Originally Posted by rslifkin
I view that issue as follows: I'll maintain course and speed, but if I'm getting close to the point where I may lose my ability to take evasive action and the other boat is not taking suitable action, then I'll alter course or speed as necessary to resolve the conflict.
Rule 2 quoted below pretty much answers your question related to situation 1, and pretty encompasses what people studied in the COLREGS call the General Prudential Rule and the Rule of Good Seamanship.
"(a) 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
(b) In construing and complying with these 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."
Part (a) says don't be stupid and be a good seaman while Part (b) says you can depart from the rules if the circumstance is 1) special and 2) immediately dangerous.
Was the narrow channel situation you described "special?" Probably not because it only included two vessels in a situation well covered by the COLREGS. So INITIALLY a departure from the rules would not be necessary until the situation developed into one of "extremis" (a special circumstance) where only action by both vessels would be required to avoid collision.
Let's say for a moment the small vessel coming out of the marina sounded the required one prolonged blast of the ship's whistle or, in the case of a vessel under 12 M long, and efficient sound device like a handheld air horn. Thus alerted, you would be aware you had a vessel about to approach from the stbd side. Would you have slowed or clutched to neutral as a precaution? I mean he hasn't yet showed up as a danger, he just made a noise getting underway.
While some may think boats exiting marinas along narrow channels should wait for vessels in the channel to pass as a courtesy, what do the rules actually say? Rule 9(d) says for vessels not to cross the channel, and Rule 34 says you should have hit the horn button five times if you saw immediate danger. If it was not immediately dangerous, Rule 34 (a) is your whistle guide.