lection of a regular supply of samples frozen 

 in a series with accurately defined circumstan- 

 ces. In this way a detailed picture can be ob- 

 tained of the effects of all phases of brine 

 freezing annually. This will also help to over- 

 come the problem of the considerable amount 

 of time it takes the staff to obtain samples at 

 sea. A preliminary study of quicker chilling 

 and freezing on a large scale was made aboard 

 a commercial tuna vessel, the MV Westport 

 with the cooperation of its owner, National 

 Marine Terminal Inc. of San Diego, whose staff 

 and crews gave outstanding help. Two heat 

 exchangers were installed on the Westport with 

 a series of brine spreaders in two wells (Fig. 

 2). This system will enable brine to be cooled 

 more rapidly than at present. A shakedown 

 investigation revealed that this system has 

 some merit. 



One serious source of loss, damage, and poor 

 refrigeration is the overpacking of wells. This 

 not only puts pressure on the fish at the bottom 



but increases the ratio of fish to brine from a 

 designed figure of around 3.5: 1 to nearer 5.5: 1. 

 The passage of the brine is obstructed through 

 many parts of the load, thus reducing the rate 

 at which it can transfer heat from the fish to 

 the coils. The eflfects are particularly pro- 

 nounced with skipjack, which has a fragile skin 

 and is smaller and softer, and so packs down 

 more readily. The obvious answer to this is to 

 fill less tuna into the wells. However, the eco- 

 nomics of operation discourage the fisherman 

 from doing this. Even if his loss of acceptable 

 tuna is increased by overpacking, it is still not, 

 as a rule, equal to the extra amount he packs in, 

 so that the net turnout of his vessel is larger and 

 his income greater. Thus he has no economic 

 incentive to pack correctly. If a reduction in 

 packing were to give substantially better qual- 

 ity and if as a result he were to receive a pre- 

 mium rate for his quality fish, he could afford to 

 pack his wells lighter. At present, it is not clear 

 whether the packer could recover the necessary 



(A) PRESENT SYSTEM 



i 



COMPRE SSOR 



CONDENSOR 



RECEIVER 



BRINE 

 WELL 



EX PAN SI ON 

 VALVE 



I 



_J 



BRINE CIRCULATING PUMP 



(B) PRESENT SYSTEM WITH 

 HEAT EXCHANGER 



BRINE 



f 



COMPRESSOR 



CONDEN SOR 



. AMMONIA 



HEAT 

 EXCHANGER 



BRINE CIRCULATING PUMP 



Figure 2. — Schematic diagram of brine immersian freezing system used for freezing tuna aboard com- 

 mercial fishing vessels. 



