18 BULLETIN 1290, U. S. DEPARTMENT OF AGRICULTURE 
The fruit temperatures in the top and bottom layers in the various 
stacks showed very slight differences (fig. 8), particularly in the 
loadings in which there was no dunnage and in which dunnage in 
every other layer was used. In both cases where dunnage was used 
in every layer, however, the temperature was lower than where either 
of the other methods of stacking was employed, though this differ- 
ence was very slight. It is to be expected, particularly with the type 
of installation on the ship, that the fruit in the top and bottom layers, 
even though different methods of stacking are used, will be but 
slightly affected, owing to the fact that the racks with which the 
compartments are fitted allow a 4-inch air space between the deck and 
the bottom of the load. There is also considerable space between the 
top of the load and the deck above, which allows for adequate air 
circulation. The cold air as it issues from the sides of the hold 
readily passes over and under the load, coming in direct contact with 
the top and bottom layers ; consequently, very little difference in tem- 
perature due to the use of dunnage can be expected at these points. 
The difficulty in cooling the middle of a load of fruit, even in 
relatively small bulk, has long been recognized. This difficulty is 
increased in the ship's hold, where the bulk of the fruit confined in 
one space is large and in these experiments at a temperature of about 
80° F. when loaded. There is no clear passage for the air to travel 
through the load, as there is under the floor racks and over the load. 
It must be expected then that the fruit in the middle layer and in 
the center of the load will not be so easily refrigerated as that in 
the top and bottom layers, owing to the difficulty of securing ade- 
quate air circulation even when the air is forced through. Only by 
the use of dunnage can air channels be provided. Of course, methods 
of stacking could be worked out that would allow for air channels, 
but such methods would cause broken stowage and cut down the car- 
rying capacity of the vessel. 
The average temperature of the middle layers in which no dun- 
nage was used (fig. 8) was reduced from 74° F. at San Juan to 
64° at the end of the trip, a total average reduction of 10 degrees. 
Where dunnage was used in every other layer the reduction was 11 
degrees, and where it was used in every layer the average lowering 
of the temperature in the boxes of fruit in the interior of the stacks 
was 14 degrees. In other words, the heat removed from the fruit 
was 40 per cent more where dunnage was used for every layer than 
where no dunnage was used and 27 per cent more than where dun- 
nage was used in every other layer. This clearly shows the value 
of air space between the boxes, which can be provided by the judic- 
ious use of dunnage. There seems to be no question that the effi- 
ciency of the refrigerating equipment in cooling down fruit and 
holding it at the lower temperature is considerably increased by the 
use of dunnage for every layer. 
The cost of dunnage for this purpose is not high, as it may con- 
sist of rough lumber 1 by 2, 1 by 3, or 1 by 4 inches and only 2 lineal 
feet are needed per box of fruit above the first layer. The dunnage 
can be used over and over again. Short lengths are very useful, 
especially in filling out at the sides of the hold and under hatchways 
whore the cargo is to be broken out. The use of plenty of dunnage 
was found to be an inexpensive way of increasing the efficiency of 
I lie ship as a fruit carrier, 
