Cruises take passengers to some of the world's most exciting places, but there are a few secrets – both good and bad – behind the opulent décor and all-you-can-eat buffets. Here are 37 of the most surprising things you didn't know about cruises.

One of the things people love most about cruise ships is the food. Sadly, this isn’t always the case for the crew. While the crew mess will provide a range of options for breakfast, lunch and dinner, the selections are often questionable. Make-your-own-pizza day is a highlight, but goat foot curry and a platter of fish heads? Not so much.

While the crew food might be lacking, a combination of the unlimited buffet, specialty restaurants, exotic cocktails and a lack of exercise (despite the onboard gym) means most guests disembark heavier than when they arrived. According to Cruise Reviews, the average weight gain for a seven-10 day trip is five-10 lbs. There's food on offer 24/7 after all.

Don’t panic, it’s not standard practice for the cruise ship staff to check your weight every morning. However, sometimes the port excursions and tours you book in advance, such as zip line rides or paragliding, have weight restrictions for safety reasons. If you decide to go on one of these tours, don’t be surprised if you have to jump on the scales beforehand so that staff can ensure you’re under the limit.

The plumbing system on most cruise ships is temperamental, and absolutely nothing besides the specially designed paper should be put down the toilet. Unfortunately, when there is a blockage it can lead to an entire section of the ship without functioning toilets, and in the worst cases, raw sewage leaking down corridors, usually in crew areas.

If there’s an issue with the water filtration system or water starts to run low on board, you might actually get asked to avoid flushing your toilet, or to stop taking showers. It’s not something anyone can really police, so you probably won’t get in trouble if you ignore the requests, but if you want to help conserve water, you might have to put up with poor hygiene for a while.

Ross Klein’s 2008 book Paradise Lost at Sea: Rethinking Cruise Vacations cited that the carbon footprint of a cruise liner is three times greater per head than a Boeing 747. Surfrider.com reported that a ship with 3,000 passengers plus crew generates a million gallons of grey (used) water; 210,000 gallons of sewage; 100,000 gallons of toxic waste; and 50 tonnes of rubbish weekly. Cruise lines usually have internal environmental programmes, but that doesn't mean they are environmentally friendly.

A one-week voyage by a mid-sized ship generates about 210,000 gallons of "black water" (human waste). This has to be discharged at least four miles from shore, and can have a detrimental effect on sea life. Many cruise lines choose to discharge this waste much further from shore lines than the minimum four miles, but that doesn't lessen the impact on the underwater ecosystem.

Relationships between guests and crew members are strictly forbidden. This has a lot to do with potential lawsuits and historical instances of sexual harassment accusations against staff of major cruise lines. Crew are expected to be professional at all times, even if they meet a guest in port. That doesn’t mean that it doesn’t happen, but if they get caught, they’ll probably lose their job.

Crew members spend at least six months at a time living on board. Many of them will also be stationed on the same ship each time they do a contract, living in close quarters with the same group of people for extended periods. International romances between crew members are very common, and sometimes these relationships even lead to marriage. Most of the time, however, it never progresses beyond a casual hook-up. What happens at sea stays at sea...

Cruise ships are monitored by 24-hour CCTV for safety and security reasons, to protect both the crew and the guests if an incident occurs. It also means that crime rates are very low on board, so your valuables are pretty safe. Before you feel too violated, there aren't any security cameras in your cabin, so you do have some privacy.

Crime is rare, but just in case, all ships have a brig or holding cell to detain anyone caught breaking the law. There are no police on board, but security staff have police powers and the captain is the final authority until the ship docks. The next port of call determines the laws under which the offender is prosecuted, so would-be criminals should think twice before causing trouble, unless they’re OK with languishing in a foreign prison for an extended period of time.

Although you might assume ships are a tried and tested way for smugglers to deliver drugs across the world, cruise lines have very tight security and everything you take on and off the ship is scanned, just like at an airport. The coastguard will often bring trained dogs on board to sniff out anything suspicious. Because offenders are at the mercy of the authorities in the next port, and some countries carry the death penalty for drug smuggling, it’s a very risky move.

Because cruise ships are such enclosed environments, ship-wide outbreaks of vomit-inducing illness are common. Cruise companies do everything they can to prevent this, including constant cleaning and reminding everyone to wash their hands, but it doesn't take much for a “Code Red” situation to arise. If you’re no longer allowed to serve yourself at the buffet and you spot entertainers and musicians frantically cleaning the handrails, there’s a good chance norovirus is going around.

Every cruise ship has an onboard medical centre, but unfortunately there’s no NHS at sea. Most medical treatments will cost you considerably, and insurance policies can be a bit hazy on what they cover with cruising so make sure you know what you’re in for before you go. If an emergency happens, the ship will have life-saving equipment on board, but if they have to order a medical evacuation by helicopter it could end up costing you thousands of pounds.

In 2015 it was estimated that an average of around 200 people die annually on cruise ships. While this number isn't hugely significant among the millions of passengers that set sail each year, every ocean-going vessel still has to have a supply of body bags and its own morgue. It’s usually below decks and crew members have been known to run into a body when it’s on its way down. Creepy.

While the statistics for people missing overboard from ships are relatively low, solving the mystery behind their disappearance can be difficult because investigations are handled from where the ship is registered, not the missing person’s home country. If no one witnesses the person going overboard, it is almost impossible to know where and how they fell. Falling off a ship accidentally is extremely unlikely, so in most cases it's assumed to be intentional.

The captain can’t – so won’t – wait for late passengers. If you do miss 'all aboard' time you’ll need to get to the ship’s next port of call by your own means. The captain always makes several announcements if your ship itinerary includes time changes, but if you forget to adjust your watch it’s surprisingly easy to find yourself stranded. If you do get left behind, staff will leave your passport with the port authority so you can continue on alone and (hopefully) find the ship again.

The captain doesn't wait for late crew members either. While passengers might ruin their holiday by missing the ship, crew members could lose their job. If they can’t be organised enough to make it back to work on time, they will probably watch their career sail away along with the ship.

Ship spas often offer the best deals on treatments on port days, when the ship is much quieter. Crystal Cruises’ Crystal Spa and Salon manager Magarida Pinto told Frommers.com that a treatment can be priced “as much as 40% less on a day in port when there is less demand". The perfect time to get your hair done or enjoy a massage!

If you’re not that fussed about exploring the ports, visit the pool deck on a port day. On a typical sea day, most of the passengers on board flood the pool deck and fight over the limited sunbeds. Port days are much quieter, the ideal time to relax, read a book in the sun and take a dip without hundreds of kids (and adults) screaming and splashing water all over you.

The captain's quarters are generally more spacious than even the biggest guest suite on board. The living area usually includes a master bedroom and bathroom, a foyer area, kitchen and sitting room, a dining area and office. It’s not unheard of the captain to host parties or events in his quarters, but they’re strictly invite only. You might get a seat at the captain's table in the grand dining room though, if you're lucky.

OK, it's not quite as bad as a hammock on the lower deck, but crew cabins are pretty tiny. Think bunk beds, wardrobes that only fit about three outfits inside, and a bathroom so small you can shower, use the toilet and brush your teeth all at the same time. Crew are assigned to share with at least one other person and although they're usually a stranger, everyone gets to know each other pretty fast.

Like commercial airlines, ships are often on autopilot. Technically, this means there’s not always a human steering the ship. Don’t panic though, because there are always several officers on the bridge (the area where all the ship’s controls are located), even if the captain isn’t there. During stormy weather and when the ship is manoeuvring in and out of port, the captain is always at the helm. Here are 29 things only cruise ship captains know.

When the captain knows the ship is heading into a storm, he’ll alert the crew and they'll start making preparations, such as securing the gift shops and clearing the sun loungers from the decks. If you notice strategically placed sick bags popping up in communal areas of the ship, you can take it as a pretty good sign that bad weather is coming. You’ll just have to hope no one needs to use them.

Modern cruise liners cope with bad weather pretty well, but depending on the type and severity of the storm, sometimes the captain will intentionally make the ship list (lean to one side) a little against the wind. It is almost impossible for the ship to tip over completely, as its centre of gravity is very low, and the heaviest weight is contained within the lowest decks. So if you feel like you’re walking uphill, it’s probably on purpose.

When it comes to fire, being surrounded by water may give many passengers a false sense of security. Fires on ships aren't uncommon; cruise expert Professor Ross Klein testified before the U.S. Congress that there were over 60 cruise ship fires from 2009 through to 2013. It is for this reason that a team of crew members are trained specifically to fight fires on board.

In line with international safety laws, all crew members, from the entertainers to the chefs, have an emergency duty. Extensive training and twice weekly safety drills ensure that they know exactly what they have to do if the worst happens. Guests also have to participate in a safety drill on the first day of the cruise, so they know their exit routes and their lifeboat station.

Though ships have come a long way since the mistakes of the Titanic, there are not enough lifeboats on most cruise liners to carry all the guests and crew. It's actually a combination of lifeboats and life rafts that have the capacity to get everyone off the ship safely. The rafts inflate automatically in water and take up much less space, making them easier to store and deploy quickly.

Although it looks like one big glamorous, fun-filled vacation for the people who work on board, in reality cruise life is difficult. Most working days last 12-14 hours, and crew are restricted mainly to the lower decks when off duty. If you see a crew member in port it could easily be their first day on land in a month, and they're probably spending it hunting for free Wi-Fi to contact family at home. Many crew members leave all their loved ones, including their children, behind.

When the crew are working so hard, life at sea can get tedious. To relieve the boredom, crew members have been known to play jokes on unsuspecting holidaymakers. According to ElBrad on Reddit, one favourite was to mention a fictitious bowling alley to other staff in earshot of bewildered guests, who would later complain about crew-only activities on the comment cards.

Seven-day working weeks and no overtime means crew like to let their hair down at any available opportunity, and the crew bar is a prime place for such activities. Drinks are cheap, and the staff manning the bar often pour extra large measures – they are serving their mates after all. There are also regular crew parties, which often have a theme, meaning the crew get extra creative with their costumes.

Even though most cruise ships operate a crew bar, every cruise company has a set blood alcohol limit for both off and on duty crew members, to ensure crew are always able to carry out their emergency duties. If someone is breathalysed and they blow over the limit, there’s usually a zero tolerance policy. It's rare for security to do random checks, but if someone is being disruptive and is clearly well over the limit, they may as well pack their bags.

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Guests can basically drink as much as they want, and many cruise lines will let you bring your own alcohol on board, saving you some cash should you want an aperitif before dinner. There is a limit, though, and different cruise companies have different rules. And remember, if you purchase any bottles duty-free in the onboard stores, you probably won’t be allowed access to those until you leave.

Guest reviews and feedback are taken seriously by cruise companies and if it’s about a specific crew member it will be noted by their superior. “Getting all ‘excellent’ marks and a personal story on how [we] made your cruise better is the highest form of compliment to a crew member,” explained MisterPhip on Reddit. Your comments might even lead to a nomination for employee of the month, which means prize money and other perks for the crew member who wins.

From aquatic diving shows to ice skating spectaculars (yes, there are ice rinks at sea), and everything in between, most cruise ships have something for everyone to enjoy. Cruise lines spend millions on developing concepts and hiring world-class performers so that guests can experience different entertainment on every night of their holiday. Some cruise ships even house full-scale Broadway musicals, such as Cats, Chicago, and West Side Story, so if you're a theatre fan, get excited. But before you set sail, read these 27 cruise hacks you need to know before you go.

Most cruise lines offer a dedicated loyalty programme for returning guests. Staff are specifically trained to make sure they treat these repeat cruisers especially well. Your onboard room card usually indicates your passenger status, so when you flash it at boat drill or at the dining room, crew are probably taking note to see if you’re a regular. If so, expect extra-friendly service and some little perks here and there. 

There's a reason why so many people return again and again to vacation on cruise ships, despite the quirks. It's a stress-free way to see the world, with food and drink on offer 24/7, live entertainment and activities all day long. You get to see so many places that many people could only dream of. So, if you've never cruised, maybe it's time to give it a try. 

Love ships but prefer to stay on land, check out From Mayflower to Titanic: the world's most historic ships you can visit