Free lance diver does not require workman's comp. your exempt as business owner.

Water craft and vessel will fall under hull insurance if you own a boat. If you charter as for certificate of insurance and ask to be additional insured.

general liability is for what you do not how you do it. (ie underwater).

get a 1,000,000 excess liability rider , cost about $250. yr.

Fred,  If you get the time, shoot me a note.  I would like to get a better understanding.  Sounds like you have had to deal with this. I keep running into cost prohibitive insurance policies.  I have become a new subscriber to this board in effort to get a better handlle on starting my first independent buisness rather than work for someone else.

Cheers... 

Did you contact DAN? They provide insurance to freelance divers at a reasonable cost. I'm insured with them too. Their services are good.