According to reports, shipbuilders are capable of building cruise ships even larger than Royal Caribbean International's planned 6,000-passenger Genesis vessel. But whether passengers and ports are ready for future behemoths is another question, cruise-industry officials said Wednesday. There are no basic technical constraints to further size increases, Maurizio Cergol, cruise vessel chief designer for Italy's Fincantieri shipbuilding yard, said during a panel discussion on megaships at the Seatrade Cruise Shipping Convention, the cruise industry's annual trade show at the Miami Beach Convention Center. Cergol's vision of virtually limitless increases in cruise ship size in the future was echoed by Tom Degerman…