Almost every ship has only one 110 outlet in the main cabin. So always bring, at least a ten foot, extension cord.
As a former CPAP user I always carried an extension cord, with a multi plug end, in the CPAP carrying case. The extension cord STAYED in the case and was not used for anything else.
Most hotels, motels, cruise ships and some of your friends homes do not have outlets next to the bed and the extension cord is a life saver. A CPAP should never be placed on the floor because it will suck up the carpet dust and contaminants that sink to the floor. The filter will filter most of them out but your CPAP will "smell" and I don't take the chance.
The cords are cheap and can be found at any hardware store, Wal-Mart, or other store. Buy one and keep it in the machine's carrying case.