Transport of reefer containers
More and more refrigerated cargoes are carried in containers. On the other hand, high cube boxes are more and more popular. To be operationally efficient, new container carriers should be able to transport a large number of reefer boxes both on open deck as well as in holds optimized for high units. This creates new technical problems with respect to hull construction, ventilation, electrical power supply and control systems. Instead of a number of electrical plugs fitted on board, a suitable class notation shall be used to define reefer capacity of the vessel.
In order to accommodate reefer containers, the ship shall be provided with sufficient electrical power and a hold ventilation system able to deliver 4500 m3/h to each 40ft reefer box. A separate air duct shall serve each container stack. Air ducts shall have adjustable openings or elastic hoses to direct air to the lower part (1/3 height) of the container independent of the stowage pattern. Generally, each duct shall be served by its own fan, except for hold sides where two outermost air ducts can be served by one common fan. However the number of reefer 40ft containers served by one fan shall not exceed 16.
It is not easy to supply such a huge quantity of air, however much more difficult it is to enable a proper airflow through the hold to air outlet. Two solutions can be adopted:
1. Exhaust vents should be located between transverse hatch coamings on vessels with minimum freeboard.
2. Longitudinal gaps between hatch covers are natural air outlets on vessels with high freeboard, and in addition vents in longitudinal sides of hatch covers could be arranged.
Other problem is the requirement of Load Line Convention to close all openings in severe weather conditions. With longitudinal hatch coamings without openings, the outlet boxes located between transverse coamings are well protected against green water and most of them submerge at very large heel angle only. On the contrary, vent openings in longitudinal sides of hatch covers are not protected and in sever weather conditions at least 50% of them must be closed.
The best arrangement of air outlet is to combine both solutions in order to have at least 60%-70% of air outlets working even if venting openings at one side of hatch covers are closed.
Under sea-going conditions, the number and rating of service generators shall be sufficient to supply all sockets and the hold ventilation in addition to the ship essential services when any generator set is out of service. Ships designed for the carriage of more than 150 reefer containers are to be equipped with a remote reefer container monitoring system of the power cable transmission type.
Suitable accesses are to be provided to containers on deck and in holds for the maintenance and replacement of compressors and fans.