The reefer 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 two categories:
-Sidedoor vessels have sidedoors that are lowered to the quay and serve as loading and discharging ramps for the forklifts. In the rear of the sidedoor there is a double pallet elevator, which brings the cargo to the respective decks. This special design makes the vessels particularly well suited for short distance trade.
- Conventional vessels have a traditional cargo operation with hatches and cranes/derricks well suited for the handling of palletized and loose cargo.
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 forward end of the container. While on a ship this is plugged into a 380 VAC outlet that ties into the ship's power generation. Many ships are limited by the amount of refrigeration containers they can carry due to the lack of refrigeration outlets or insufficient generator capacity. Each reefer container has its own breaker switch that allows it to be connected and disconnected in adverse weather with the power off.
Refrigerated cargo is a key part of the income for some shipping companies. Refrigerated containers are mostly carried above deck as they have to be checked for proper operation, they may have to have a major part such as a compressor fail which has to be replaced, or they may need to be unplugged quickly as in the event of a fire. As such, this means 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 cellguides with adjacent inspection walkways that enable reefer containers to be carried in the holds as well.
Some modern container vessels also incorporate a water-cooling system that enables the container's own refrigeration system to be disconnected, as they are rather inefficient below deck, due to the high amount of heat they generate. This system draws fresh water from the ship's water supply that has been cooled to a preset level.
There are also refrigeration systems that have two compressors for very precise and low temperature operation, such as transporting a container full of blood to a war zone. Containers of shrimp, caviar, and blood are among the most expensive refrigerated items.