A. L I N I N G O F T H E H O L D AND P E N B O A R D S
F i g u r e 6 shows the typical construction of a fish hold in a large trawler.
T h e fish rooms in smaller vessels do not, in principle, differ m u c h from this. T h e floor of the hold, in w h i c h drain channels a r e cut running fore and aft, is concrete. T h e channels empty the melting ( b i l g e ) w a t e r into the well.
1. Wood
T h e most c o m m o n l y used material for the side lining, intermediate wing bulkheads, and loose pen boards is w o o d c o a t e d with shellac, var
nish, or special types of white fish-room enamels or lacquers. Quality of
material, workmanship, and painting, and subsequent cleaning and maintenance are governing factors in the successful use of wood, b e c a u s e this material requires constant vigilance in order to prevent its b e c o m i n g damaged, water-soaked, and consequently contaminated with slime and bacteria.
WELL
FIG. 6. The inside of a large trawler fish room. The concrete floor has two channels that deposit the water from the melting ice into a well connected with a pump. Galvanized steel pen-board stanchions (studs) make possible the division of the fish room into pens. Such a pen is shown, where the pen boards are made of wood (Fisheries Technological Laboratory, Copenhagen).
M a c C a l l u m ( 1 9 5 5 a ) stowed iced fish in the laboratory and on board a ship against various materials used for lining. H e examined worn wooden boards, freshly planed and painted or varnished boards, and transparent plastic and aluminum alloy sheets. H e found that strong bilgy odors developed quickly in the fish against the worn boards, while almost all fish in contact with the other materials ( a l u m i n u m sheet b e i n g the b e s t ) , w e r e free from bilgy and sour odors. No benefit was derived from brushing and washing the worn boards in w a r m water. M a c C a l l u m draws attention to the well-known fact that it is very difficult to keep wooden boards well painted or varnished and he therefore suggests that metal lining b e m o r e widely used.
2. Metal
O n the other hand, it is true that aluminum or other light metal alloys h a v e many advantages and in recent years these have b e e n installed in
a n u m b e r of boats ( F i e d l e r , 1 9 5 3 ; Anonymous, 1 9 5 3 a ) . S o m e boats have a wooden lining with wing bulkheads and boards of metal.
T h e primary disadvantage of such a lining is its high cost. Aluminum lining is said to corrode quickly and is not as resistant to rough handling (e.g., shovels and i c e p i c k s ) as wood. However, at the time of writing, several boats fitted 7 - 9 years ago with sea-water-resistant aluminum alloy have not shown m u c h d a m a g e nor are they corroded. T h e hygienic prop
erties of aluminum are also an advantage and t h e cost of cleaning a metal hold is less than that of a wooden room. T h e r e m a y finally b e some saving resulting from the difference in weight b e t w e e n wooden lining plus wooden boards as c o m p a r e d with a similar outfit of light metal.
A c o m m o n m e t h o d of fish hold construction using metal lining takes the form of prefabricated panels sandwiching a layer of insulation and secured to wooden grounds on t h e ship's frames. T h e joints b e t w e e n panels are either covered with simple strips, w h i c h some consider in
sufficient to obtain a watertight seam, or they are argon-welded or m a d e b y special fittings (Anonymous, 1 9 5 5 b ) .
M a c C a l l u m claims that in a well-insulated, metal-lined room con
siderably less i c e is required for stowing than in an insulated wooden hold, w h e r e it is necessary to b a n k a heavy layer of ice against the p e n sides to prevent contact with t h e wood and t h e consequent danger of bilgy fish. M o r e light needs to b e thrown on this question, as well as on the relative importance of h e a t conduction from the air of the fish room to the fish b y the metal partitions and boards, which of course are excellent h e a t conductors.
3. Plastic
A n e w lining material m a d e from glass fiber and polyester resin has b e e n fitted in refrigerated fruit cargo-liners ( M a u , 1 9 5 6 ) . I t is claimed that the material is resistant to salt w a t e r and fish juices and presents another possible solution to t h e lining problems in fish holds.
B . I N S U L A T I O N
In subtropical and tropical waters, insulation of t h e sides of the fish room is considered indispensable. I n temperate climates, however, apart from wooden lining and air space b e t w e e n it and the sides of the ship, m a n y ships are without insulation except at the bulkhead dividing t h e fish hold from the engine room. O n e of the reasons is that ice is c h e a p and that insulation is an added expense that also makes repair work more complicated.
Insulation, on the other hand, is b e c o m i n g m o r e and more common.
Besides affording a considerable saving in ice, stowing of the fish is less
laborious on long distance trips. I f fish are to b e k e p t sufficiently chilled in an uninsulated vessel, it is necessary during stowing to build 1 ft. of ice up against the walls o f the fish hold. I n a well-insulated boat, the normal amount of i c e properly deployed is sufficient to preserve even t h e fish near the ship's side ( R e a y , 1 9 5 1 ) .
In wooden boats, insulation is rarely used in t e m p e r a t e waters. O n e reason is the good insulating properties of the wood itself; another, that rot in the wood m a y easily occur in places w h e r e outside air cannot k e e p the wood dry. Special precautions, therefore, must b e taken ( M e s c h k a t , 1 9 5 1 ) .
T h e following tabulation indicates h e a t transfer in a hold during summer months calculated in tons of i c e on a 6-day trip for an unin
sulated E a s t Canadian trawler and for the same ship provided with 4 inches of insulation ( D u n n , 1 9 4 6 ) .
Uninsulated Insulated
Heat through deck 6.1 1.3
Heat through bulkhead 3.2 0.8
Heat through hull 4.3 1.7
Cooling 100 tons of fish 11.1 11.1
Heat through open hatches, etc., 1.3 1.3 Cooling of hold inside when ice is
loaded 0.9 0.9
26.0 17.1
T h e calculation was b a s e d on the insulation material b e i n g dry. T h i s often is not the case, and information about relative w a t e r resistance and loss of insulating p o w e r b y moisture absorption is therefore important when selecting insulation material and determining the m a n n e r in which it is to b e fitted a n d p r o t e c t e d from fish-hold juices, sea water, a n d t h e moisture that condenses in the space b e t w e e n the outer hull and the inside lining. Gutters or drain pipes are often installed at t h e b o t t o m of this space.
T h e insulation material most c o m m o n l y used is expanded cork a n d cork plate, in m a n y cases c e m e n t e d to the hull of the ship. Thicknesses of 4 inches for t e m p e r a t e and 8 inches for w a r m waters are preferred.
E x p a n d e d plastic materials are lately preferred in British and Canadian ships, frequently in 2-inch layers. T h e y are w a t e r resistant a n d light.
Aluminum foil, glass-wool, and rockwool have also b e e n used in r e c e n t trawler constructions ( R a t h k e , 1 9 5 1 ; Busse, 1 9 5 5 ) . W h e n mineral wools are used in wood-lined holds, an impervious layer fitted b e t w e e n t h e wood and the insulation should b e applied, or the absorbtion of moisture should b e controlled b y such dehumidification systems as are in use in refrigerated cargo liners ( N i e m a n n , 1 9 5 4 ; M a u , 1 9 5 6 ) .
T h e floors of the fish room m a y b e a difficult problem. T e m p e r a t u r e measurements of the steel of the tank top in a room with uninsulated floors was found to b e within 1 or 2 centigrade degrees of sea tempera
ture ( W a t e r m a n , 1 9 6 0 ) . I t is strongly recommended, therefore, that all fish-room floors b e either properly insulated and then waterproofed and sheathed to prevent d a m a g e from boards and ice axes, etc., or at least that the metal b e covered with portable wooden boarding.
C. M E C H A N I C A L R E F R I G E R A T I O N
Installation of m e c h a n i c a l refrigeration in fish holds is increasing.
T h e total n u m b e r of refrigerated boats is, however, relatively insigni
ficant.
1. Coils Enveloping the Hold
In some boats fishing in tropical waters, the fish room is enveloped in a system of refrigerating coils ( C o s t a , 1 9 5 6 ) . I n old boats, t h e coils are fastened on t h e inside of t h e walls, which, a m o n g other inconven
iences, leads to local freezing of the fish. I n n e w boats, t h e coils are b e hind the lining and under the floor, with openings to increase the cooling efficiency.
2. Coils or Grids under Deck Only
M o s t vessels with refrigeration are fitted with grids or coils under the deck only. T h e main function of these is to cool the empty fish rooms, shelves, and stanchions, to prevent the ice from melting during the out
ward journey, and to preserve the i c e in a crisp and easily workable condition. T h e saving in ice is normally estimated at around 2 0 - 2 5 % in summertime. Coils or grids placed under the deck c a n also k e e p t h e air cool a b o v e shelved fish and prevent excessive melting of i c e on top of pens in boats with insufficient insulation under t h e deck. M e c h a n i c a l refrigeration of this kind cannot influence t h e temperature of any fish that is m o r e than a few inches down in t h e stowage.
M e c h a n i c a l refrigeration on b o a r d has some drawbacks, t h e main ones being t h e following: E x p o s e d surfaces of fish (e.g., "shelved" fish) will tend to get dry and lose bloom. T h e temperature of t h e air in t h e hold is not uniform and the placing of thermometers and thermostats is therefore difficult. W r o n g l y placed, they might cause some of the fish to freeze. F u r t h e r m o r e , the air temperature must b e high enough to bring about a reasonable melting of ice from the beginning of fishing to unload
ing at port. I f not, the fish m a y have a shorter storage life than in a well iced, unrefrigerated hold ( s e e Section V , A ) . S o m e skippers consequently prefer not to use refrigeration on the h o m e w a r d journey.
3. Jacketed Fish Holds
T h e idea of enveloping t h e fish hold completely with a cold j a c k e t has also b e e n suggested and tried out experimentally (Ofterdinger, 1 9 5 0 ; M a c C a l l u m , 1 9 5 5 b ) . I n C a n a d a , w h e r e most such work has b e e n carried out, several boats h a v e b e e n fitted this way. Holds are insulated with cork or expanded plastic inside the jacket, the inner lining consisting o f aluminum. C o l d air is blown through the jacket, t h e p o w e r for t h e com
pressor b e i n g supplied b y a diesel generator. I n order to r e d u c e t h e cost of installing a metal-lined, j a c k e t e d hold, "unit pens" h a v e b e e n designed.
Comparisons of quality of landings from these C a n a d i a n boats with those from normal wood-lined, unrefrigerated boats showed that fish from the latter w e r e definitely inferior. M o r e research is n e e d e d in this general area.
A detailed estimate of cost of construction and m a i n t e n a n c e of a wooden fish hold c o m p a r e d with a "unit p e n " m e t a l hold has b e e n m a d e
( M a c C a l l u m , 1 9 5 5 a ) .