Who’s at fault in a Shipping Lane collision?

I was recently a passenger aboard my brother in-law’s motoryacht during a pleasure trip to Catalina when we had a close encounter with a merchant ship. We were in fairly thick fog and we were steering a compass course from the flying bridge helm station when we heard a loud series of blasts from a ship’s horn that was obviously very close. My brother-in-law ran down to the lower helm station to look at the radar, and he was able to make a hard right turn to keep us out of trouble. In hindsight I felt he did a number of things wrong, including his failure to look at the radar or monitor the VHF radio, but the biggest problem was, in my opinion, we were in an established shipping lane in a time of limited visibility. If there had been a collision would he have been responsible? Our reader is interested in whether the use of shipping lanes by a pleasure boat, or the failure to monitor radar or a VHF radio, could lead to a finding of fault in a collision. We will address those issues, but we should note the Navigation Rules (commonly referred to as the Rules...