..
Fourth is the "I gotta get out of this now, or we'll collide" zone. This is when the stand-on vessel can alter course and speed while there's still just enough room to avoid it even if the other guy is asleep at the wheel/autopilot. Here's where the danger signal comes in, if not sounded earlier.
Fifth is the "it's too late/general alarm" phase. Give-way hasn't given, stand-on hasn't taken sufficient action, and you're going to collide, only question is what type and angle of collision it will be.
I don't need to say what the sixth zone is, except you don't want to get there.
I've mostly been thinking of crossing situations here. The toughest are the not-quite-head-on, when one vessel thinks green to green is acceptable, while the other doesn't and alters to starboard. A recipe for a hit or a near-miss.
And in fog, bear in mind that Rule 19 trumps all the other meeting and crossing rules. There's really no "right of way" in fog. All vessels of all types have to navigate with caution until any close situation has passed.
These zones may be miles apart for fast oceangoing vessels, or only a few hundred yards apart for smaller recreational boats at a harbor entrance, and can expand or contract depending on visibility, weather, sea state, darkness, lots of factors.
And these zones depend on both vessels seeing each other, visually or electronically. If they do, usually things work out. If one or both of them don't, then they often don't.
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