Disclaimer -- I attended law school, I practiced law for 10 years, I ran my own business for 20+ years, I am now retired and starting to teach Scuba.
a. Should the boat operator be liable? Maybe, possibly but absolutely NOT a definite No. The operator is an expert in the operations of a dive boat and has, and should have, a duty of care to his paying customers which includes that the operator do what is REASONABLY PRUDENT to ensure his customers dive safely. To me, being a REASONABLY PRUDENT dive boat operator is going to require obtaining some basic information about the dive history of each passenger and then doing what is REASONABLE UNDER THE THEN EXISTING CIRCUMSTANCES to match the customer with prudent dive practices.
I know this is contrary to what most of the SBrs who post on these threads believe but, as I've written before (all too many times) every party in these deals has an obligation and a duty of care. I do not believe, and I'm pretty sure it is the law in California, that the boat operator's only responsibility is to drive the boat.
In this case, quite frankly, I don't think a 14 dive diver has the knowledge or experience to have sufficient judgment to make decisions such as "Should I dive solo" or "Should I dive this spot that my hired EXPERT has taken me to." Being an expert in any business puts a lot of responsibility on the person and with that responsibility comes potential liability for NOT acting in a responsible manner.
FURTHER DISCLAIMER -- I am NOT saying the operator acted in any manner other than with the highest level of care. I also noted that the diver was said to be diving with "a group" which would indicate to me he was not solo diving. I (we) do not know what occurred in this specific case. BUT, I do not believe it is right, nor wise, to give a blanket pass to the expert in situations like this.
b. Only in a very limited situation, would I allow solo diving off my boat.
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I just saw the prior post is from my wife -- we don't always agree!