If it's the player's first URComped sailing, the general rule is they can only have one cruise booked. The cruise lines want to see real play data before they allow someone to book multiple cruises. After the player completes their first sailing and proves they play at the expected level, they can have more than one sailing booked at a time. The number of trips that can be booked is usually based on the cruise line, with some cruise partners having caps. Your URComped host will provide information on any limits. Typically, after the first trip, it is possible to book as many trips as desired, unless the cruise partner imposes a cap.