Question: Do I Need a Passport to take a Caribbean Cruise?
Answer: Yes, the travel rules implemented by Congress in the years following the 9/11 attacks now require U.S. travelers to have a passport or U.S. Passport Card for all cross-border travel, including by air, sea, and land. The only exception is if you're on a so-called "closed loop" cruise that departs and returns to a U.S. port like Ft. Lauderdale, San Juan, or New Orleans; then you only need a two forms of primary ID to travel.
http://gocaribbean.about.com/od/beforeyougo/f/FAQcruisepassports.htm
Was that in effect in 1998? 9/11 happend in 2001