56 
PACIFIC SCIENCE, Vol. XII, January, 1958 
resents an accepted volume of 390 times 
0.114, i.e., 44.3 m 3 . Ideally, the valve should 
accept 64.9 per cent of the volume presented 
to the mouth, i.e., of 76.7 m 3 , which is 49.8 
m 3 . On this basis the valve accepts water with 
an efficiency of 89 per cent. Since frictional 
resistance is introduced by the nets the flow 
is reduced still further. For the net of 10 
meshes per inch, the reduction is 11.5 per 
cent so that 39.2 m 3 is accepted (78.8 per cent 
efficient) ; for the 40-mesh net the volume is 
reduced by 20.4 per cent which is 35.2 m 3 
(71 per cent efficient). (See Fig. 10, upper 
curve.) 
These data demonstrate first, that the nar- 
rower aperture of the valve controls the flow 
of water into the catcher. Second, the nets 
introduce restrictions to flow, but as their 
filtering areas are adequate in relation to the 
area of the orifice controlling the flow, the 
restrictions do not change with speed, at least 
between 3 and 10 kt. Third, the catcher deals 
reasonably efficiently (89 per cent) with a 
I 
Fig. 10. Lower curve: percentage efficiencies of 
catcher with no net, and nets of 10 and 40 meshes/inch, 
relative to the calibration tube (of 9 in. diam.) when 
this is assumed to accept 100 per cent of the column of 
water presented to it. Upper curve: percentage effi- 
ciency of the catcher with no net (an absolute efficiency 
89 per cent for a valve aperture of 7 l A in.), and with 
nets of 10 and 40 meshes per inch. 
volume of water equivalent to unit length 
times the area of the valve. 
Flow Through the Catcher 
Flow through the body and tail of the 
catcher is controlled predominantly by the 
areas of their cross sections relative to that of 
the valve. The ratio between the areas of valve 
and body is 2.75, and between valve and tail, 
1.55. If the rate of flow through the valve is 
assumed to equal the towing speed, then at 
10 kt. the flow in the body is 3.65 kt. and in 
the tail, 6.5 kt. These rates assume an effi- 
ciency of 100 per cent by the valve; reduction 
of flow by the nets, and an efficiency value 
which is below 100 per cent, will lower them. 
The moderate rate in the body probably ac- 
counts for the undamaged condition of the 
plankton (see later). 
There is probably an optimum rate of flow 
through the body (and the filter) for most 
efficient working of the unit. This becomes 
a factor in any new design which proposes a 
change in the diameter of the controlling 
orifice. Thus, an increase in the diameter of the 
valve to 9 in. (which, it may be assumed, will 
equalize the volume accepted by the valve 
and that presented to the mouth) will reduce 
the ratio between the cross-sectional areas of 
body and valve to 1.78. Rate of flow through 
the body would then be 5.6 kt. for a towing 
speed of 10 kt. Such a rate may damage 
organisms beyond an acceptable amount, or 
the frictional resistance of the nets may in- 
crease to a degree where it begins to seriously 
reduce the efficiency of the catcher. It is be- 
lieved that the diameter of the valve can be 
increased, but this will probably require the 
diameter of the body to be increased also, so 
that flow does not exceed an acceptable speed, 
say of 4.5 kt. at a towing speed of 10 kt. 
Plankton Catching 
Trials of the ability of the catcher to collect 
plankton have proceeded to the extent that 
circumstances have permitted. It has not been 
possible to make repetitive hauls in one place 
