"Insufficient info" really to try to assign blame, which is your inquiry here. But look at the rules. In thick fog, all bets are off, except for the rules which apply in fog.
Forget about almost all of the "vessels in sight of one another" rules (meaning rules 11 thru 17, which tell you who is the "stand-on" or "give-way" vessel, and what each should do).
Legally, you're now in the realm of "Vessels in Restricted Visibility". That's Rule 19. Both vessels shall keep a safe speed considering the visibility (which could mean bare steerage or even zero speed in zero vis), watch that radar or AIS, sound and listen for foghorns, determine if there is a close situation coming up, and navigate with caution, etc (the rule sets it all out).
So no one is privileged nor burdened in the fog. Sail, fishing, anyone, have the same obligations--to be cautious, determine if a close-quarters situation may arise, and slow or stop until you both figure it out and get past it (radar, radio, and now AIS, and even whistles can help in sorting things out).
I'm not sure mariners in general realize this, though Rule 19 has been around since the stone age. They still think, "sail over power", or "trawling over sail", etc. Those rules no longer apply in fog.
Leaving wheelhouse on autopilot doesn't sound like the "navigate with extreme caution" which rule 19 requires when there's a vessel ahead of you in the fog. But what was the cat doing? Did either of both have radar? Anyone watching it? Signals being sounded by both? Any radio contact, or attempt?
My initial reaction is that the "cup of tea" mate may have a problem under rule 19, as well as the "lookout rule" ( Rule 5). But these questions are very fact-intensive, and can't be answered without more info. But don't rely on the "in sight" (meaning visual, not radar) rules to determine the obligations of vessels who can't see each other in the fog until they near-miss or hit each other.
Re-reading Rule 19 now and then is a good idea.
Last edited by nolatom; 07-15-2008 at 12:27 PM.