Gratingless Air Circ System in Reefer Ships Proves Successful

Computer simulations and tests have been carried out by LauritzenCool and York Marine AB to confirm the suitability to distribute air in refrigerated cargo holds without gratings. The investigated grating-less concept was confirmed successful by full-scale transports of bananas in a regular service over a period of half a year from Central America to Europe. The work has given valuable information in developing formulas and algorithms to design safe systems for grating-less holds in refrigerated ships. The project started in 1994 with laboratory work at ABB Ventilation Products to find criteria for the rate of cooling of bananas on single pallets. Soon, tests moved on to trials to determine the rate of cooling and temperature gradients in several pallets of bananas and citrus. Finally, regular shipments with bananas on pallets on the MV Ivory Dawn were carried out during a period of six months in a service from Central America to Europe. The tests and shipments have given valuable information to determine the criteria for the design and optimisation of systems for grating-less holds for the next generation of refrigerated ships. Two different executions of the system were evaluated - supply of air under the pallets versus supply of air above the pallets by means of high velocity air jets tangent to a flush ceiling. Criteria for volume, speed and pressure of the air, geometrical limitations of the cargo holds and other requirements that all give an as good as in today's conventional refrigerated ships or even better cooling rates and keeping of the temperatures of all types of produce on pallets in refrigerated cargo holds have been determined. In addition, the project has given valuable information in developing the necessary formulas, algorithms and computer simulation programs in order to design a safe system for grating-less holds in refrigerated ships. The group working in the project has also looked at required technical arrangements to load and discharge ships with a grating-less system. To build ships with a grating-less system for distribution of the air in the cargo holds means savings in the investment of the ship on gratings, lower moulded depth of the hull for the same capacity and a higher stability to carry containers on deck. From an operational point of view, it means no costs for replacement of damaged gratings, less cost for cleaning and less cost in disturbances during loading and discharging.