I have not personally did this but it was our plan May 2013 however, the weather was uncooperative. I did research ahead of time and contacted the Sheraton because it seemed more along the lines of what we were looking for. Yes, public transportation or a taxi is needed. Here is some info that I think will help.
The day pass is $99.00 for a room of 2 persons and each additional person is $10.00 with a maximum of 4 persons to a room. Otherwise (without room) $30 per person and children (4-12 years) $15 per child. These prices are for the use of the facilities and the passes can be purchased at our Front Desk upon arrival. The passes are unlimited so you should not encounter a problem. The day room pass can be purchased in advance and are good from 7am-7pm. Both passes includes kayaking, snorkel gear, water trampoline, floatation mats, aqua cycle and paddle boats. Please note resort fees and taxes are not applicable to these passes. The cruise port is about 20 minutes from the hotel by taxi and the charge is around $21 for 2 passengers and each additional $3 or by bus #10 at $1.25 per person.