Seawater or Freshwater
When ice production is considered in fishing boats, seawater will be the natural raw material selection. When deciding whether to use freshwater or seawater in land-based plants, the decision will depend on several factors, such as the availability of regular materials, the location of the ice facility, and the intended use of ice (eg for use in fishing) ships or on the shore. It should be remembered that whichever water is used, the resulting ice will come into direct contact with food. For this reason, it is essential that the water used is free of contamination that may cause unacceptable human health or fish staining. This means that the water must be of drinking water quality and must comply with safety standards set by bodies such as the World Health Organization.
The use of seawater ice for fish cooling has been studied for several years, and with the development of suitable small ice machines that can be installed in fishing boats, this alternative becomes more suitable for fishermen.
The main advantages of seawater ice use:
• It can be produced at sea or on coasts where freshwater shortages are a serious problem or freshwater is expensive.
• Since the space on fishing vessels is limited, the ability to produce ice when needed and needed can have practical advantages, rather than anticipating needs before fishing begins.
• Slightly lower storage temperatures can be achieved with seawater ice; therefore, the shelf life of the fish can be extended. Commercially available flake/scale ice machines can produce seawater ice with temperature and variable salt content from -9 ° C to -20 ° C.
However, there are some major disadvantages, for example:
• Seawater ice is not homogeneous and when stored, it may be a mixture of ice crystals and chilled salt solution, which are semi-fluid inconsistencies and filter the saline solution as the ice rises at temperature. Therefore, seawater ice does not have a fixed melting point (-1.5 ° C to -2 ° C for seawater ice with a salt content of 3 to 3.6 percent) and losses due to the melting and leaching of the brine solution to the storage temperature. will depend.
• Due to its variable temperature, there is a risk of partial salting of fish and salt absorption (especially in thin-skinned fish) when using seawater ice.
• To obtain the highest quality ice, machines specially designed for seawater ice production are needed. These are more expensive to purchase and operate than ice machines designed for freshwater ice production.
Ice production capacities may vary depending on the evaporator and water temperatures, refrigerant type, and ice thickness. Therefore, the above data is the average seawater ice output leaving the ice maker at a temperature of -20 ° C under the conditions listed above.
The following design factors should be considered for onboard seawater ice machines:
• The facility should be able to produce and produce ice under extreme slope and rolling conditions of fishing boats.
• The facility should be made of non-corrosive materials (such as high-quality stainless steel, aluminum, plastic, rubber, and fiberglass) to resist the marine environment.
• Equipment needs to operate at a lower temperature than freshwater ice machines - usually between -18 and -21 ° C because of seawater freezes at a lower temperature than freshwater.
The advantages of having built-in ice machines especially for fishermen dedicated to fresh fish production can be summarized as follows:
• It provides flexibility in catch volume and opening length.
• After the initial purchase costs of the machine, ice production can be less costly and only includes proper maintenance and repair of the ice machine.
• The fisherman is not dependent on the coastal facilities for the ice resources to go fishing; ice can be produced as and when required.
• Being able to produce ice onboard can overcome problems that arise when a boat loaded with ice on the shore has little or no fishing. Ice costs can constitute a significant percentage of operational costs in many countries.
The main disadvantages are:
• Machinery and auxiliary power, conveyors, etc. Purchase and installation costs of any auxiliary equipment that may be required.
• The ice produced is usually made from saltwater, which can affect some fish species through salt absorption into the product.
• If care is not taken to use only clean seawater, there may be ice and consequently contamination.
• Machine maintenance will require some special technical expertise.
• Additional power is required.
• Qualified labor and maintenance services are required (possibly onboard).
The most common type of ice machine to be placed on a small fishing vessel would be a flake ice machine. Table 2.1 gives some features of the leaf ice makers that can produce seawater ice suitable for use in small and medium-size fishing boats.
Table 2.2 gives some typical sizes for various “pack” ice machines suitable for installation on fishing boats, according to the manufacturers. All machines shown are water-cooled models, except for the Coldisc model. Some examples are given to other machines to show how changes in dimensions affect their production capacity.
However, it is not necessary to put ice makers into the sea to use ice at sea. As mentioned earlier, ice can be moved from one place to another and is a portable form of cooling. This ensures that ice made in coastal plants is taken into the sea and used when necessary.