Reefer Ship - Types of Reefers

Types of Reefers

Reefer ships may be categorised into three types:

1. Side-door vessels have water tight ports on the ships hull, which open into a cargo hold. Elevators or ramps leading from the quay serve as loading and discharging access for the forklifts or conveyors. Inside these access ports or side doors, pallet lifts or another series of conveyors bring the cargo to the respective decks. This special design makes the vessels particularly well suited for inclement weather operations as the tops of the cargo holds are always closed against rain and sun.
2. Conventional vessels have a traditional cargo operation with top opening hatches and cranes/derricks. On such ships, when facing wet weather, the hatches need to be closed to prevent heavy rain from flooding the holds. Both above ship types are well suited for the handling of palletized and loose cargo.
3. Refrigerated container ships are specifically designed to carry containerised unit loads where each container has its individual refrigerated unit. These containers are nearly always twenty-foot equivalent units (often called TEU) that are the "standard" container cargo size that are loaded and unloaded at container terminals and aboard container ships. These ships differ from conventional container ships in their design and power generation and electrical distribution equipment. They need provisions made for powering each container's cooling system. Because of their ease of loading and unloading cargo many container ships are now being built or redesigned to carry refrigerated containers.

A major use of refrigerated cargo hold type ships was for the transportation of bananas and frozen meat but most of these ships have been partly replaced by refrigerated containers that have a refrigeration systems attached to the rear end of the container. While on a ship these containers are plugged into an electrical outlet (typically 440 VAC) that ties into the ship's power generation. Since many merchant vessels now have diesel-electric propulsion units installed providing power to individual units is mostly a wiring job. Refrigerated container ships are not limited by the number of refrigeration containers they can carry unlike other container ships which may be limited in their number of refrigeration outlets or have insufficient generator capacity. Each reefer container unit is typically designed with a stand-alone electrical circuit and has its own breaker switch that allows it to be connected and disconnected as required. In principal each individual unit could be repaired while the ship was still underway.

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. 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 as on the deck. Modern refrigerated container vessels are designed to incorporate a water-cooling system for containers stowed under deck. This 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 deck 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.

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. Cargoes of shrimp, asparagus, caviar and blood are considered among the most expensive refrigerated items. Bananas, fruit and meat have historically been the main cargo of refrigerated ships.