310 MARINE PRODUCTS OF COMMERCE 



of leads, and the extra cost of fan power may be offset by possible economies in 

 dunnage materials. These are factors that require careful study by designers and 

 practical engineers. It does seem clear, however, that the jacketed system can be 

 made sufficiently flexible to cope with the demands for the various cargoes with- 

 out duplication of equipment and that it will result in better control of tempera- 

 ture, humidity and carbon dioxide content with little or no increase in cost. 



It is expected of the carrier of perishable comestibles that the products be trans- 

 ported with no more change or effect on its keeping qualities than would have 

 taken place had the products not been removed from storage. That is to say, the 

 conditions that prevail in storage should prevail during the transportation episode. 

 Therefore, the problems confronting the carrier of fish are the same as those of 

 the storage operator, with the added complication that his facilities must trans- 

 port the fish as well. Transport facilities are not generally as complete and 

 desirable as the corresponding stationary storage facilities, probably because a 

 greater tolerance is permitted as a result of the mobile requirement. This fact 

 could also be due to failure to emphasize the importance of maintaining low and 

 constant temperatures, until recently not recognized as being essential. It is en- 

 couraging to find, however, that in the past decade much has been done to bring 

 the conditions in carrying means more in line with the storage conditions main- 

 tained in stationary plants. This may indicate that all the requirements will soon 

 be met both technically and economically. 



Transportation by Sea 



The application of refrigeration on ships has lagged only slightly behind that 

 on land installations. As early as 1879 frozen meat was carried from Australia to 

 Great Britain on the "Strathleven," a ship refrigerated with a cold-air machine. 

 For safety reasons cold-air machines were used rather than ammonia, but they 

 were later replaced by carbon dioxide machines because of their somewhat 

 greater flexibility. The heavy and rather inefficient carbon dioxide equipment, in 

 turn, has given way to "Freon-12," which is now generally accepted as one of the 

 least hazardous and most efficient ship refrigerants. 



Apart from limitations of space and weight and safety regulations ship insula- 

 tion can closely follow land practices. In the older ships the holds were insulated 

 with cork mostly, but in more recent installations, particularly during and since 

 World War II, the new lighter forms of insulation, such as glass-wool batts, have 

 been used with good results. Of course great care must be taken with the applica- 

 tion of any insulation on ships, particularly in the setting up of effective moisture- 

 vapor barriers in the proper places to prevent the undesirable accumulation of 

 frost and the possible breakdown of the insulation. Failiu-e of insulation in the 

 holds of vessels has almost invariably been caused by ineffective or improperly 

 applied vapor barriers. 



The methods of cooling the holds of vessels also closely follow shore-plant 

 practice. Those holds in which unfrozen perishables are carried are usually 

 refrigerated by the circulation of cooled air through a system of ducts. The air 

 is cooled in a bunker, by pipe coils or a brine spray, the density of which can be 

 controlled to give the desired humidity to the circulated air. This is sometimes 

 referred to as the "trunk" or the "bunker" system. 



Those holds in which frozen materials are carried are usually refrigerated by 



