A reefer ship is a type of ship typically used to transport perishable commodities which require temperature-controlled transportation, mostly fruits, meat, fish, vegetables, dairy products and other foodstuffs.
Reeferships may be split into three categories:
A major use of refrigerated cargo hold type ships was for the transportation of bananas but has since been partly replaced by refrigerated containers that have a refrigeration system attached to the rear end of the container. While on a ship this is plugged into an electrical outlet (typically 440 VAC) that ties into the ship's power generation. Refrigerated container ships are not limited by the amount of
containers they can carry unlike other container ships which lack sufficient refrigeration outlets or have insufficient generator capacity. Each reefer container unit is designed with a stand-alone electrical circuit and has its own breaker switch that allows it to be connected and disconnected as required.
Refrigerated cargo is a key part of the income for some shipping companies. On multi-purpose ships, Refrigerated containers are mostly carried above deck as they have to be checked for proper operation. Also, a major part of the refrigeration system (such as a compressor) may fail, which would have to be replaced or unplugged quickly in the event of a fire. This being the case, no provisions for refrigerated cargo power connections are made below the hatch covers that enclose the top of the hatches aboard a ship. Modern container vessels stow the reefer containers in cell guides with adjacent inspection walkways that enable reefer containers to be carried in the holds as well.
Modern refrigerated container vessels are designed to incorporate a water-cooling system for containers stowed under deck. This is does not replace the refrigeration system but facilitates cooling down of the external machinery. Containers stowed on the exposed upper deck are air-cooled while those under-decks are water cooled systems. The water cooling design allows capacity loads of refrigerated containers under deck as it enables the dissipation of the high amount of heat they generate. This system draws fresh water from the ship's water supply which in turn transfers the heat through heat exchangers to the abundantly available sea water.