from the website...
p.s. I've done this twice, so far. Please check the website, I don't like the way this copied and pasted.
Future Cruise Consultant
While onboard you can book your next escape with Princess. Future Cruise Consultants are on each vessel to advise you of future cruise itineraries, fares and incentives. By booking onboard, you will receive reduced deposits of $100 (USD/CAD) per person and up to $150 shipboard credit on your next sailing with Princess.
Simply make a deposit toward any cruise to secure this exclusive offer available only to our onboard passengers.
Unsure of future travel plans?
You can still take advantage of this rewarding program — just place a low deposit while onboard of $100 (USD/CAD) per person, and take up to four years to sail on your next escape with Princess.
CRUISE LENGTHSTATEROOM TYPEONBOARD CREDIT (USD/CAD)*
7-9 days Interior
$50 10-15 days Interior
$100 16+ days Interior
$150* Shipboard credit applies to the holder of the Future Cruise Deposit only, and is not applicable to upper berth passengers.
Check with your Future Cruise Consultant about offers for World Cruises and the International program.