Refrigerated Sea Water System

All types of sea foods are perishable. Once bacteria action starts, as shown in Fig. 1, it cannot reverse; at best stopped from further deterioration, it is therefore imperative that preservation starts at the very beginning. It is said that “Fish of Pakistan is one of the Best in the World as long as it is in water”, the moment it is on deck deterioration starts from the way it is handled and then preserved. During the 1970’s FAO had passed a verdict that Pakistani wooden fishing trawlers can never be made hygienic. In the 70 years of history, fishermen being conservative in nature, local efforts have achieved half-baked lining and insulation of holds, albeit still using the same methods of stacking and manual handling. The result is encouraging as now to some degree B grade is achieved in some percentage of catch. Grade A quantities are small and still out of reach in most cases.

The process of getting cold water into the fish hold starts from suction from sea, passing this water through the heat exchanger of a refrigerated system where in expanded cool gas is passed on one side and sea water on the other. This water is pumped into the fish holds from the top and sprayed evenly over the entire area.

Once the water had reached the desired level, it is recirculated through bottom suction to obtain the desired temperature. Depending on the quantity of catch, the water level and temperature are maintained for optimum results. Generally, this translates to thirty percent water and seventy percent catch. It is noteworthy that the normal capacity of fish holds is around 45 tons of catch

RSW tanks are normally constructed adjacent to one another spanning the width (beam) of the vessel. There are usually 2, 3, 6, etc. storage tanks on board a single vessel. The storage tanks are normally loaded to a capacity of approximately 80% fish and 20% water, depending on the type of fish. The tanks must be properly insulated from the hull, deck heads, machinery- and accommodation spaces to limit the possibility of heat ingress as much as possible. Furthermore the tanks must be equipped with over-flow and equalizing pipes. It is essential that the interior surfaces of the tanks have a smooth finish, with no obstructions or sharp edges.

• High cost of ice blocks.
• Unhygienic water used in making of ice pollutes the fishes.
• Sharp corners of crushed ice pierces the skin of fishes causing bacterial degeneration and loss of proteins.
• Low quality of fishes due to delayed handling.
• Low cooling efficiency for catches as compared to RSW System.
• Stacked fishes stresses the lowest layer.
• Carrying full load of ice increases fuel consumption.
• Ice may or may not be utilized which leads to waste of ice and money.