It's almost a contradiction: the "short cruise." Cruises are supposed to be long and leisurely, unending escapes on slow boats to relaxation and maybe even romance. But not everybody has time for the lengthy pursuit of pleasure, a fact of which the cruise-line trade is very much aware. A half-dozen or so lines, most of them sailing out of Miami, have condensed the standard one-week Caribbean interlude into a fast-paced three- and four-day fling.

How fast?

Brian Blackford, cruise director of the Norwegian Caribbean Lines' Sunward II, briefed the 500 or so newly boarded passengers embarking on a three-night, 64-hour weekend cruise from Miami to Nassau in the Bahamas early last month:

Passengers on a week-long cruise have lots of opportunities to get to know one another, explained Blackford, a plump Australian whose job, essentially, is to be the life of the party. But time is more precious on the Sunward II's twice weekly "Bahamarama" cruises, and if you want to meet someone new, you have to move fast.


"Take a good look around you," he urged his audience, even before the luxury liner left the dock in Miami. "Now jump up, run over and hug somebody."

The last few years (and especially 1984) have seen a surge of large luxury liners entering the short-cruise market, something of a phenomenon in the industry.

On most Friday afternoons year-round, at least four large passenger ships set sail on a three-night round trip to Nassau. On Mondays, they depart for Nassau and Freeport in the Bahamas for an alternative four-night cruise.

They are Norwegian Caribbean Lines' Sunward II (674 passengers); Carnival Cruise Lines' Carnivale (950); Dolphin Cruise Line's Dolphin IV (566); and Eastern Cruise Lines' SS Emerald Seas (1,000).

Two other Nassau-bound short cruises, with slightly different itineraries, are Premier Cruise Lines' Royale (772), departing Port Canaveral, north of Miami, on Fridays for three nights and Mondays for four nights; and Fantasy Cruises' Galileo (1,200), sailing Fridays from Miami for Nassau for only two nights. (The rest of the week, the Galileo heads for Key West and Mexico's Cozumel for five nights.)

On the West Coast, Western Cruise Lines' Azure Seas (740) sails Fridays from Los Angeles for Ensenada, Mexico, on a three-night round trip. Its four-nighters depart Mondays for San Diego and Ensenada.

Off they go twice-weekly, giving passengers at least a taste of what the cruising life is about. Though itineraries are similar, the ships have their differences. The smaller Dolphin boasts of its intimacy, the huge Carnivale of its many entertainment facilities. The Emerald Seas claims "the roomiest staterooms afloat."

Several of the ships -- the Sunward II, Emerald Seas, Dolphin IV and Royale -- anchor off a Bahamas out island, treating their passengers to an afternoon at a private beach. The Carnivale, on the other hand, capitalizes on its one indoor and four outdoor swimming pools, advertising "a full day at sea" instead of in another port.

The emphasis is definitely on good times. Carnival has dubbed itself the "fun ship" line. Boarding passengers on the Norwegian Caribbean's Sunward II are told the crew is present to assure them of "fun." Its "number-one goal," says Premier's Royale, "is to make sure everyone has fun."

It all sounds a bit frantic, which may be exactly what you want. But quieter souls can find cozy corners on deck to nap, explore Nassau on their own, dip briefly into the ship's social life and disappear into the privacy of their cabins well before the disco crowd really gets moving.

What accounts for the growing popularity of these abbreviated holidays?

For one thing, they are much cheaper than longer cruises. When a per-person berth aboard a liner sells for $100 to $200, and up, a night, the shorter the cruise, the less you have to pay. Most lines also arrange for a substantially reduced round-trip air fare for passengers.

For another, a weekend getaway in the pampered comfort of a floating resort appeals to a lot of people pressed for time who might not otherwise consider a longer cruise. "For many people," says Western Cruise Lines, "three- and four-night mini-vacations are a way of life."

The cruise lines themselves see the short cruise as an introduction to sailing for the first-time passenger. Says Carnival vice president Bob Dickenson:

"He can get his feet wet, so to speak, over an easy, all-inclusive weekend. And once he has had that experience, we are confident he will be ready for a full seven days." The idea is to turn "the cruise novice into a cruise fanatic."

A number of travelers, it seems, are adding quickie cruises to a longer vacation in Florida (or Southern California), and some of the lines -- Premier, particularly -- offer add-on packages to Disney World in Orlando and other attractions to fill a week.

Surprisingly, the Florida sailings are drawing passengers not only from the East Coast but from all over the United States. Carnival Lines' heaviest traffic, its statistics show, comes from Dallas, St. Louis, Chicago and New York.

Sunward II's first three-day cruise of 1985 attracted a group of about 30 holidaying Brigham Young University students from Provo, Utah, and an older couple from Reno, Nev. The idea, they said, of even a short winter break from snow at home to a tropical sun and sea appealed to them.

At least once on every mini-cruise, short as they are, you do get a chance to plunge into a warm surf.

Yes, but on a hurry-up cruise, what do travelers lose?

Hardly anything, it seems, except maybe unplanned hours simply to relax by the rail and watch the play of the waves.

The Sunward II's three-night cruise is a good example. The entertainment staff seems intent on cramming into the time available as many traditional sailing experiences as any good-times-hungry passenger can manage.

As you step aboard, they hand you a legal-size sheet of paper filled with activities, and that's only for the first evening. There's a new sheet slipped under the cabin door for every day.

On the full weekend agenda are:

Two ports; two nightclub shows; two nights of casino gambling; 11 full meals (breakfast, lunch, dinner, midnight buffet) plus assorted between-meal snacks; disco dancing; aerobic stretching exercises; sightseeing excursions; a couple of good movies (a James Bond thriller); a beach picnic on a private island; snorkeling lessons; and (very traditional) trap-shooting from the stern under the watchful eye of a ship's officer.

On the second night out, the captain throws his welcoming cocktail party (free champagne), a very dressy affair (a few tuxes and ballgowns in the crowd). He shakes hands in a reception line, makes a little speech and on this evening only dines with the passengers, inviting a half-dozen couples to join him and the rest of the officers at the captain's table.

And then, just one night later, you are attending the gala farewell dinner party. Balloons drape from the dining room ceiling; everybody gets a party hat; and when dessert time comes, the lights dim and the serving staff dances in holding aloft trays of flaming baked Alaska. Yesterday you were saying hello to your table mates; tonight you are making your goodbyes.

There's so much to keep busy at on this cruise, you can almost miss the ocean outside.

Late Sunday afternoon on a recent cruise, as the Sunward II pulled away from Great Stirrup Cay, where it had anchored for the beach picnic, the sunset was so gorgeous the captain was inspired to make a public-address announcement, urging everyone to go on deck and have a look.

Homeward-bound, the ship was pointed directly into the sun, a dazzling orange ball trimmed in pinks and purples. As the sun began to disappear, up from the eastern horizon sprang a full moon, casting its sparkling rays across the ship's wake. Together, they produced as lovely a seascape as any ancient mariner could ever have hoped to enjoy.

But only a few of the Sunward II's passengers saw it. Most of them, ignoring the captain's advice, had been lured to the Bahamarama Lounge for Jackpot Bingo. "Fun and cash prizes" at 4:45 p.m.

Too bad. On a short cruise, you don't get that many sunsets.

A getaway cruise goes like clockwork. It has to; there's no time for delays.

Typically, passengers fly into Miami sometime Friday morning or early afternoon. At the airport, a fleet of buses waits to transport them directly to the dock, stopping at each of the several ships.

The Sunward II sails at 4:30 p.m., and passengers must be on board by 4 p.m. At the dock, a porter takes the luggage. It will be delivered to the cabin door while you are checking in.

Before you even step on ship, a wine steward asks your choice of wine for dinner. Of course you don't have to make up your mind immediately, but if you wait until dinnertime, the stewards may have so many people to serve at once they won't get around to you until mid-meal.

On board, your first goal is to locate your cabin, and then you begin to pay heed to the repeated announcements over the public-address system.

Time, already, to sign up for snorkeling lessons and Saturday's tours of Nassau, it informs. Time, also, to arrange for credit, so you can sign for drinks at the bar. Time, finally -- all the registration chores completed -- for late lunch, a picnic snack served all afternoon around the outdoor swimming pool.

The Sunward II has nine passenger decks, and you begin to think, as you search out the bars and theaters, that it's going to take all three days aboard to find your way around.

At 4:15, lifeboat drill. At 4:30, the ship's whistles blow, and the Sunward II eases away from its pier, Nassau-bound. Another liner is just ahead; a third will follow shortly. You will see them, now and again, throughout the weekend. They are a pretty sight at night, lights aglow in the distance. If the ship sinks, you think, help is near.

Why are they all headed for Nassau? For a short cruise out of Miami, says the Sunward's Norwegian master, Jens Hansen, it is the most convenient port. He thinks, with a Scandinavian sense of orderliness, that with so many ships arriving weekly, perhaps Nassau could spruce itself up a bit.

As Miami disappears and nightfall approaches, you glance at the schedule: Beginning immediately, "Bon Voyage Music" with the "Calypso Playboys." No time wasted getting things going here. If you want a party, it's just begun. If not, you can stroll the deck or rest from the flight south in your cabin. Dinner at 6 or 8 and a live music and comedy show to follow.

Night One the Sunward II sails to Nassau, anchoring before breakfast on Saturday. It spends the next 24 hours in port. The day is free for sightseeing and swimming and a visit on Night Two to the gambling tables on adjacent Paradise Island.

Sunday at dawn, the Sunward II glides quietly out of Nassau bound for Great Stirrup Cay, a tiny island about five hours distant. Early birds can grab a cup of wake-up coffee by the pool for a last look at Nassau.

After breakfast, the exercise classes go into full swing, but this is the best time to find a deck chair and read while sea breezes rumple your hair.

Great Stirrup Cay, when you arrive, is a lark. If you have never been on a tropical isle, this is what Hollywood has led you to hope for. A calypso band plays beneath the thatched roof of a little grass hut. Another grass hut dispenses rum punches.

Several cruise lines have acquired small islands, where passengers have exclusive use of the beach for a few hours. All afternoon, a launch shuttles between ship and shore, so you can stay as long or as briefly as you want. Emerald Seas anchors not far from the Sunward II, shuttling its passengers to neighboring Little Stirrup Cay.

At lunch, the kitchen staff is ferried over to serve hamburgers and hot dogs (not tropical, but you don't really mind after the second or third punch). The sand is white, the palms wave and the sea is clear.

And suddenly Night Three is upon you, and the voyage is almost over. The goodbye dinner, another show, the final midnight buffet; and by the time most passengers have awakened on Monday, the Sunward II will be docking again in Miami. An early breakfast is served while the ship is cleared through U.S. customs, and by 10 a.m. you are back on a bus bound for the Miami airport.

Has it been relaxing, this hectic itinerary? Possibly, if you skipped some of the activities.

Or an exhausting whirlwind? Probably, but a lot of fun, too, if that's what you were looking for.

We sailed on one of southern Florida's chilly winter weekends, and Nassau wasn't much warmer. I never saw anybody dive into the ship's swimming pool. Too nippy. People were disappointed by the weather, but they didn't complain. They had a lot of other things to do.

It is hard to consider Nassau a foreign port. The people speak English; the shops take U.S. dollars readily; and when a half-dozen ships each disgorge hundreds of passengers at the same time, you think you are in a busy American shopping mall. Still, a new place teases the curiosity, and we spent the day exploring.

We rode in a horse-drawn surrey through the city streets (romantic); visited the famous Straw Market (quaint) and shopped for bargains (practical). We have a set of Waterford crystal and replaced last year's breakage at a saving of about $15 per glass.

The captain was right: Nassau is a bit scruffy (at least compared to Oslo), but hardly worse than many other tropical capitals.

On Sunday, temperatures rose, and by the time we reached Great Stirrup Cay, the hardiest of the passengers put on bikinis to sun and to swim. The truth is that the water was much warmer than the air. Once you plunged in, you could float indefinitely in what felt like a heated pool.

In mid-winter, just one chance to splash in a tropical sea is enough to make the cruise a success. That's what I remember most.

That and the colors: That last night's orange and purple sunset and the sea itself, always changing. Aquamarine, emerald green, royal blue, purple black and softer, again, to robin's-egg blue.

Funny thing, at the final dinner I even felt sad about saying goodbye to our table mates, though we had barely come to know them: the older couple from Reno; a younger pair from Roanoke, Va.; and a West German business student on a semester break from Houston, joined by his affable father from Frankfurt.

Yet in each day's rush, we had met for breakfast and for dinner, exchanging accounts of our various activities. They had become, in a sense, our family on ship, proof that you can make friends even when time is short.

The cruise lines certainly know what they are doing. Give the passengers a taste of good times, and many of them will be eager to sail again, next time on a longer voyage. Maybe around the world?