Here's a random list of things you can expect to occur on Yacht Week, the sailing holiday popular with the world's moneyed youth, and described in the Croatian national press as "Sodom and Gomorrah at sea".

You will watch someone almost fall off a boat, drunk, into the sea, but recover at the last minute. You will watch someone not recover at the last minute and fall off a boat, drunk, into the sea. You will see rich men throwing themselves into the water, before realising their money is still in their pockets, and hurriedly doggy-paddling after hundreds of dollars slowly escaping in the tide. You'll see drinking games, champagne showers, stripping, island rampages, selfie sticks held up like glow sticks, spirit bottles worth hundreds of dollars delivered on silver service with fireworks strapped to the necks, and people spending the average year's salary just by slurring the word "again!" You may see - as I did - more than 40 people scramble onto a yacht meant for six for an impromptu all-night boat party, which, after a certain amount of vodka, feels more like a real-life game of Screwball Scramble. You may see - as I did - an Australian girl so drunk she keeps kissing two men on the same night under the impression they are the same person, and not understanding why this person is getting so upset, and in different voices.

Nearly everyone is beautiful, single, uninhibited, and bottle-service wealthy. Several have been on reality-TV shows. It is the only holiday you can go on, I discover, that includes two staff photographers taking pictures of everything you, the hard-partying customer, get up to at all times.

© Fabian Webster

I joined the Yacht Week for its "black route" - one that sails around the exclusive islands of Croatia, on the Adriatic - to see just why it's become such a phenomenon. The idea, after all, is fairly straightforward. You join an armada of yachts - up to 50 on any one route - after selecting your yacht-mates, booking a skipper, and even arranging an on-board chef if your budget will stretch that far (nearly all do). While on board, you drink and eat and sunbathe, and then party at every island you dock at, mostly at special Yacht Week events. It's Club 18-30, essentially, for people far too rich and glamorous to go on Club 18-30 holidays. The bigger Yacht Week has become (it started in 2008, and now has 45 routes across six countries, mostly in Europe, with plans to expand into South America and beyond) the more controversial it has been. The island of Hvar on this week's route, for instance, has increasingly become known as the new Saint-Tropez, with the mega-yachts lining its harbour belonging to everyone from Roman Abramovich and Bill Gates to Beyoncé and Tom Cruise.

Perhaps understandably, residents and guests haven't been too keen on "Hvarday", when the Yacht Week horde descends for perhaps the most raucous parties of the week (the notorious afternoon party scheduled at Carpe Diem bar sees champagne bottles worth hundreds of dollars sprayed like fire extinguishers). Just a few hours of "Hvarday" are said to be worth around £40,000 for the owners. The Hvar town council has repeatedly voted for Yacht Week's banishment, citing noise and drunken abuse; some claimed people were vomiting into the water and passing out drunk on the boardwalk. The diners next door at Gariful, Hvar's most exclusive fish restaurant, one of

Giorgio Armani's favourite haunts, were said to be less than impressed. Yet, each time, Hvar's mayor has reached a compromise with Yacht Week's founders. And so, as with every year since it began in 2008, Yacht Week sails again.

At the marina, a short drive from Split airport, I meet our skipper for the week, Sebastian, a fastidious Spaniard almost certainly given to us to show how serious about safety they are, and who chides every error (you're required to help out when docking) like a father telling his son not to murder any more prostitutes ("It can never happen again"). The other members of HMS GQ are Charlotte, an easygoing Dane who will be our chef for the week, and the GQ photographer Rebecca. We are not the typical crew. Even the smallest yachts, like ours, sleep six - making ours the only boat not at capacity.

Part of Yacht Week's appeal, it turns out, comes with selecting your boat mates. Each yacht is required to be a strict 50-50 split in gender. The majority of people I spoke to found their remaining shipmates via the "CrewFinder" section on the website, which is essentially Yacht Week's version of Tinder, and which mostly sees men advertising the remaining female spaces on a yacht they've reserved. "We are calling our boat Noah's Ark cause it is going to be filled with Animals!!!" reads a typical ad. "Looking for 4 more beer-chugging, shot-taking, pirate-costume-wearing, no f***s about what anybody is caring girls to join in the mayhem!"

Nearly all the men list their Instagram accounts for the girls to check out.

© Fabian Webster

"It's like The Real World!" a Californian blonde named Amy explains to me, referring to the American reality-TV show, but also, one presumes, the real world.

Many go purely on emails and images. Only one girl I met on my week - Cayla, a 29-year-old American teacher - took the precaution of travelling to New York to size up their potential male shipmates before she and her cousin took the plunge. "We ended up having a really boozy lunch - it was great!"

Cayla, who like nearly all on Yacht Week is single, rules out sex with her boat mates, "but we totally support bringing other people back to the boat and getting the job done."

Being a skipper on Yacht Week also has its difficulties, Sebastian informs me as we set sail. A fortnight ago, he had eleven Spaniards who barely slept, and he recalls the experience much like the sole survivor of an ethnic cleansing. Brazilian men, most skippers agree, are the worst (many mistreat female staff; a recent group got kicked off their boat for doing coke on deck).

Australians, the loudest. Americans, the most dressed in their own flag.

Skippers have an ongoing game called "Worst Question At The Worst Time". Favourites include: requesting a fry-up in a storm (oil is not your friend), trying to chat up a skipper while he's navigating a tricky mooring (most skippers are men), and having sex while you're supposed to help downing anchor.

© Marcus Olssen

After only a few hours, we arrive at Milna on the island of Brac, and I come across some guys from a mostly Dutch boat drinking with their skipper, an American man known as Cowboy Carl on account of the fact no one has seen him without his trademark cowboy hat for more than a year ("I did see him without it once," Sebastian tells me, "but I didn't recognise him").

It's around 6pm, but they already look very drunk. "They started with two bottles of vodka," says Cowboy Carl, almost misty-eyed. "And they've nearly finished them!" He hugs them. "My boys!" Carl has done 48 Yacht Week runs, and his ambition is to get to 52 to make a full year.

The opening night of Yacht Week is fairly tame, and so simply consists of a welcome open-air party in the relics of an old building involving pole dancers, light shows, vodka shots and some mild grinding. It's on this night I meet Tribble Reese. Reese is a child's idea of an American male as drawn hurriedly in crayon. He is a huge man with a jutting jaw, perfect teeth, blond hair that points to the sky, piercing eyes that would be devastating if not for the fact they're slightly too close-set, and has the nervous gregariousness of a man who has high-fived during sex. A former high-school quarterback from Atlanta, Georgia, who never quite made the grade to go pro, Reese is semi-famous in America for being the star of a reality TV dating show called Sweet Home Alabama. He was named South Carolina's Most Eligible Bachelor by Cosmopolitan in 2008.

At 29, however, he remains a bachelor, which is why he is at Yacht Week. He's out, he says, to have the experience of a lifetime - and rack up the numbers. "Nobody knows about this in the States," he tells me, excitedly, if not exactly accurately (there are more Americans here than any other nationality). "It's like the Bahamas on steroids!" Currently, Reese is most agitated by the female attention the skippers are getting. "So now I just want to be a skipper. They get laid like crazy." (The skippers, it should be said, deny this, but then of course they would. "I've had girls try to jump me," says William Wenkel, the CEO, co-founder and former skipper himself. "But I've never used my power.")

If the average age of the people who go on 18-30 holidays is early twenties, then, at 29, Reese is the average Yacht Weeker.

Take your pick from any number of reasons: a generation marrying later, an international moneyed elite looking for a wilder time, or simply the 18-30s holiday finally going high-end via the addition of boats (docking at a different port each night, after all, allows the Yacht Week to visit high-end hot-spots not yet touched by beer-boy tourism, while also promising the allure of adventure, despite that adventure coming with a timetable and personal chefs).

There are other benefits, as Reese would attest. As we set sail the next day, where your boat docks becomes the subject of much discussion. Put another way: you want to dock next to the people you got chatting to the night before. In some cases, this simply leads to jealously. In others, bribery.

Just last week, Cowboy Carl skippered a boat with many beautiful Brazilian girls on board, and found himself the subject of offers from other boats, asking them to dock next to them. "You will always meet someone you fancy," says Wenkel, "and the lubricator is the boat."

Or, more exactly, the dock. As we set sail on the second day, it becomes clear that most days follow a similar pattern on Yacht Week. Up, breakfast, leave dock, sail, stop at a cove, swim off your hangover, lunch, then sail again to that night's destination.

Eat. Party. Repeat.

Each swimming stop-off (which isn't so much about swimming as drinking on inflatables) is designed for two reasons: to socialise with other Yacht Weekers in swimwear, and to have social-media pictures taken of you while you do so. "I'm so drunk I've forgotten how to swim!" shouts one Australian man, who takes a brief pause from pretend-drowning to flirt with the real thing as he tries to wave at the photographer taking a picture of him. The two photographers who accompany every Yacht Week run, co-founder Erik Björklund later tells me, were there pretty much from Yacht Week's inception. Indeed, they're the reason for Yacht Week's phenomenal success. Nearly everyone I spoke to said they chose Yacht Week either due to the professional pictures on Facebook their friends were tagged in, or because of the YouTube trailer, made by a director better known for music videos, which has currently been viewed more than three million times. "We were pretty tech-savvy from the beginning," says Björklund. "We wanted to grow the company [by getting] people to go, have a really good time, and then share it. That's why we put photographers at every event, and then put people in good situations on the ocean - these are the images we want to be associated with."

The "good situations" are crucial, as they work both as holiday highlights (for those who are there) and de facto photo shoots (for those who are not). The second day we stop at a beautiful cove where people dive off an overhanging jut of rock into the water below while pictures are taken. These are later filtered through to Björklund back in London, to decide what goes on Facebook. A few days later we'll take part in one of Yacht Week's most popular (and photogenic - the two are nearly always one and the same) events, which involves tethering up to 20 yachts together in a star formation while everyone jumps in the middle on their inflatables, many necking Jägermeister straight from the bottle as they do so. "It's an international cesspit!" shouts one Australian girl, approvingly, while a bearded American TV producer attempts to cause hilarity by squeezing a 4ft foam rod between his legs and some Americans attempt to dole out shots while doing doggy paddle. On this day, along with the standard two staff snappers, Yacht Week will often attach a camera to the top of one the masts, all the better to take a shot already perfectly framed by the boats - shooting aspiration in a barrel.

"The boats in star formation proves particularly popular," says Björklund, when I ask about the images that attract the most attention. "Or just a group of young, hot people." But the shots of the foam-penis man will not be uploaded. "We're after aspiration."

Those not swimming are generally Instagramming, and it is partly for this reason all boats are fitted with Wi-Fi. The last thing I hear as we untether the boats and head to our next party is an Irish voice yelling, "I can't wait to see the comments!"

© Fabian Webster

Yacht Week began life simply enough - an exclusively Swedish thing, not a holiday so much as a gathering. A group of like-minded folk, sailors all, got together in 2005 to form a small armada, sail around some Croatian islands, and have a few drinks when they got there. They got home, posted their pictures on Facebook, and, says Wenkel, "said we'd never do this again".

Then they started getting the Facebook messages. How could they come on this amazing boat holiday too? "People did this before, but it never spread. We have Facebook to thank for that. We couldn't have predicted it."

They had something else to thank, too: just as Yacht Week began, in 2008 the financial crisis hit, "which meant not as many rich guys taking yachts", meaning there were more available to rent and there was more harbour space free on the premium islands. And so it grew and grew, Facebook albums spawning Facebook albums, the rise of Instagram throwing petrol on the flames. And with it, stricter rules applied by some islands, banishment from others, tense negotiations from yet more. "And now," says Wenkel, "I have to control this little Frankenstein."

© Fabian Webster

Currently, this particular little Frankenstein's monster is taking the form of Tribble Reese, who is attempting to neck a bottle of vodka the size of a parking bollard. This is not an exaggeration. We are at a party on the island of Vis, on the top of an abandoned fort built in 1813 by the British Royal Navy, and now put to use by Yacht Week as an exclusive party locale. The DJ is spinning, hands are in the air, spirits are being downed, lanterns hang from the trees above us, and by 2am, all the ships' captains will stand in a circle, holding bottles of champagne worth several thousand dollars in total, bought by their respective passengers, to spray over the entire dance floor.

For now, the Amex black cards and MasterCard gold cards are getting a thorough flexing partly due to the bottle service - each spirit bottle arriving with some form of fireworks attached - and partly due to the sizes of the bottles being served. Hence, Reese is currently upending a six-litre bottle of Belvedere into his person. I can honestly say I never knew vodka could be purchased in quantities so huge. Having heaved it high above his head, he looks, to all intents and purposes, like a gerbil who has liberated its water bottle from the side of its cage, and is now wondering if this was such a good idea. It probably shouldn't come as a shock, however, that Reese was posing for a shot for GQ's photographer at the time. Throughout the night, he gamely heaves the bottle high above his head for any other iPhone snappers or eager Instagrammers who are interested, while directing his friends to do the same. Look how crazy he is! There is no strict evidence he drinks a single drop. "Man, I've done reality TV, so let me know what stupid quotes you need!" he tells me later. I say he's already made the piece. He looks very happy.

These survivalist-sized vodka bottles, remarkably, are standard on Yacht Week. Even more remarkably, many were bought at the marina shop on the first day to drink on board, meaning a week's worth of watching people heave up bottles with both hands in order to pour, veins pulsing in their necks, looking like firemen with high-powered hoses, and often causing vodka tsunamis when they rock from a wave. They're not exactly ideal for the high seas. Yet almost every time someone pours, someone Instagrams. Just look how big they are! Imagine the comments.

© Fabian Webster

It stands to reason, perhaps, that a holiday born from Facebook jealousy and spirited by social-media word of mouth should attract people keen to pass the envy baton along, and show their own friends what a good time they've also had ("I think self-expression is really important for a lot of young people," says Björklund, by way of explanation. "When you have these experiences, you want to share them").

But there are other, more curious, things about Yacht Week. Take the parties. Nearly all the venues are actually tiered amphitheatres. At the party on top of the abandoned Fort George, for instance, the dance floor is actually sunken, with three levels ringing around above it, meaning, in practice, everyone is on display to everyone else at all times, but often too separated, by distance and depth, to talk to anyone they don't already know (pick the social-media metaphor out of that). It also resulted in the most curious sight of the night: half the people on the upper levels facing away from the actual party at any one time as they attempted to take selfies with the dance floor in the background, but looking, from a distance, like Manchester City fans doing the Poznan, or dissidents enacting some form of political protest.

This tiering has other uses too. When I joined the notorious afternoon blowout - and cause of so many complaints - at Carpe Diem bar on Hvar island later in the week, as House Of Pain's "Jump Around" boomed from the sound system, the multi-levels that spanned 360° around the main dance floor were being used by those spraying the champagne, and all the better to get pictured while doing it too.

© Marcus Olssen

While being expensively drenched, I get talking to Benjamin, a 29-year-old hedge-fund manager from Chicago. Last night, he says, he and three friends spent $40,000 on champagne. He still owes his friend his $10,000 share, "as the island didn't take Amex!"

Yesterday, after docking, everyone in the boats nearby immediately emptied their pockets and jumped into the water for a refreshing swim. Walking along the pier afterwards to dry himself off, "I walked along the dock, and you'd see seven Amex black cards, six Rolex watches... everything you can imagine. It's insane."

Last month, says Charlotte, GQ's on-board cook, she remembers watching hundreds of dollars float past in the water, followed by a wallet, following by a frantically paddling American who asked, "Have you seen a Gold Mastercard float this way?" "They're either rich or mommy and daddy are," says Julian Brockburst, a skipper. "But it's more than a holiday. As a networking event, it's unbeatable."

Last year, he says, an entrepreneur passed him his card, "and I'm now doing coding for him!" (He had never done coding before).

Another person, he says, recommended he buy shares in e-cigarettes when they were just $1. He didn't. "And now they're $14! But all these guys, they're masters and MDMAs." (He means MBAs - people possessing master's degrees in business administration - rather than people possessing the illegal compound of ecstasy.)

But on this evening, the champagne sprayers aren't just being recorded by others - many are recording themselves. At least three people in the writhing, jumping crowd have selfie sticks held aloft with GoPro cameras attached. It turns out they're recording footage for "YouTube trailers" of their own holidays, which they record every day, and which they'll later professionally edit, set to music and upload - or get someone else to do it for them.

So popular, in fact, Björklund tells me later, they're integrating them with the official Yacht Week website. They've recently set up a new section called "Yacht Week Independent" where they highlight the best.

These things will happen before Yacht Week ends.

Reese - after striking out for four days in a row, virtually unheard of at Yacht Week - finally gets laid. He will run up and high-five me with this news. More incredibly expensive champagne will be sprayed, of which a New Zealand girl, Sian, will later write on her blog: "$100 bottles of champagne being sprayed over the crowd seems like something just from the movies, not for us!"

We will go to a party on a private island that does feel like a movie. We will get there on a water taxi, arriving at what feels like the most exclusive festival in the world, with the beautiful super-yacht rich in attendance; we will raise our hands in the air as the DJ plays, and the trees sway, and see others with their arms outstretched too, holding selfie sticks to the sky for the best angle possible, the night of their lives already self-fulfilled.

Months later, Tribble Reese will email me. Yacht Week changed his life, he says. He's spent the past few months sailing around the world with a skipper he met there. His cook, randomly enough, is Charlotte - the same patient, easygoing Dane who fed HMS GQ so well. They're currently in the Caribbean, and plan to head for the British Virgin Islands to join the Yacht Week armada once more. Then, on to South America, and adventure. He has a ton of cool footage, he tells me. He's making a film of it. He'd love to show it to me.