Shen,
If you'll notice after about 70 feet most of these boats come with crew
quarters for the reasons you state. A boat that large involves a lot of work
that most people that can afford the boat can also afford someone else to do
the work. I'd guess 60 foot would be the upper range for a couple to
operate. Have you ever heard of an insurance company denying coverage due to
experience?
Paul


Say you hired a crew for this boat. How many would you have? Maybe a Capt,
Mate/cook? in other words, a couple.
There's nothing that would keep two people from handling a 60 or even 100 foot
boat competently as long as they know what they are doing and the boat is well
equipped.
Insurance companies and banks tend to want to protect their investments, and
set up rules which must be followed to obtain their insurance and loans.
Aside from them, there can be other regulatory hoops to jump through, so I
can't give any specific answer as to requirement which may be specific to all
sizes because there are just too many variables.
For instance, I know of 550' ships that are certified for a crew of six. Not
totally in line with the question, but it gives an idea of the possible
variables involved.

Shen