Sorry - but it is not clear
It works great if it is a large commercial vessel. But recreational boaters don’t necessarily follow perfectly straight trajectories.
They are turning around to look at the babe on the boat that is passing, they bend down to get another beer out of the cooler, or they just kind of wander about.
I look at the very point of the bow as a start - which side of the boat is most exposed. But I often find the bow moving left to right and back again as it approaches at high speed, bouncing off the chop. One moment it will pass behind me, the next it is angled to pass in front of me.
I think you believe what you posted is proof that everyone else is a novice lacking in this great skill - but the fact is, the human brain is really incredible in its ability to judge trajectories. If you doubt that, just throw a ball to a 4 year old and watch how they determine, in less than a second, just where it will meet their hand.