Simple Simon wrote:

It's simple. Information is not scanty when

1) I hear the fog signal of a vessel forward over a period of time and
it's bearing is not changing and the signal is getting louder.

Fair enough. But first, please, show me a reliable method of taking a
bearing on a fog signal. I only seem to be able to achieve a precision
of plus or minus 180 degrees, or plus or minus 45 if lucky.

2) I must follow the Rules that states if there is any doubt that a vessel
is on a collision course then assume it is indeed on a collision
course.

Backwards logic again. Rule 7d1 says risk of collision shall be deemed
to exist if you are on collision course (i.e. if the compass bearing
does not appreciably change).

That doesn't mean that if you are apparently on a collision course
(by magically sensed compass bearing of a foghorn) that you should
assume you are on collision course, from which an arbitrary change
of course will divert you.

3) I know Rule 8 states a course change early and pronounced is perhaps
the best way to avoid a close quarters situation so I follow Rule 8
and change my course early and evidently so as to avoid a close
quarters situation.

The purpose of 8a/8b/8c is in big part to ensure the other vessel's
master is made aware in good time of your action. I'm more concerned
about the rest of rule 8 here. You can't hope to comply with 8d
(action ... to result in passing at a safe distance) if you have no
way of assessing what that distance is likely to be because you have
no precise enough idea of its relative position. And again I remind
you that even when 19e doesn't apply, 8e also tells you to slow down
if necessary to avoid collision.

What kind of course alteration are you proposing, by the way?
A U-turn? Sounds like a good legalese trick to disarm 19e,
since it would automatically change a fog signal detected
apparently forward of the beam into one abaft the beam. That
would certainly for the moment exempt you from 19e's slowing
down requirement unless it had been determined that RoC exists
or that a CQS could not be avoided. But what if you're surrounded
by fog signals? Then what?