"We are safely away and you can now enjoy a..." There was a pause, as if the cruise director was having trouble choosing what, exactly, he should call what was about to happen. Finally he said, "...a carefree environment."

The announcement was still reverberating through the ship when the scrotum airing began in earnest; shorts and shirts dropped to the ground and penises dangled in the south Florida sun. Permission had been granted. Now buttocks could swing from side to side with no restrictions, and breasts – finally released from the prison of blouse and brassiere – burst into the open, to be caressed by soft tropical breezes. We were on a boat. One thousand, eight hundred and sixty-six nudists living the "anti-textile" dream.

Not that some of them weren't almost nude before the cruise director gave the all clear. Many were in various states of undress, itching to toss their clothes aside. A skeletal man in his eighties wandered around the ship wearing only a fluorescent thong, his loose skin draped around his bones in cascades that looked like freckled frosting, and a gigantic, barrel-chested man – he looked like he'd eaten an actual barrel – lumbered around the lido deck on an industrial-strength cane, wearing only a loincloth. A few people soaked in Jacuzzis, surreptitiously slipping out of their swimsuits, while the less rebellious sat by the pool, looking somewhat forlorn, waiting for the green light. These were nudists, after all. And they had paid big bucks to frolic in the buff. When the all clear was sounded, they didn't hesitate.

There are rules for being a nudist. It's not enough to drop your trousers and waggle your genitals in the sunshine. That might be fun – or, depending where you are, get you arrested – but it's not nudism. You can take off your clothes and run across a football field, but that's not nudism, that's streaking. Jump in a lake and frolic naked with several of your friends? That's skinny-dipping. Fun, but not nudism. Even bathing in a Japanese onsen isn't nudism. Yes, you're naked and with other naked people in a hot spring, but after you've cleaned and refreshed in the cold plunge, you get dressed and go out for ramen. A nudist would eat noodles naked, with other naked people.

Nudists enjoy life on the ocean wave (Alamy)

Various groups have different agendas and interpretations, but they all pretty much agree that nudism is a social activity. If you're alone, you're just naked, but if you are in a mixed group of men and women engaged in the conscious practice of standing around in the buff, then you are a nudist practising nudism.

I had never been on a cruise ship before – I'd never even been interested in being on a cruise ship – but this wasn't just any cruise, this was the Big Nude Boat, a special charter offered by Bare Necessities, the premier "nakation" (a portmanteau of "naked" and "vacation," but you probably figured that out) travel agency. Not only that, the cruise was on board the Nieuw Amsterdam, one of the Holland America Line's more luxurious ships, which meant this was the deluxe version of non-sexual social nude recreation. Meaning nudism. Or naturism. Depending on who you ask. There are several theories floating around about which word means what – historically speaking there are some actual distinctions – but the reality was that I was on a boat with almost 2,000 people who weren't wearing clothes.

I am fascinated by subcultures: the Deadheads and Juggalos who have built unique cultures out of following their favourite bands as they tour the country, the amateur mechanical engineers who build robots in their garages, the home brewers who experiment with beer in their kitchens and the foodies who eat at illegal restaurants in people's homes. People do strange things. They collect stamps and watch trains, they dress their pets to look like famous characters from movies, they dress themselves to look like anime characters, they go to conventions in woodland animal costumes and have group sex in "plushie piles".

All of these activities have their own culture, a network of people who speak a specific kind of lingo that outsiders don't understand. I'm especially fascinated by subcultures that are deemed morally suspect or quasi-legal: the people who pursue their passion even if it means possible imprisonment or stigmatisation by society. I can't help it. I like the true believers. The fanatics.

My first nonfiction book was about cannabis connoisseurs and the underground botanists who source heirloom varietals of marijuana from all over the world. Cannabis culture has a rich history, filled with colourful characters. These are men and women who defy oppressive anti-drug laws and good-naturedly don't give a fuck about societal norms. It wasn't much of a leap for me to become intrigued by the world of nudism. Or as my wife said: "First you're stoned all the time and now you're going to be naked? Why can't you write a book about cheese? You like cheese."

If you're alone, you're just naked, but if you are in a group standing around in the buff, then you are a nudist (AFP/Getty)

The loudspeaker on the ship crackled to life and the cruise director added a caveat: "I would like to remind you that you must wear a cover-up in the dining areas." Which didn't really keep anyone from being naked in the dining areas. Or in the bars. Or anywhere for that matter. They were naked on deck and in the screening room, the library, the casino and the buffet line. Nudists crowded around the piano bar and requested songs by Elton John and Billy Joel. The large theatre where stage shows were presented was filled with naked men and women. They were in the elevators, walking down the corridors, playing ping pong, lifting weights in the gym, and guzzling cocktails by the pool.

In the fitness centre someone asked the ship's in-house yoga teacher if people had to wear clothes in the yoga classes. The teacher gave her a curious look and then, as the true reality of the question sunk in – what I can only imagine was the image of a roomful of naked people doing downward-facing-dog flashing through her head – her face bloomed in panic and she said: "Oh yeah. In the class. Clothes. You have to wear clothes."

But other than the yoga class, everywhere you looked, testicles and breasts hung low and pendulous, swaying side to side as the boat rocked in the open ocean; billows of bulbous flesh spilling off torsos, flowing earthward like the goop inside a lava lamp. The entire human body presented in all its natural nature was unavoidably on display.

I was sitting at what was called the Ocean Bar that first evening when I overheard a man, a silver-haired smoothy, complain loudly that there were too many old people on the cruise. "I'm guessing the median age is 65," he said. He was 62. When old people complain that there are too many old people, then you really know there are too many old people. Most of the passengers were retirees and most of them were American. Which is to say that there were a lot of overweight people strutting around in their birthday suits.

That they did so unselfconsciously, without any hint of the neurotic body obsession that has created generations of diet-obsessed, bulimic, anorexic or just plain miserable people, was something that I found almost inspirational. They weren't ashamed of their bodies, they seemed to accept themselves and one another for who they are and what they were and, best of all, they had fun doing it.

Not all of them were retired. I met a Harvard professor, a radiologist, a tool salesman and a couple of people serving in the armed forces. There were pharmaceutical sales reps, retail clerks, photographers, scientists, doctors, corporate executives, teachers, lawyers, paralegals and people who really didn't want to talk about work while they were on holiday.

And of course not everyone was fat and saggy. There was a large LGBT contingent who were on the healthy end of the body mass index, and there were some actual bona fide young people, trim and tattooed men and women in their twenties who clung together as if the naked retirees were harbingers of some sort of terrifying apocalypse. The naked twentysomethings gazed at the naked seventysomethings as if they could suddenly see the future, like a portal had opened in the space-time continuum and revealed a dystopian world where gravity and a sedentary lifestyle conspired to make everyone expand and sag. It was heartbreakingly inevitable. Perhaps this glimpse into the abyss explained some of the uninhibited alcohol consumption among the younger set.

The guests on the nude cruise were for the most part Caucasian, although there were a few South Asians, East Asians, and African-Americans in the clothes-free contingent. They came from all over the US and Europe, too: Canadians from Toronto and Quebec, and people from Finland, Australia, Germany and the Netherlands. All these people, coming for the express purpose of standing around on the lido deck of a cruise ship and letting it all hang out.

As I was standing naked in front of these people, I have to say that I didn't feel a sudden sense of liberation. But I didn't feel afraid or ashamed either. My self-esteem didn't increase or decrease. Mostly I felt a little awkward. I've never talked to a naked stranger while being naked before and I was unsure what to say. Like, how was I supposed to greet people? Would my saying hello be interpreted as overt sexual behaviour? And what were they thinking about me? Did I appear unhealthily pale? An obvious first-timer? Nudists refer to people with untanned buttocks as "cottontails". I'll be the first to admit my ass doesn't see a lot of sunlight. Were they all scoffing and muttering "cottontail" under their breath?

I noticed that a couple of the women were violating one of the unspoken rules of nudism – "don't gawk". They were staring at me, their eyes wide.

I quickly realised why. It was not my physique or lack of tan that was making them goggle; it was the fact that my penis had become incredibly shiny in the sunlight. The spray-on sunblock that I had so scrupulously and thickly applied had turned my dick into something resembling a solar flare. I could've sent a distress signal to a search and rescue team.

I swam a little. I read a book. I watched a youngish woman with a flower tattooed on her bum walk to the bar and fetch a couple of drinks. I was enjoying non-sexual social nudism. I sat in my chair by the pool. Was this a more enjoyable experience than sitting by a pool and reading with a swimsuit on?

If I'm honest, I have to admit that it was. It felt good to let the sun and the warm desert breeze dry my skin after a dip in the water without the feeling of clammy fabric sticking to my body. Admittedly, it was strange to look around and see naked people, but they were doing a pretty standard version of what people on vacation do, reading or snoozing or drinking cocktails and laughing – all in a non-sexual way, naturally. Nobody gawked, nobody said anything offensive or racy, it was all very proper.

I suppose, for me, it was a bit too proper. But after a while I got used to it. I didn't feel weird or embarrassed or uncomfortable being naked around these people, and the few who would dare talk to a lone naked man were totally friendly.

There was nothing else to do but kick back and relax, so I laid out on the chaise longue, my penis reflecting the sun like a chunk of fool's gold.