ship passengers have been warned to make a vital switch to avoid being slapped with a "horror" bill.

- a website dedicated to credit card points and travel tips - has revealed 21 tips for first time cruise passengers to help their holiday run more smoothly, using 25 years of holiday cruising experience.

And one of the website's top tips is to keep your phone on mode as many users spoke of the "horror stories" they hear of people getting charged thousands for using their phone aboard a ship.

It said: "This can happen when you leave your phone turned on and, say, watch videos on the internet.

"Many phone plans - even international plans - do not include talking, texting and data on ships, and you'll pay exorbitant roaming rates for such services that will show up weeks later on your phone bill.

"There are ways to make calls and access the internet from ships without spending a boatload of money."

The Points Guy suggested buying a Wi-Fi package that will let you make FaceTime calls and stream videos over Wi-Fi without using phone data.

The site said: "Some phone companies have cruise-specific plans you can buy in advance of a voyage. But I personally never go that route. I keep it simple. I just put my phone in airplane mode the moment I step on board a ship and never switch it back on.

"I then turn on the phone's Wi-Fi, buy a Wi-Fi package and do all my calling, texting and internet surfing over Wi-Fi. That way, there's no way that I can be surprised by an unexpected charge."

However, it also said that cruises were in the main very enjoyable.

The site said: "For starters, you only have to unpack once, even as you travel from place to place.

"You also don't have to go hunting for a restaurant every night. There usually are a bunch just steps away from your cabin with tables waiting for you. You'll also have no trouble finding entertainment."

Other tips included booking activities in advance of boarding if possible, bringing extra toiletries due to on-board prices and not to book a cabin near the lifts.

It also suggested arriving to port a day before departure, packing your swimming costume in your carry-on, avoiding the buffet on day one and bringing your own drinks on board.