CASUALTY LOSS (BUSINESS OR PERSONAL?) tax deductibility question

Assume an individual has a boat where he entertains clients.
(1) If the boat sinks and he qualifies for a Casualty Loss deduction under Sect 165, where is the authoritative literature that guides whether it is a business casualty loss or a personal casualty loss?
I have been searching the Code, common law, and publications.
The only thing I have found is under Publication 463, entertainment expenses that are subject to the 50% deduction.
(2)If the boat that the individual used to entertain clients was subject to the 50% limitation, would it also qualify the loss to be a business casualty loss?

(3) The boat sinks due to an “other casualty” and he is alone on the boat

Can anyone provide for me primary sources on how to view whether the boat can be a personal or business casualty loss? And if he obviously used the boat at times for personal and sometimes for business, where is the authoritative literature on this?

Thanks in advance!