I would contact the insurance agent from whom got you the quote, if you used an agent, and ask what the New Hampshire's Best Rating (ability to pay claims) and combined loss ratio (how much it pays in claims vs premium taken in) are. Also, how long has it been writing marine policies, and how are they for handling claims. Make sure the New Hampshire you're talking about is the one that is part of AIG or not.
I did a google search for the New Hampshire Insurance Co. and found an Agent who writes business with them. Maybe give them a call and do a little leg work to satisfy yourself.