BULKING
SHELFING
BOXING
BULKING, SHELFING OR BOXING?
Correct stowage
The pound should be thoroughly cleaned before stowage begins.
The bottom boards should be covered with a layer of ice 150 mm or more in depth, depending upon how well the fishroom floor is insulated, and upon the time of year and the likely length of trip.
There should be an air space of about 100 mm between the bottom boards and the floor proper.
If the bottom boards are of metal, or the fishroom floor is uninsulated, and particularly if the floor is a bare steel tanktop, then the thickness of the bottom ice layer should be increased accordingly; if no ice remains between fish and boards when the ship is discharged, then not enough ice has been used. The fish will have warmed up and will probably be spoiled.
The first layer of fish should be placed on or slid on to the bed of ice, and additional ice sprinkled over the fish to fill up the gaps between them; ideally every fish should be completely surrounded by ice.
Plenty of ice should be placed against the fishroom lining, particularly if the ship's side is uninsulated.
Further layers of fish should then be added and each layer covered with a sprinkling of ice, until the bulk stowage is within about 50 mm of the top of the shelf. For distant water voyages, about one tonne of ice should be used for every two tonnes of fish; the proportion of ice should be even higher in summer in uninsulated ships.
A layer of ice 50 to 70 mm thick should then be sprinkled over the top of the fish and ice, and the boards for the next shelf laid down.
Stowage should not be carried so high that the boards for the shelf above are supported by the bulked fish rather than by the rest angles or battens.
The second shelf is prepared by putting down a bed of ice 50 to 70 mm thick, and then adding successive layers of fish sprinkled with ice, topped with another layer of ice immediately beneath the next shelf.
Successive shelves are added until the pound is full; the top of the topmost shelf should be covered by a layer of ice about 150 mm thick to protect the fish exposed near the deckhead, whether refrigerated coils are fitted or not.
For best results the depth of each shelf of bulked fish should be not more than 500 mm.
Shelf boards should preferably be of a type that prevents dirty melt water from running down on to the fish in the shelf below, but directs it towards the walls of the pound; metal boards that overlap and have corrugations running across the width of the pound are suitable.
The fish should not be so tightly packed that melt water cannot run down between and over them.
There should still be some ice throughout the fish when the ship is discharged.
Incorrect stowage
Insufficient or incorrectly distributed ice may not cool the fish quickly enough, or may fail to keep them cool until they are landed; fish that are warmer than ice temperature will spoil much more quickly than those that are properly chilled.
A dirty pound can contaminate the mixture of fish and ice; this can make the fish unsightly, and may increase the rate of spoilage, particularly if the fish comes into direct contact with the dirty surfaces, for instance by ice melting.
Fish at the bottom of a pound can warm up considerably if they are not shielded by adequate ice; heat from the sea can be conducted through metal bottom tanks, slushwells and metal pound boards to melt the ice. Once the ice has gone, the fish themselves warm up; it should be remembered that the sea temperature, even in Arctic waters, is usually higher than that of the fishroom. Fish in direct contact with wooden or metal surfaces can rapidly develop bilgy odours of the kind associated with what are sometimes called 'stinker' fish.
If the fish in the shelf are bulked together with too little ice between them, they will cool much more slowly, and may quickly become sour. Much of the cooling effect of the ice depends upon ice-cold melt-water running down between the fish; the slightly warmer water should then meet more ice to produce more cold water. If there are large masses of fish with little or no ice between them, the fish will remain warm, and pools of stagnant melt-water will form thus encouraging spoilage.
If insufficient ice is placed against the lining of the fishroom, heat from outside can again affect the outer layers offish, particularly if the fishroom is not insulated; insulation between lining and ship's side is good insurance against incorrect distribution of the ice.
If a shelf is filled so full that the boards of the shelf above continue to rest upon the contents of the shelf even after the cargo has settled down, the fish will be unnecessarily crushed and damaged; if this happens with every shelf in a pound, the fish at the bottom of the pound may be bearing the weight of the contents of the whole pound, thus defeating the purpose of the shelves. The fish can lose weight considerably under these conditions in exactly the same way as with too deep a shelf.
If individual shelves are made too deep, the fish when landed will have lost weight; fish stowed in a shelf one meter deep can lose on average about 7% in weight between the times of stowage in, and landing from, a distant water trawler. Haddock at the bottom of a deep shelf have been known to lose as much as 15% in weight.
If the top of the pound is not covered with a thick layer of ice, the uppermost fish may be warmed up by the heat coming into the fishroom through the deck; if there are cooling grids fitted, the topmost fish can become partially frozen and dried out.
Suitability of the method
Bulk stowage, properly carried out, is a satisfactory method of preserving fish in ice.
The method requires about 2 cubic metres of fishroom space for a tonne of fish, which is much better than the stowage rate for shelfed fish, and usually somewhat better than for boxed fish.
Bulked fish may become marked and bleached by prolonged contact with pieces of ice, particularly if the ice contains large lumps; from this point of view the use of small ice flakes that have smooth, flat surfaces is to be preferred.
On occasions bulked fish of different ages become mixed during discharge, and this may make it difficult to lay out fish on the market in order of catching.
Bulked fish are subject to a considerable amount of rough handling during discharge, through the use of hooks and by transfer from pound to basket to kit.
Shelfing, more accurately described as single shelfing, is a refinement of the bulking method, whereby the fish are carefully laid out in a single layer on a bed of ice on each shelf; ideally the fish should be covered over with ice, but the term 'shelfing' in commercial practice, at least on distant water trawlers, refers to this method of laying out fish on ice, but with little or no ice on top of them. The drawbacks of this procedure are described under 'incorrect stowage'.
Correct stowage
The pound should be thoroughly cleaned before shelfing begins.
If the shelf battens are spaced at the usual 230 mm intervals it is advisable to fill the bottom shelf with ice only, especially if the fishroom floor is of metal and uninsulated.
A 50 mm layer of ice should be spread over the boards of the next shelf, and a single layer of fish placed belly down and head to tail on the bed of ice. The fish should occupy almost the whole width of the shelf, and be laid with their length along the width of the shelf, that is fore and aft in the ship.
The single layer offish should then be completely covered with a layer of ice 50 to 70 mm thick.
Correct Shelf Stowage
The next layer of boards is then laid on battens or rest angles and the shelfing process repeated. When the pound is full, the topmost layer of fish should be covered with a heavy layer of ice to protect it from heat coming in through the deck. The fish on each shelf should be protected by extra ice against the fishroom lining, particularly if the ship's side is uninsulated.
Melt water should drain away to the ends of the shelf boards, and not drip down on to the fish and ice on the shelf below.
Incorrect stowage
If the fish are shelfed in the bottom shelf of a pound, there is unlikely to be room for sufficient ice beneath the fish; the fishroom floor can conduct enough heat to melt away the bed of ice before the fish are landed, leaving them unprotected and open to more rapid spoilage.
Incorrect Shelf Stowage
If the fish are laid out other than with the bellies downwards, puddles of stagnant water and blood can lie in the belly cavities and hasten spoilage.
Single-shelfed fish laid out on ice, but without ice on top or with a mere sprinkling of ice along the noses, are cooled from one side only; they therefore cool down less rapidly than fish that have ice all round them, and the backs and heads of fish shelfed in this way can remain quite warm throughout stowage. Spoilage originating from the gills can then spread rapidly along the backbone. Shelfed fish of this kind have been found to be decidedly inferior in quality after twelve days in ice compared with bulked fish of the same age; on occasions there have been marked differences in quality between them after only three days.
Inadequate protection by ice of the fish at the top and at the back of the pound can result in the outermost fish becoming too warm and spoiling rapidly.
Occasionally during heavy fishing, some of the catch is double-shelfed or bulk-shelfed; the first layer of fish is put down on ice as for single shelfing, and then a second layer of fish is laid belly up on top of the first. Sometimes a third layer of fish may be added, this time belly down, and so on with further layers; then the top of the mass of fish is iced. This method has nothing to recommend it since it combines the worst features of bulking and of shelfing; the large mass of warm fish is neither properly iced nor properly drained, and is very susceptible to rapid spoilage.
Suitability of the method
Single shelfing with ice on top of the fish, is a satisfactory method of stowage for chilled fish; but shelfing as practised on board distant water trawlers can encourage excessive spoilage of the catch.
Shelfed fish require more labour and much more space for stowage than bulked fish; the stowage rate is about 4-5 cubic metres per tonne.
Once the heavy catching rate of the immediate post-war period had declined a little, crews had time to take more care with the stowage of the catch; it was found that better prices could be obtained for fish from the last part of the catch if they were laid out individually, particularly when they were not covered with ice, since they then retained much of their moist, attractive bloom. Merchants began to associate good quality with the term 'shelfed' fish, since they were noticeably better in appearance and were always caught during the last part of the voyage. As a result, the term shelfed fish became synonymous with quality regardless of when the fish were caught or how they were stowed; one merchant was for a long time under the impression that the term referred to fish caught on the Continental Shelf!
It cannot be emphasised too strongly that the practice of shelfing fish without ice on top of them introduces an unnecessary element of risk of greater spoilage; in spite of the good appearance of the fish, certainly after twelve days in ice, and often very much sooner, the eating quality can be inferior to that of bulked or boxed fish. It is very much safer to ice over each shelf; because of the extra care taken in laying out, and avoidance of any great pressure on the fish, the quality can then be at least equal to, and often better than, bulked fish of the same age, no matter at what point in the voyage shelfing begins. It is often claimed that shelfed fish suffer less damage from crushing than bulk fish, and lose less weight; neither of these advantages would be lost by covering each layer of fish with ice.
Correct stowage
Properly carried out, and using suitable boxes, this method of stowage can produce better quality fish at landing than either of the other two methods, and can help to ensure that the fish deteriorate as little as possible after landing.
The box must be properly designed for the job. It must have sufficient room in it for the amount of fish required plus enough ice to protect the fish until they are landed. It should not be so deep that fish at the bottom of the box are squashed, and must be long enough to accommodate without bending most of the larger fish that are caught. At the same time it must not be so unwieldy that it cannot be handled comfortably by one or two men as required either at sea or at the port. The boxes should stack to a reasonable height when full without distortion or collapse of the bottom box, in order to reduce the number of supporting shelves in the fishroom or to do away with the need for shelves altogether; this will help to keep down the amount of wasted space in the fishroom and so increase the stowage rate. The boxes should also preferably nest when empty, so that there is sufficient room for stowage at the start of fishing.
The box should have drain holes so arranged that melt water does not drain on to the fish below. It is difficult to design a nesting box that does this; the type shown drains into the box below. Drain holes can be placed to restrict drainage to the ends of the box, or alternatively, a box can be designed to have good draining properties but without the nesting facility. It should be of a material that is easily cleaned and kept clean, and that does not taint the contents and is suitable for contact with food. It should be robust enough to withstand working conditions on a trawler, and be suitable for use with mechanised equipment for rapid discharge and handling at the quayside, since one of the important advantages of boxing at sea is that the fish can be discharged and transported ashore in the same box without further rehandling from one container to another. The box should have provision for marking on it the nature, quantity and date of capture of the contents. The boxes used at any one port, and preferably over a much wider area, should be of uniform design and size, so that central facilities can be provided for cleaning, maintaining and distributing the boxes.
The boxes must be clean before stowage begins.
Ice should be placed in the bottom of the box to a depth of 50 to 70 mm.
The box should then be filled with fish laid belly down and mixed with ice, and the contents covered with a further layer of ice 50 to 70 mm deep.
The box must not be filled so full that the contents, whether or not they are protected by a lid, can be squashed when another box is placed on top.
The boxes should be stacked on battens to keep them clear of the fishroom floor; the air spaces between the floor battens can be filled with ice if there is little or no insulation on the floor. Similarly, if bulkheads and ship's sides are not well insulated, the tiers of boxes should be supported clear of bulkheads and linings, and the spaces between support battens filled with ice.
The contents and the date should be recorded on each box at the time of stowage, and the boxes so disposed that they can be discharged approximately in order of age of contents.
Incorrect stowage
If the box is not big enough for fish and ice, then the fish will almost certainly be stowed in insufficient ice; fish at the bottom of a box with no ice beneath them or fish at the top of the box with no ice above them, will have the bottom of one box, and possibly the lid of another, between them and the nearest layer of ice. Fish under these conditions will cool slowly, if at all, and may spoil very rapidly indeed; fish in direct contact with the surface of the box can also develop sour, bilgy odours very soon after stowage, producing what are sometimes called 'stinkers'.
Boxes with awkward corners and ledges, or with fittings such as rope handles, are extremely difficult to clean, and can harbour dirt and bacteria, as can boxes made of porous, easily punctured materials; such boxes can defeat attempts to keep the fish in a wholesome condition.
Fish in boxes that have been overfilled will become squashed, lose weight, and appear unattractive.
If boxes are stowed too close to tanktop or fishroom lining without adequate protection by ice or insulation, the contents can become warm and spoil quickly.
Suitability of the method
Boxing of fish at sea can be the most satisfactory method of stowing fish in ice, particularly when the fish can be landed in the same boxes and distributed without further rehandling.
A standard box of correct design is essential for the satisfactory working of any boxing scheme; such a box could simplify the whole process of stowage and landing.
The age, size and species of fish in boxes are easily recorded; accurate identification of the catch is possible when laying out on the market.
The stowage rate for boxed fish is reasonably good, somewhere in the region of 2-7 cubic metres per tonne, which is considerably better than that for shelfed fish, and approaching that for bulked fish; with some improvement in design of box, stowage rate may well equal or surpass bulk stowage rate.
The use of a standard box throughout a port could alleviate quayside congestion, and make possible the provision of central facilities for cleaning and distribution of boxes.
Boxed fish are not likely to be crushed or bruised to the same extent as when bulked fish are incorrectly stowed, and are therefore less likely to lose weight.
Boxing requires that the merchants buy by sample; weight and quality of contents of all boxes bearing the same date of capture must be taken on trust after inspection of representative lots, if full advantage is to be taken of the method. Disturbance of the contents of every box offered for sale would defeat the purpose of using the same box at sea as for shore distribution.
Boxing is consistently safer than the present method of shelfing; if shelfed fish were stowed with ice on top, then quality would be equal to, or better than, the bulked fish. Boxing has the greatest future potential, since it fits better into schemes for handling fish by modern methods; used properly, boxing can produce better quality fish and help to maintain that quality from time of catching until the fish reach the merchants and processors.
If shelfing in its present form is to continue, then it must be confined to the last part of a voyage.
Most distant water trawlers land catches partly bulked and partly shelfed; there would be less likelihood of mixing of the catch during discharge if bulked stowage were confined to those parts of the fishroom pounds below staging level, and shelfed fish kept above the stage. arrangement of the fishroom with bulked pounds aft and shelf pounds forward often causes unnecessary mixing; adjacent pounds containing different ages of fish are often worked out together during discharge and the contents of one allowed to slide into another. If all the fish above the stage were known to have been caught later in the trip than those below stage, the discharge could be carried out in two clearly distinct steps and the new and the old kept apart.
There is little to recommend stowage of any one voyage by two different methods; shallow bulking of the whole trip would be preferable to incorrect shelfing of the last part of the catch combined with occasional changes back to bulking when fishing becomes too heavy for the crew to cope with the catch as individual fish; bulk-shelfing is an even more unsatisfactory solution.
Boxing should not be combined with other methods of stowage on the same voyage; many of the benefits of boxed stowage are lost if the fish-room has to be fitted to accommodate bulked or shelfed fish, and shore handling arrangements for mixed stowage can become complex.
To sum up, only one method of stowage should be used. Shallow bulking is perfectly satisfactory, shelfing in its present form is not; boxing can be the best way of stowing fish, and should be seriously considered for the future.
If you have any queries, write, phone or call at either of the addresses given below:
|
The Director |
The Officer in Charge |
|
Torry Research Station |
Humber Laboratory |
|
PO Box 31 |
Wassand Street |
|
135 Abbey Road |
Hull |
|
Aberdeen |
HU3 4AR |
|
AB9 8DG |
|
|
Tel: 0224 877071 |
Tel: 0482 27879 |
61 Gaping of fillets, by R. M. LOVE.
62 The freezing time of fish, by F. J. NICHOLSON.
63 Fishing ports in the UK, by J. J. WATERMAN.
64 Fish silage, by I. TATTERSON and M. L. WINDSOR.
65 Fishworking machinery, by S. MAIR.
66 Handling and processing mackerel, by J. N. KEAY.
67 The haddock, by J. J. WATERMAN.
68 Icemaking plant, by J. GRAHAM
69 Cook-freeze fish products, by J. N. KEAY.
70 Advice for the fish industry; who does what, by J. J.
WATERMAN.
71 Processing cod; the influence of season and fishing ground,
by R. M. LOVE.
72 Reducing odour in fish meal production.
73 Stowage of fish in chilled sea water, by J.H.
KELMAN.
74 Handling and processing rainbow trout, by A.
MILLS.
75 Freezing small pelagic fish, by I. MCDONALD.
76 Dark colour in white fish flesh, by R. M. LOVE.
77 Squid, by G. D. STROUD.
78 Health hazards of handling industrial fish, by A.
WARD.
79 Minced fish by J. N. KEAY.
Earlier notes in the series, most of which are still available, are summarized in:
60 Key to Advisory Notes 1-59, by J. J. WATERMAN.
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