25
GPP ELECTROFISHER
www.smith-root.com
falls distinctly from 324 to 265
volts when using two anodes.
However with a very large wire
netting cathode efficiency falls
only slightly from 324 to 302
volts when using two anodes.
For shore-side operations, the
cathode surface presents the
least resistance when it is divided
into several parts placed several
meters apart. An electrode is
more effective when its form is
least concentrated. For example,
a 3'x12' strip is more effective
than a square of 6'x6'.
Figure 10 illustrates the
variation in both voltage and
gradient between the electrodes.
Whenever possible, the
cathode should be placed in
parts of the stream that you do
not wish to fish, or even in parts
completely separated from the
stream itself. The anode should
never be allowed to come close
to where the cathode is located.
35
9
9
Resistance ohms
of anode field
90
50
90
50
between anode and cathode
125
85
99
59
Potential difference volts
between cathode and water
126
185
32
54
324
265
324
302
a. one
anode
Standard 0.5m
2
grid cathode
b. two
anodes
anode
anodes
Large wire-
netting cathode
Figure 9. Comparison of two sizes of cathode.
326
450
450
356
3.6
1.62
5.9
2.38
3.6
1.28
6.0
2.15
between anode and water
c. one
d. two
total
Current amps
Power kilowatts
35
of cathode
Resistivity of the water in all cases=143 mho/cm
Figure 9. Comparison of two sizes of
cathode.
2
4
46
48
Total potential (volts)
Distance from center of anode (meters)
1.0
1.5
2.0
2.5
3.0
0.5
3.5
Anode
Cathode
Potential gradient (volts/cm
)
Potential
Gradient
00
100
200
300
Figure 10. Variation of potential and gradient.
Figure 10. Variation of potential and
gradient.
BOAT CATHODES
Many aluminum electrofishing
boats use the boat hull as
the cathode and the boom
electrodes as the anode. This
is perfectly safe as long as you
never come in contact with
the anode and complete the
electrical circuit. The National
Safety Council in their data sheet
#1-696-85 does not recommend
using the boat hull as the
cathode, but we have yet to
hear of any accidents occurring
because of it.
Figure 11 shows a Smith-Root
tote barge designed for stream
wading operations. Note the
large cathode plate attached
to the bottom of the fiberglass
hull. The anode is a pair of ring
electrodes about 28cm (11") in
diameter mounted on fiberglass
poles. With this arrangement,
the resistance of the anode
pair is four times the cathode
resistance. Thus, four times as
much voltage appears in the
anode field as in the cathode
field, and consequently 80% of
the applied voltage appears at
each electrode.
The situation could be
further improved by enlarging
the cathode, but a point of
Figure 11. Bottom mounted cathode
plate on SR-6.
diminishing returns is reached.
Doubling the cathode size would
halve the cathode resistance
and give an 8 to 1 ratio between
anode and cathode resistance.
Now 88% of the voltage would
appear at the anode. This is only
an 8% improvement, and is not
worth the additional physical
problems associated with the
larger cathode.
The SR-6 field tested with
two 28cm anodes and a voltage
of 240 volts, showed good
fishing effectiveness in 400
microSiemens/cm conductivity
with a current of 3 to 4 amperes.
In lower conductivities of 40
microSiemens/cm, a current of 1
to 1.5 amp is effective. This data
may serve as a useful bench-
mark to judge whether a unit is
operating under conditions such
that fish should be caught. If the
electrical performance is close
to this reference point, and fish
are not being caught, it is safe to
conclude there are few fish in the
area.
INTRODUCTION TO ELECTROFISHING
