While there may be a significant group of closet "Love Boat" die-hards out there, the image of Cruise Director Julie McCoy is quietly fading away.

Anyway, it would be kind of hard to spot her from the top of the rock-climbing wall. Or to hear her announcing the shuffleboard tournament over the noise of the helicopter flying you to the glacier for your ice-climbing excursion.

"People always used to think cruises were for people older than them," said Dan Hanrahan, senior vice president at Royal Caribbean, the No. 2 cruise line. Even if you were 65, "you'd think it was for someone older."

Killer volleyball games and against-the-current lap pools are the $13 billion industry's way of suggesting that cruises simply aren't all deck chairs and dining-room ice sculptures anymore. And while ships continue to cater to the core baby boomer crowd, the eldest of whom will soon enter their sixties, cruise lines are having some success in attracting the younger set. The average cruise customers have dropped in age from nearly 50 to their early forties over the past five years, according to Royal Caribbean's data.

"We've seen the biggest increases in younger families," Hanrahan said, adding that young couples and singles have also joined the cruise crowd.

"There's a real interest in introducing cruising to the younger set," said Terry Dale, president and chief executive at Cruise Lines International Association (CLIA), whose 20 members make up 95 percent of the industry.

Many ships have incorporated mock nightclubs where the underage set can meet and dance the night away, virgin daiquiris in hand.

TV commercials are careful to show that Dad can still sack out by the side of the pool while the rest of the clan goes in-line skating. That is, when they're not gambling in the casino or watching an outdoor movie or skateboarding. But cruising has also become almost as much about being off the ship as being on.

Ann Adams, 38, a consultant at Allstate Insurance who took Carnival Cruise Lines' Western Caribbean cruise, visited a baboon sanctuary at a stop in Belize. "They definitely had a good mix of excursions, and the descriptions give an indication of how strenuous they are," she said. Some cruises allow golfers to take lessons on board, then tee off at a fancy local golf club when the ship arrives at port.

CLIA's Dale says offshore excursions are only getting more challenging and exciting.

Royal Caribbean's Alaska cruise, which offers the glacier-top ice climbing, also sends passengers by copter to a remote area for some dog sledding. Klondike rappelling is also an option for the willing, as is the basic "heli-hike," in which vacationers are dropped at the top of a mountain by helicopter to hike down.

With its eye on the average age of its passengers, Carnival Cruise Lines, No. 1 in the industry, hosts a singles party aboard its Fun Ships at the beginning of each trip, and the crew makes attempts to group singles together in the dining room.

In addition, the company has added more short cruises in the hope of attracting younger people who may not have saved enough money yet to take one of the longer trips, said Jennifer de la Cruz, a spokeswoman for the cruise line.

And while younger parents may have once worried about containing their children on a ship at sea, many lines now have special off- and on-shore activities for kids.

Staid Beginnings

These floating hotels didn't start out quite so hyperactive. Transatlantic ocean liners, precursors to the modern cruise ships, began hauling wealthy pleasure travelers between Europe and the States in the mid-1800s. Ships were resorts back then as well; it's just that resort stays weren't quite so physically active, and the dress was not what one sees at today's getaways, on land or water. Remember scenes from the movie "Titanic" -- the plush saloons, the dinner jackets and gowns -- and then look at pictures of bikini-clad sunbathers and joggers in shorts on today's excursion boats. What a difference 92 years can make.

The grandes dames of the oceangoing vessels made it into modern jetted times, but by 1972 only four major transatlantic liners remained in service -- the Queen Elizabeth 2 of the Cunard Line, the Michelangelo and Raffaello of the Italian Line and the French Line's France, according to the Greatoceanliners.net Web site, compiled by two young Swedish ocean liner enthusiasts, Daniel Othfors and Henrik Ljungstrom.

The birth date for the cruise industry as it exists today is generally agreed to be 1970 -- in that year 500,000 people took a cruise. The liner as transportation was clearly over. But after the luxurious France made its final ocean crossing in 1974, it wasn't abandoned entirely. It was bought by a Norwegian cruise entrepreneur, refitted and renamed the Norway; in 1979 the ship sailed for Miami to join the Norwegian Caribbean Lines as a cruise ship.

But even cruises have had to bend to the demands of modern North American vacationers who, travel statistics show, take more frequent but shorter vacations than ever before. According to CLIA, from 1983 through 1991 there was a steady decline in the length of cruise vacations -- a reflection of more capacity being added in the short-cruise market. The average cruise today lasts seven days, but the percentage of passengers taking two- to five-day cruises rose from 29.6 percent of all passengers in 1981 to 32.9 percent in 2003. There were higher peak years, though: In 2001 the percentage of short-timers was 37.2 percent; in 1994, 38 percent.

Meanwhile, the overall number of passengers increased, so the number of passengers on those short cruises actually jumped 677.5 percent, CLIA says.

Adding Home Ports

Helping the industry grow are the vast array of shipboard activities, from spa treatments to aerobics to classes and shopping arcades; the growing number of excursions, which can set a passenger back as much as $400 a pop; the freer cruise lifestyle, with cafes and casual dining spots in addition to the formal dining room; and extensive children's programs.

CLIA says 9.52 million travelers, 1 million of them children, took a cruise in 2003, a jump of 10.2 percent over the previous year. The association expects 10.6 million cruisers in 2004.

And since 2000, the number of ships on the water has increased by 41 percent, according to the group.

While cruise lines took a hit along with the rest of the travel industry after the Sept. 11, 2001, terrorist attacks, it was one of the areas quickest to recover.

One element that helped it back was the notion of "home ports," industry analysts say.

Over the past several years, more than 30 ports, from Galveston to Baltimore, have begun accepting cruise ships, meaning vacationers -- especially those who suddenly feared flying or found it a hassle -- no longer had to get to Miami or New York or Los Angeles just to get to the ship. Home ports have also helped keep the price of cruise vacations down.

"It brought cruising to your back yard," CLIA's Dale said.

It also brought keener competition. There seems to be little that one cruise line features that the others don't rush out to emulate. Want to gamble? The liners all seem to have casinos. Need pampering? They go by many different names, but spa facilities are everywhere. Some of the more ambitious installations -- elaborate water slides, for instance -- require more investment of time and money to replicate, so there may be lag time between one line's innovation and the other lines' adaptation.

But don't be surprised to see Royal Caribbean's signature rock-climbing wall, someday soon, on a cruise ship near you.

The rock-climbing wall on Explorer of the Seas, a Royal Caribbean ship that also has an ice-skating rink, golf simulators and a full-size basketball court. Carnival Cruise Lines ships feature hot tubs and yoga classes. Guests aboard the new Carnival Miracle dance in the Frankenstein's Lab disco. Royal Caribbean offers in-line skating. (The giant golf ball is actually a TV antenna.) Carnival Miracle features a water slide on the aft deck of the 960-foot liner.