Posted on Leave a comment

Refrigerated Cargoes

Preparations to be carried out prior to Loading Refrigerated Cargoes:

  • Reefer cargo should be loaded onboard only under the supervision of a recognized surveyor.
  • Cargo should not be allowed to wait for long time on the quay.
  • Hold should be pre-cooled to temp below the carriage temp.
  • Damp, wet and torn packages should be inspected if the cargo has deteriorated. If the cargo is fine then only it should be loaded after re-packing.
  • Contents of at least 5-10% cartons should be examined from each hold on a random basis.
  • Cartons with soft or dripping contents should bedocume rejected.
  • Refrigeration of holds should be turned on during long breaks and during meal breaks.
  • Once loaded, the cargo should be covered with tarpaulin.
  • During operations, the frost formed on top of the bripe pipes should be brushed carefully. It should not fall on top of the cargo.
  • In tropical climates avoid loading in the noon. Try to load cargo during night time.
  • Upon completion of loading, the reefer chamber must be closed air tight and cooling resumed immediately.

Principle & Working of different types of Refrigerated Cargo:-

1. Closed Reefer: This is a conventional type refrigerated container. It comes in one-piece with integral front wall and an all-electric automatic cooling and heating unit for ISO sea-going containers.

2. Modified/ Controlled Atmosphere (MA/CA) reefer containers: These type of insulated shipping containers maintain a constant atmosphere by replacing consumed oxygen using an air exchange system, keeping an ideal atmosphere in equilibrium with the product’s deterioration rate.

3. Automatic Fresh Air Management Containers: Popularly known by its acronym – AFAM reefer containers uses advanced technology to regulate the air combination by automatically adjusting the scale of fresh air exchange. It works similar to Controlled Atmosphere refrigerated container, controlling the composition of oxygen, carbon dioxide and others. The controls of the AFAM refrigerated containers can be adjusted to influence and extend the shelf lives of the cargo they carry.


Maintenance / Preparation of Cargo holds on board a Reefer vessel:

  • Depending upon the degree of littering, different methods of cleaning are to be used; For normal carton-packed cargoes with or without dunnage, it is usually enough to sweep the compartments. After meat and fish cargoes washing is almost always necessary.  Sweeping must be carefully done and all dirt removed from the compartments. The holds should be swept as they are emptied and the dirt should be removed when the cargo has been discharged. If any cartons are broken and dunnage is spread all over the compartments, the situation is more complicated.

It has to be checked that goods from the cartons are not hidden anywhere on deck beams, in remote inaccessible corners or under the gratings. In these cases it is necessary to remove every piece of grating and sweep under it. Spot washes should be done, where cargo has come loose, been damaged or treaded down into gratings.

If the holds are badly littered, a careful washing has to be performed with a high pressure machine with a suitable washing detergent for the first cleaning, where after rinsing must be done carefully. If necessary, it must be deodorised using ozone, sodium bicarbonate or patent deodorisers but strong disinfectants not be used. The high pressure jet should not be applied at right angles to clean the surface but diagonally to the surface so that the jets cut away the dirt from the surface. The prescriptions from the supplier regarding the dosis of detergent must be carefully followed.

When cleaning it must be carefully checked that the whole compartments will be cleaned on the bulkheads as well as on and under decks with special care to deck beams and girders under deck on the upper side. The gratings should be cleaned properly including the bottom side as required.

The cooler rooms which contain the blowers and coils need to be also cleaned as and when required. The trays under the coolers must be kept clean. The purpose of these trays is to collect condensed water and melted ice and if necessary leakage from the coolers.

  • Scuppers are to be cleaned and brine traps checked, tested and refilled. Brine traps prevent warm air from entering the compartment and cold air from escaping; at the time same time allowing drainage of water.

Bilges and scupper drains should be clean and clear. Bilge pumping arrangements should be in working order and capable of pumping each bilge dry.

  • During cleaning it should be checked that the air flow channels are cleaned and when carrying out repairs to them special attention should be paid that the channels are not blocked.

Return air grids should be intact and clear. The air openings between the trays and the coolers are necessary in order to let the air pass. If this space is cluttered up, the air circulation will be throttled. Air ducts should be unobstructed. Fresh air flaps or valves should be free to move. The circulation and fresh air fans should be working satisfactorily.

  • The covers of the cargo hold lights should be intact. The hatch cover hydraulic system should be free of leakages. The cargo holds should be free of loose rust and paint chips.
  • The insulation and permanent dunnage is to be checked and repaired as required.
  • The hatch covers should be weathertight. All the gratings should be intact. Gratings should be free of moving and/ or tilting and/or sliding. The grating decks should have an even surface (flush). All spar deck beams should be intact and the spar decks should have an even surface (flush).
  • Pallet suitability:- The pallet side-boards should be intact. Instructions would be received for the use of pallet side-boards. Pallet problem areas should be identified and attended to. All pallet instructions should be removed, marked or made flush.
  • Signs:- Hygiene signs should be placed onboard before commencement of loading. The signs `NO SMOKING’ and `USE WALKING BOARDS’ should be painted in the hatch coamings.
  • Reefer Machinery:- Refrigeration system should be clear of leakages. The refrigeration machinery should be in working condition and adequate for the intended voyage and the electrical generating capacity should be sufficient for the intended voyage.
  • Reefer Monitoring Equipment:- Delivery and return air sensors should be calibrated by an ice bucket test regularly. USDA air and pulp sensors also should be calibrated by an ice bucket test. CO2 sensors should be operating properly. The humidity sensing and recording equipment should be working properly. Thermometers should be in position and ventilator plugs to the compartment fitted in place and tightly wedged.
  • All openings are to be sealed against entry of air.
  • Brine pipes are to be tested to ensure that they are not choked and that no leaks occur at the joints
  • Stores Stocks:- Sufficient cargo handling materials like Walking Boards, Slings, T Bars and Air bags should be available.
  • 360 Quality certificate:- The vessel should have a valid 360 Quality certificate. 


Indirect Method & Second Refrigerant (Brine Cooling) :

  • The primary refrigerant is used to cool a tank of brine and this cooled brine is then circulated through the compartment.
  • Brine is chosen because of its low freezing point, 20° to 30°C, depending on its concentration and composition.    
  • The brine is passed through separate grids surrounding the same compartment.
  • If one grid is blocked or chocked, the brine supply can be increased to other grids so that cooling will not be affected.
  • Cooling is carried out by a combination of cold brine and cool air circulation.
Refrigeration System (Brine Cooling) on Reefer Ships

Handling Reefer Cargo:

Frozen Cargo: Meat, Butter, Poultry and Fish. -8OC To -12OC

Chilled Cargo: Cheese, Eggs and Fresh Vegetables. -2OC To 6OC

Air Cooled Cargo: Fruits. 2OC to 12OC

Preparation of cargo hold:

  • The compartment must be clean, dry and free of any odour or taint,
  • Hold must be deodorised with mild agents (lime, ozone),
  • Bilges to be cleaned, dry, deodorised and suctions checked,
  • The insulation and permanent dunnage to be checked and repaired as necessary,
  • Scuppers to be cleaned,
  • Brine traps to be checked, tested and refilled,
  • Thermometers to be in position,
  • Ventilator plugs in position and tightly wedged,
  • Brine pipes to be tested to ensure they are not chocked and that no leaks occur at the joints.

Precooling of the compartment:

  • The compartment should be cooled down prior to loading to a temperature slightly lower than the transit temperature, Dunnage laid in the compartment should also be cooled down otherwise it will stain the cargo.

Precautions during loading:

  • Reefer cargo should be loaded onboard only under the supervision of a recognized surveyor,
  • Cargo should not be allowed to wait for long time on the quay,
  • Hold should be pre-cooled to temp below the carriage temp,
  • Damp, wet and torn packages should be inspected if the cargo has deteriorated. If the cargo is fine then only it should be loaded after re-packing,
  • Contents of at least 5-10% cartons should be examined from each hold on a random basis,
  • Cartons with soft or dripping contents should be rejected,
  • Refrigeration of holds should be turned on during long breaks and during meal breaks,
  • Once loaded, the cargo should be covered with tarpaulin,
  • During operations, the frost formed on top of the bripe pipes should be brushed carefully. It should not fall on top of the cargo.
  • In tropical climates avoid loading in the noon. Try to load cargo during night time,
  • Upon completion of loading, the reefer chamber must be closed air tight and cooling resumed immediately.

Precautions during Stowage:-

  • Cargo must be stowed in order to allow free circulation of air through and around the stow.
  • Laying of dunnage should be such that it does not obstruct designed air flow pattern in the compartment,
  • Sides and bulkheads should be fitted with vertical dunnage to keep cargo away from the structure,
  • Reefer chambers must be divided with air channels for each block not exceeding 3 mtrs. Channel must be atleast 10cms wide and aligned to face the cool air outlets. There should be an even gap of atleast 30 cms between the cargo top and the lowest part of the deckhead.
  • Dunnaging should be efficiently carried out so as to avoid stow collapsing into the air channels.

Each lot of cargo to be loaded according to the b/ls and separated by using colour tapes or net. Avoid loading cargo for more than 1 port in one chamber. Cargo once loaded should not be shifted. These measures will help prevent temperature fluctuations.


Refrigerated cargo is divided into 3 categories:

  1. Frozen cargoes
  2. Chilled cargoes
  3. Cooled cargoes

Frozen Cargoes

  • e.g. Meat, butter, poultry and fish.
  • These cargoes are carried in a hard frozen state at temperatures around-8°C to -18°C to prevent the growth of bacteria.

Chilled Cargoes

  • e.g. cheese, eggs, fruits and fresh vegetables.
  • Beef may also be carried in a chilled state as the tissues get damaged sometimes by freezing.
  • Temperatures maintained around 6°C to -2°C.
  • It is more critical to maintain right temperatures of chilled cargoes as condensation of moisture due to variation of temperature encourages bacterial growth.

Cooled Cargoes

  • e.g. fruits and fresh vegetables.
  • Temperatures maintained around 2°C to 13°C by air circulation.
  • The temperature at which the above cargoes are carried may vary beyond the above mentioned limits depending on
  • the nature of the cargo,
  • the ambient temperature at the load port,
  • the duration of the voyage
  • and the state in which the cargo is to be delivered (whether ripe, frozen, ready for consumption, etc.

PRINCIPLE OF REFRIGERATION:-

  • Just as the natural flow of water is from a high level to a low level,
  • the natural flow of heat too is from a body at high temperature to a body at a low temperature,
  • and just as we would need a pump to reverse the flow or pump water upwards,
  • we need mechanical work to be done or a heat pump to transfer heat from a body at a low temperature and give it to a body at a high temperature.
Principle & Working of a Refrigeration System
  • In a refrigeration system,
  • gas at a high pr. P¹, low vol. V¹ & high temp T¹ (35°C to 40°C) is obtained from the compressor.
  • It is allowed to expand slightly & cool in the condenser to a liquid at pressure P², vol. V² & SW temp T².
  • This cooled liquid gas is suddenly allowed to expand by passing through an expansion valve.
  • The expansion of the gas to vol. V³ is accompanied by a slight fall in its pressure P³ and a large fall in its temp. to T³(5°C to 25°C).
  • The gas is now kept in contact with the substance to be cooled.
  • It absorbs heat from the substance and cools it, while in turn its own temp rises to T⁴ (25° to 35°C) and pressure & volume to P⁴ & V⁴ respectively.
  • It is then compressed in a compressor to its pressure, volume & temperature at the first stage, i.e. P¹, V¹ & T¹.

REFRIGERATION SYSTEMS:- There are two types of refrigeration systems:

1. Direct systems:

  • In small refrigerated chambers on small ships and provision stores on ships.
  • In large installations it is difficult to monitor the pipes for leakages, wastage of expensive gas would results. Due to which a indirect system is used on large ships/compartments.   

2. Indirect method and a second refrigerant:

  • The primary refrigerant is used to cool a tank of brine and this cooled brine is then circulated through the compartment.
  • Brine is chosen because of its low freezing point, 20° to 30°C, depending on its concentration and composition.    
  • The brine is passed through separate grids surrounding the same compartment.
  • If one grid is blocked or chocked, the brine supply can be increased to other grids so that cooling will not be affected.
  • Cooling is carried out by a combination of cold brine and cool air circulation.
Refrigerated Cargoes - Brine Grids

Precautions to be taken during the Voyage to protect cargoes which are liable to freeze:

  • Solidification in the cargo tanks can occur when solidifying cargoes are stowed adjacent to “cold cargoes” or cold ballast water in adjacent spaces.
  • Tank bottoms must therefore always be checked for hard factions especially when carrying vegetable and animal oils, at regular intervals throughout the voyage and always prior to arrival in the discharge port.
  • To avoid solidification of cargo in adjacent tanks, do not ballast the ballast tanks in contact with the surrounding the cargo tanks. Keep the ballast water in these ballast tanks about 30 cm below the tank top, allowing for trim.
  • Special care must be exercised when the vessel is advised that the shore tanks have been “squeezed” (swept) into the vessel, in such cases the “squeezed” (swept) cargo from the shore tank should as far as possible be confined to one tank onboard. The particular tank onboard which received this cargo can then be re-circulated onboard if soundings indicate a “hard bottom” problem. Solidification can also occur when inhibited cargoes or their condensates are exposed to excessive heat. If excessive heat is caused by the sun, spraying the deck area with seawater may prevent this type of solidification (polymerisation).
  • Because of the risk of solidifying cargo being hard and blocking the venting pipe due to evaporation through the vent pipe, the following precautions are recommended:
    • During voyage, regular checking of proper functioning of PV valves.
    • During voyage, regular checking of the vent lines by N2 / air depending on the type of cargo.
    • During tank cleaning, PV valves, vent lines to be thoroughly washed with hot water and same to be drained to the tank.
    • After the loading, all cargo lines to be flushed with high pressure N2 / air depending on the type of cargo.

General Outline of Refrigeration Systems Onboard Reefer ships:

Refrigeration process system requirements: Refrigeration is a process in which the temperature of a space or its contents is reduced to below that of their surroundings. Refrigeration is used in the carriage of some liquefied gases and bulk chemicals , in air conditioning systems, to cool bulk CO2 for fire fighting systems and to preserve perishable foodstuffs during transport of foodstuff .

Ships refrigerate cooling on plant may vary from the small domestic refrigerating unit for provisions to large plant for reefer vessels. The Chief Engineer is responsible for the correct temperatures being maintained, delegating the good operations and maintenance of the plant to the 2/E. Larger plants may have a Refrigeration Officer. Machinery under ship’s engineer responsibility may include:

  • Domestic ref. plant.
  • Cargo ref. plants
  • Air conditioning plants
  • Ventilation and heating plants
  • Cargo refrigerated containers

All maintenance recommendations from the makers have to be carried out regularly and according to instructions, entered in the refrigeration maintenance log, together with the test of all cut outs, i.e. HP, LP, LO, HT, that have to be carried out at regular intervals, generally one month.

All adjustment must be made according to standard good practice and records of the same entered in the log.

Filter separators and driers should be regularly cleaned in order to have always the circuit moisture, dirty and oil free. When shutting down a plant all refrigerant gas must be pumped in the liquid receiver or condenser.

Refrigeration of cargo spaces and storerooms employs a system of components to remove heat from the space being cooled. This heat is transferred to another body at a lower temperature. The cooling of air for air conditioning entails a similar process.

The transfer of heat takes place in a simple system: firstly, in the evaporator where the lower temperature of the refrigerant cools the body of the space being cooled; and secondly, in the condenser where the refrigerant is cooled by air or water. The usual system employed for marine refrigeration plants is the vapour compression cycle as shown in diagram here.

Refrigeration Systems onboard Reefer ships - Vapour Compression Cycle
Fig: Vapour compression cycle

The pressure of the refrigerant gas is increased in the compressor and it thereby becomes hot. This hot, high-pressure gas is passed through into a condenser. Depending on the particular application, the refrigerant gas will be cooled either by air or water, and because it is still at a high pressure it will condense. The liquid refrigerant is then distributed through a pipe network until it reaches a control valve alongside an evaporator where the cooling is required. This regulating valve meters the flow of liquid refrigerant into the evaporator, which is at a lower pressure. Air from the cooled space or air conditioning system is passed over the evaporator and boils off the liquid refrigerant, at the same time cooling the air.

The design of the system and evaporator should be such that all the liquid refrigerant is boiled off and the gas slightly superheated before it returns to the compressor at a low pressure to be recompressed.

Thus it will be seen that heat that is transferred from the air to the evaporator is then pumped round the system until it reaches the condenser where it is transferred or rejected to the ambient air or water.

It should be noted that where an air-cooled condenser is employed in very small plants, such as provision storerooms, adequate ventilation is required to help remove the heat being rejected by the condenser. Also, in the case of water-cooled condensers, fresh water or sea water may be employed. Fresh water is usual when a central fresh-water/sea-water heat exchanger is employed for all engine room requirements. Where this is the case, because of the higher cooling-water temperature to the condenser, delivery temperatures from condensers will be higher than that on a sea water cooling system.

Temperature Records: – Temperatures of domestic refrigerated rooms have to be corrected daily by the 2nd Engineer or delegated Officer, passed to the Chief Engineer and to the Master. On larger plant suitable logs will be supplied in order to enter temperature of the cargo and all other relevant details.

Leave a Reply