Where self contained units are considered unsuitable, this could be for space-limited or noise-critical vessels, then the condensing unit (the compressor with the sea water cooled condenser) is "split" from the air handler and placed in an engine room or other remote space. The air-handler / evaporator remains in the space to be conditioned and the two parts are connected by insulated copper refrigerant lines.
A single larger condensing unit located in a machine space or engine room can be connected to several air handlers (also called evaporators) located in separate cabins, this creates a very quiet, efficient system but is generally more expensive due to higher equipment cost and because the system must be charged with refrigerant by a certified engineer.