>I don't quite understand how cruise ships can be that bad.
Many many reasons. Cruise ships use some of the worst, most polluting fuel in general. They are barely a step above floating coal power plants. They also have significantly fewer systems to "filter" the exhaust compared to a power plant. Despite that, they have insane energy needs.
Medium cruise ships are capable of over 50 Megawatts of power generation. They usually have about 10 megawatts of constant "hotel" load. These ships are air conditioning a huge volume, extremely leaky in terms of insulation, and are constantly in the hot and humid tropics. They also have to "generate", ie boil and condense, tens of gallons of water per person, per day. 10 Megawatts for about 3500 people is not great. A megawatt can conservatively power 500 homes. They also rarely use power hookups in port, so they will be running that 10 megawatts of diesel output even in port.
Cruise ships also do not steam for efficiency the way most merchant vessels do, but rather to meet a strict timetable like an airline. The same medium cruise ship will spend about 30 megawatts to go 25 knots from port to port.
Many of those things also seem to apply to large hotel and leisure resorts -- huge volume, leaky construction, hot environment. I wonder how much power they allocate per guest.
The points regarding energy intensive water treatment and less efficient movement are well taken, though.
Many many reasons. Cruise ships use some of the worst, most polluting fuel in general. They are barely a step above floating coal power plants. They also have significantly fewer systems to "filter" the exhaust compared to a power plant. Despite that, they have insane energy needs.
Medium cruise ships are capable of over 50 Megawatts of power generation. They usually have about 10 megawatts of constant "hotel" load. These ships are air conditioning a huge volume, extremely leaky in terms of insulation, and are constantly in the hot and humid tropics. They also have to "generate", ie boil and condense, tens of gallons of water per person, per day. 10 Megawatts for about 3500 people is not great. A megawatt can conservatively power 500 homes. They also rarely use power hookups in port, so they will be running that 10 megawatts of diesel output even in port.
Cruise ships also do not steam for efficiency the way most merchant vessels do, but rather to meet a strict timetable like an airline. The same medium cruise ship will spend about 30 megawatts to go 25 knots from port to port.