The night before the Carnival Imagination was to set sail on a four-day Labor Day cruise from Miami to Key West and Cozumel, Mexico, the 233 people who had signed up for the organized "singles cruise," part of the general 2,000-passenger cruise population, were invited to a pre-sail cocktail party at a lounge in the city.

I walked in alone feeling like a nervous freshman on the first day of school, except that the crowd ranged in age from the 20s to the 70s and was in full schmooze mode. A loud "whoo!" erupted as a group of fifty-somethings did shots at the bar.

"Where are your beads?" asked a gregarious woman with a mojito and a thick New Jersey accent. A beaded necklace that spelled "Angela" rested in her cleavage, where she also kept her money and phone.

The name beads, I soon discovered, are the singles cruiser's most important accessory. They are an automatic friend finder, a green light that it is safe to approach.

Angela, who that day was celebrating her 55th birthday, told me she was divorced and booked the singles cruise to be around "positive people."

"If you're not having fun, you haven't tried," she hollered over the thumping music.

We worked the room together, meeting the universally friendly folks with whom we would spend the next four days in an 855-foot-long party boat. One of them was a 68-year-old gentleman, twice my age.

"I'm here to have fun; if I get lucky, it's a bonus," he said with a wink, expressing a mantra I would hear pretty much everyone repeat.

And so began the fascinating anthropological experiment that is a singles cruise, where people meet for nonstop speed dating in a hotel you can't escape.

That sounds horrifying, I realize — but, somehow, it was fun.

"Cruise goggles" make everyone seem more attractive after a couple of days. And for many singles tired of being the extra wheel among their married friends, Singlescruise.com's very fitting motto — "Travel single, never alone!"­ — can be a vacation savior.

"I just wanted to go away and dance with someone single if I want and not eat alone," explained David, a 54-year-old from Fort Lauderdale.

Rare romances bud

Once the Imagination had set sail, the singles gathered for an orientation mixer in the Xanadu Lounge. The Cupid Shuffle line dance got the party started. Karaoke followed. There were, thankfully, free cocktails.

A patchwork of characters soon emerged: divorcees letting loose; shy guys vying for attention; marriage-ready women scouting for mates; a group of thirty-something friends who were, it seemed, never sober.

Gathering for dinner each night at the designated singles-cruise tables in the Spirit dining room, people whose paths otherwise never would cross made small talk about their jobs and kids and how they heard about the cruise (many saw a promotion on Match.com).

It's no surprise that booze plays a starring role on a singles cruise. The organized excursion in sweat-soaked Key West was a five-bar pub crawl, starting at 9:30 a.m., following a guide who blew a conch shell when it was time for the next bar. In Cozumel, snorkeling and a tour of the botanical gardens were some of the activities at the Chankanaab National Park, but mostly people did shots at the pool's swim-up bar and then squeezed into a hut for a raucous tequila tasting.

Between Battle of the Sexes trivia and crammed hot tubs on the adults-only Serenity Deck, the rare romance began to bud. Some became serious fast.

Ron, a 41-year-old firefighter from Indianapolis, and Kaye, a 40-year-old nurse from Connecticut, first locked eyes in the baggage-claim area at Miami International Airport the day the ship departed. Less than 24 hours later, they looked like a long-term couple who had stumbled onto the wrong cruise.

Courtship in a floating cocoon can be bizarrely accelerated. A pleasant chat poolside can lead to a daylong frolic, then dinner, then dancing, then a midnight kiss at the ship's bow, then a heart-to-heart about whether he wants more kids and whether she'll travel to visit, all 12 hours in.

The bubble often bursts when reality hits. But sometimes the safety of the bubble opens your mind.

A 33-year-old Miami interior designer was surprised to see her feelings evolve for a 59-year-old research pharmacist who lives in Washington, D.C. The close quarters allowed them to focus on getting to know each other without "real life" distractions, and she put aside her concern about the age gap.

Three months later, they still were dating long distance.

Mustard on a wedding dress

Cruise director Shelby Bergeron said that over the past seven years with the company, she has been notified of at least a dozen marriages and two babies that have resulted from Singlescruise.com's events. Less officially, another of the cruise directors gave me this breakdown from his observations: About 85 percent of cruisers meet someone they connect with; 35 percent become romantic; 18 percent promise to keep in touch; 7 percent actually see each other again on land.

As some relationships formed via cruise, others were laid to rest.

On "Elegant Night," a 36-year-old Georgia woman named Christy wore her wedding dress. As dinner wound down, she invited her single peers to help her defile it with canisters of spray paint and splatters of mustard and chocolate sauce. "It was so cathartic," said Christy, who said she had been divorced for a year, longer than she was married.

On "Tropical Night" the following evening, a 46-year-old Los Angeles lighting designer named Steve showed up at the Dream Bar wearing a coconut bra and straw skirt, which wasn't all that out of character. During a dance contest earlier, he had attempted the worm.

A widower for 22 years and recently out of a "poisoned" relationship, Steve was on the cruise because his brother suggested it as a way to move on. Steve had adopted the motto "I will not be afraid" and was, truly, letting it all hang out. "This is my first singles cruise, but it will not be my last," Steve said. And the poisonous ex?

"I can't even remember her name at this point."