You don't need any transportation to go to the Great Bay Beach. Just walk around the corner for about 10 min and you are there. I really liked it. We rented two chairs and an umbrella for whole day for I think $15 or $20, do not remember now.
There is a very nice side walk with lots of places to eat and drink. And if you want to save some money, you can go back on the ship for your lunch and go back to the beach for a nice afternoon drink.
And of course, there is the Front Street not to miss.
Have a nice cruise!
Carnival Conquest February 2014
Carnival Sunshine September 2013
Carnival Valor February 2013
Carnival Valor February 2012
Carnival Liberty January 2010