Action by a Give-Way Vessel
The Rule
Every vessel which is directed to keep out of the way of another vessel shall, so far as possible, take early and substantial action to keep well clear.
Discussion
This rule was designed well. It means that for example if you are the Give-Way vessel you are communicating (via the action of your vessel) to the other vessel that you have seen them and are taking the appropriate action. Without this clear communication, you are leaving the other vessel guessing as to whether you have seen them or not.
Imagine you are a Stand-On vessel. Any other vessel on a possible collision course should make you pretty nervous. However, if they communicate to you that they have seen you then your stress level is going to be reduced. The early and substantial action to keep well clear is exactly that communication. Substantial action is best done as a major course change. Rule 8(b) even says that a succession of small alterations of course and/or speed should be avoided.
Communication of knowledge of the situation however is the key. Even in a sailboat racing situation where substantial action is typically not given, the helmsperson of the Give-Way vessel should communicate to the other that they have seen them via verbal acknowledgment and a wave signal.
The rule also says well clear. It does not say by 1, 2, 5, 10 meters. It says well clear. How clear is well clear? Clear enough using good seamanship – that’s how well clear.