freecia

Most cruise lines geared towards Americans and Australians prohibit guests from bringing their own kettle or coffee pot. They also don't allow clothing irons, surge protectors, and clothing steamers. Such items are confiscated if found and returned at the end of the cruise. Cruises departing from the UK usually have kettles in the rooms or available. Norwegian and Tui/Mein Schiff (a German cruise agency partially owned by Royal Caribbean) offer coffee makers in balcony cabins and higher. Car ferries seem to be ok with kettles.

I usually bring a thermos and a silicon mug/cup cover like this on cruises I fill them with hot water from the buffet. The cup cover allows me to take a filled mug back to my cabin and also keeps my drink warmer. Just push the lid down the burp out air and it'll be much safer to take down a rocking hallway than a cup with a hole in the lid. You can usually also get hot water via room service, dining room, or at a pay coffee bar. I'm picky about hot water taste and temperature (I can't stand coffee flavored hot water) so it is usually a jaunt to the buffet or pay coffee bar for me.

The smallest hot water maker combination is an immersion coil and a cup.