Norwegian Cruise Line has decided not to exercise an option to have Aker Yards France build it a third mega cruise ship like the two 4,200-passenger ships currently scheduled to debut in 2009 and 2010.

The two 150,000-ton F3 cruise ships presently on order are the largest ever commissioned by NCL, and when they join the fleet, they will be almost the size of Royal Caribbean's 154,000-ton Freedom-class ships.

NCL provided no explanation for its decision not to exercise its option for a third F3 ship.

Observers noted that when NCL announced the recent $1 billion Apollo investment in the cruise line, it said the infusion would help it "continue to expand what is fast-becoming the youngest fleet in the industry."

Royal Caribbean, meanwhile, is moving ahead with plans to build an even larger class of ships, with the first of the 5,400-passenger, 220,000-ton vessels scheduled to debut in 2009. A second Genesis class cruise ship also is on order.