Self-contained units are typically the best choice for smaller boats, up to about 40 feet (12m), due to the lower cost of the units and installation.
A self-contained air conditioner has all of the major components mounted on a single chassis, which is installed in the living area; usually under a bunk or settee, or in a locker. Cooling-only models are available, as well as reverse-cycle, which can cool or heat. Also available are air conditioning kits, which include the self-contained unit, water pump, ducting, and grilles -- all the components needed for a complete system.