Norwegian also uses a point system that starts with the second cruise and is one of the easier programs to reach such perks as priority check-in, discounts, onboard credits, some free Internet minutes. The top tier offers a free bistro dinner with a bottle of wine, concierge and laundry service.

Carnival passengers are ushered into the loyalty VIFP program after their first sailing and get a free beverage at brunch during future cruises. An invitation to a cocktail party follows a few weeks of cruising. Additional cruises result in priority check-ins and such extras as free laundry and specialty restaurant privileges.

After one cruise, Princess members are awarded savings on future cruises of about $100. From cruises 6-16, passengers get an atlas, preferred check-in, and some daily free Internet use. Other perks, following additional cruises, include shoe polishing, laundry, priority disembarking, cabin canapés, tea service, opportunities for discounts and cabin upgrades.

Returning passengers on Holland America receive Cruise Day credits as Star Mariner and a champagne brunch. Discounts follow as cruise days increase. With 200 come larger discounts, laundry service, and a free cruise for the third and fourth passengers in a cabin on select sailings.

Celebrity’s credit system is in three tiers. The second tier requires five credits after five cruises or fewer, depending on length and cabin choice, and includes discounted Internet and laundry service. The third tier, after 10 credits, includes free Internet and laundry, as well as access to the Captain’s Club Lounge.

At one end of the cruise line loyalty perks is the traditional private cocktail party that many ships offer to second-time passengers. These days, with big ships and lots of repeat cruisers, the massive, crowded cocktail party is not much of a special perk, and cruise lines are rethinking what to do about it.

At the other end of loyalty perks is free Internet time at sea, much prized these days and not that easy to get, because cruise lines make money on Internet time through contracts with wireless carriers.

While most Internet communications run much slower aboard ship than at home, cruise passengers want to send and receive email and keep up with news.

The Internet perk for loyalty cruisers varies substantially among cruise lines — from no break at all at bottom tiers of the loyalty programs to a pack of free minutes. On Cunard, for example, World Club members need to complete only two voyages or 20 days to get two hours of free Internet time on subsequent sailings. For an Internet discount on Princess, you need cruises totaling at least 51 days at sea (for about 15 free minutes a day). On Oceania you must spend nearly two months at sea for an Internet discount.

David Molyneaux writes monthly about cruising. He is editor of TheTravelMavens.com