Jumping ship

With all the crazy things you can do on a cruise ship these days -- surfing, skydiving, ice skating -- it's surprising that there are still some basic things you can't do. It's clear why mass waterskiing behind a mega-ship is not a fuel-efficient proposition or how hang-gliding off the top deck could be dangerous, but it's not just the most extravagant onboard fantasies that are off limits. For a bit of fun -- and maybe even an "aha!" moment or two -- here are seven fun activities you might want to do onboard, but aren't allowed to.

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1. Hang Out in the Crew Bar

Maybe we've all been reading too many romance novels, but many single travelers find the idea of a passenger-crew member romance titillating. Combine the first flush of attraction with officers in uniform, international mystique and a bit of off-limits thrill, and you've got one fab vacation story. Cruise lines, however, do not want their hardworking crew members distracted by romantic affairs; nor do they want to face liability issues or passenger dissatisfaction when trysts go awry. For that reason, cruise ship staff are not allowed to fraternize with paying cruisers, and crew areas -- bars, dining rooms, cabins -- are off limits to passengers.

Where can you socialize with other passengers? Check out our favorite cruise ship bars.

Flying a Kite

2. Fly a Kite

The wind is strong on the upper deck of a moving cruise ship, and with the growing popularity of top-deck attractions like ropes courses and mini-golf, it's tempting to bring your own entertainment. Please don't. Cruise lines don't want you flying kites off the back of the ship, and several cruise lines indicate as much in their list of items prohibited onboard. Also, most frown on drones, balloons and anything thrown overboard. You might remember the days of skeet shooting or driving golf balls from the ship's stern; those days are long gone.

For awesome -- and legal -- top-deck fun, check out the top 10 cruise line sun decks.

3. Jump in the Water

You're sailing in the Caribbean, the water is that perfect turquoise color, and you just wish you could put on your swimsuit and dive on in. It's what you would do from a smaller boat, right? But unless your ship offers a water sports platform when it's at anchor, jumping off a cruise ship is a major no-no. That's mostly because it's very easy to die that way -- and that would put a sizeable damper on your vacation.

Ship Bridge

4. Drive the Ship

Boat-lovers are especially drawn to cruising, and we know that you all are just itching to get your hands on a cruise ship steering wheel. Sadly for you, the captain isn't giving driving lessons as part of the shore excursion program. While certain behinds-the-scenes tours include bridge visits, you won't be invited up during tricky maneuvering (like docking). You'll have to settle for a picture in the captain's chair -- and just tell your friends you took a turn at the wheel.

5. BYOB

We're going on a pleasure cruise. Pack up the cooler and ... oh, wait. While many cruise lines will kindly let you bring a bottle or two of wine onboard, most draw the line at beer and liquor. Just a few years back, more lines had lenient BYOB policies than they do now. These days, some are starting to get tough on bringing bottled water and soda onboard. On the bright side, it's one less thing to pack.

Learn more about cruise line alcohol policies.

Roller Skates

6. Roller Skate

Smooth teak decking. Oval promenades. Cruise ships just scream out for roller skating parties on deck. But unless you're in a designated rink on a Royal Caribbean ship, you are not allowed to don roller skates, rollerblades or even shoes with wheels (like Heelys) onboard. It's disappointing for sure, but you really don't want to go out of control and end up skates-over-head in the pool or -- worse -- overboard.

You can find other fun ways to work out with our favorite cruises for fitness.

7. Go Fishing

Don't you wish you could just drop a (really long) line off your balcony, sit back with your daiquiri and catch your dinner? Fishing could be more fun than team trivia and belly flop contests, but it's not allowed. Forgetting all the technical difficulties with lines and hooks and the ship's thrusters, where would you put the fish you caught? Most cruise lines won't even let you bring back the day's catch from fishing excursions on shore.