When do the rules allow you to depart from them?
When it is necessary to avoid immediate danger. At the same time they do not exonerate anyone who neglected the ordinary practice of seamen.
Rule 2 (a), (b).
Part of the convention General
Two short paragraphs that carry more weight than any other. First: following the rules does not exonerate you if you neglected the ordinary practice of seamen or the special circumstances of the case. Second: in construing and complying with the rules, due regard shall be had to all dangers of navigation and collision and to any special circumstances, including the limitations of the vessels involved, which may make a departure from these rules necessary to avoid immediate danger.
At sea it looks like this
You are the stand-on vessel and must keep your course. The other one is not turning and you have thirty seconds left. Rule 2 says holding your course «because the book says so» and hitting her makes it your fault too. Turn whichever way saves the situation.
The rule says«Nothing in these Rules shall exonerate any vessel, or the owner, master or crew thereof, from the consequences of any neglect to comply with these Rules or of the neglect of any precaution which may be required by the ordinary practice of seamen, or by the special circumstances of the case.»