Plankton Catcher — Bary ET AL. 
51 
which holds the upstream end of the net to 
the frame. At the rear the struts attach to a 
flange (3, 4, k") which fits snugly about the 
cod end of the net. The cod end, in turn, is 
forced against the flange by a conically 
shaped stretcher ring (4, h') 9 fitted internally. 
Radial fins (3,4,/ ') extend outward from the 
flange to a deep thrust ring (3, 4, /) When 
the frame and net are inserted into the body 
from the rear, the thrust ring locates the after 
end (Fig. 3), and the clamp ring locates the 
forward end (Fig. 2). The forward end of the 
tail has an internal diameter 3/16 in. less than 
the after end of the body. When the tail is 
on, an internal lip is formed (3, 4, m) which 
abuts against the rear edge of the thrust ring, 
and provides a thrust surface. The assembly 
serves to push the net from the downflow end 
into the water entering through the valve. 
On removing the tail the frame is retained by 
a spring clip which is attached to the thrust 
ring, and which engages with the body. The 
tail is locked onto the body by a simple, ex- 
ternal catch after a part turn has been made 
over locking studs (3, 4, /). The plankton 
bucket (1, 3, 4, h") is removed after releasing 
a clip and also making a part turn over locking 
studs (3, 4, j). Its rear end is streamlined 
where it extends back into the tail piece. 
The depth-flow meter (Currie and Foxton, 
1957) is fastened in the tail on two runners 
(Figs. 3, 4, j, s'). It can be slid rearwards, 
clear of the end of the tail, to facilitate its 
being handled and read. The impellors turn 
only with forward motion of the catcher and 
rotate a drum on which a smoked glass 
cylinder is slipped. We have modified the 
meter so that the drum in turn drives a dial- 
type revolution counter (3, 4, s"). A Bourdon 
pressure unit is attached to a pen and, on 
reduction of pressure, causes a longitudinal 
trace to be made on the smoked cylinder. 
During a vertical tow, this is combined with 
rotation of the cylinder, when a helical trace 
results, from which depth and flow can be 
obtained. In a horizontal tow, the revolution 
counter gives the number of turns made by 
the cylinder while the trace on its surface 
gives the depth to which the catcher was 
lowered, and at which it was towed. The 
amount of water which passes through the 
net during the period of lowering is also 
indicated. 
The weight of the catcher is 120 pounds 
(54.5 kilos) when rigged for horizontal tow- 
ing, and 130 pounds (59 kilos) for vertical 
towing. To these must be added, respectively, 
45 pounds (20 kilos) for a depressor (Fig. 7), 
and 45 pounds for a lead sinker (Fig. 5). 
TOWING ATTACHMENTS AND RELEASE ARM 
Vertical Towing 
Vertical towing requires forward and after 
brackets for attaching the wire to the catcher 
(Figs. 1, 2, 4, n, n' , and o, o'). The catcher is 
supported by the forward bracket on a stop 
(1, 2, 4, w) on the wire; the after bracket is 
a spacer. Free rotation about the wire is al- 
lowed. The wire is inserted via a slot (3, r) 
into a central rotating portion (1, 3, 4, r" 1 
which turns through 180° and is locked in 
place by a spring clip (1, 3, 4, r'). Initially 
forward and after brackets were similar. Each 
held the wire about 7 in. off the side of the 
catcher, but this method introduced many 
difficulties and had to be abandoned. In the 
method now employed the after bracket re- 
mains, but the forward bracket (a temporary 
one, see Figs. 1, 2, 4, n) offsets the wire by 
only 3 in. It is inserted in, and attached to, the 
horizontal towing bracket (1, 2, 4, p) which 
has a U-shaped section. Underwater observa- 
tions indicate that at a vertical towing speed 
of 2 to 3 kt. rhe catcher is at an angle of about 
5°, but as the speed is increased to 6 kt. the 
angle progressively decreases until for all 
practical purposes, the unit tows in a vertical 
position. 
The heavy sinker (45 pounds, Fig. 5) is not 
necessary when towing vertically, but is es- 
sential during rapid lowering to reduce a 
tendency in the catcher to dive nose first. As 
the valve is open, the catcher would be fishing 
