Last year was the first year my Master Card showed the added fees about 2.5% in both the BVI and USVI. When I called they said it was a new policy that was covered in one of the mail outs with bills some time ago.... being on a boat
in the Carib... I didn't get the memo. Prior to leaving this time I called around. Only the American Express did not have the fees unless I was converting dollars to another currency. However their base interest rate was higher than the others and fewer places will accept American Express due to their huge fees they charge the companies that use them.
Best bet if you are going to be down for a while is to open a local bank account (debit seems best) and transfer/ wire in funds. You may get a one time wire/ transfer fee but no other fees. While traveler's checks use to be a good idea... fewer places are accepting them and some places only accept cash.
You do not want to be caring around on you or on your boat
any large amounts of money. Making occasional withdrawals from your local bank saves money and problems and is worth the hassle if your going to be around the area for more than a couple of weeks. Check out USAA if your prior military or Dependant/ spouse of one. They have the best policy on no ATM charges worldwide but limits do exist and the rates may not always be great on credit cards.
One warning... in the Carib Credit Card use is far safer than Debit card use particularly with ATM's