It is generally cool at night and you can get a nice cross breeze by opening up your windows so air conditioning is rarely needed.
However, some of our larger catamarans do have air-conditioning:
Lagoon 400 (some models)
It is important to note that when the yachts are anchored in port the air conditioning works on a generator and can certainly be used, however it isn’t possible to use it all night because they are not made for heavy usage. This also requires a large amount of fuel.