APPENDIX 19
A REPORT ON EXTENDED TESTS OF A MACHINE FOR CLASSICAL ELECTRIC FISHING

(with emphasis on eel)

by

Dr. W. Dembinśki
Instytut Rybactwa Sródladowego
Olsztyn-Kortowo, Poland

and

Dr. A. Chmielewski
Politechnika Poznanśka
Poznań, Poland

1. TECHNICAL CHARACTERISTICS

The machine consists of the petrol engine driven a.c. generator, type PAB2-1/230, 2 kVA, 230 V, and of the rectifying unit. It is capable of fishing in waters up to 1.5 m deep with conductivities ranging from 50 to 800 S/cm. This range covers almost all inland waters in Poland, excluding, however, some littoral ones which are very conductive and some extremely pure in mountains.

The rectifying unit provides also some additional safety measures against electric shock.

Rectification is performed by means of full wave bridge rectifier (semiconductor diodes) fitted with capacitive filter.

Additional safety measures are implemented by:

1. adapting the unit to be connected to the platform with a safety switch, which switches on only when the electrofisherman stands on it;

2. outfitting the unit with a special circuit for automatic switch-over from working (220–280 V) to extra-low voltage (12 V) in the event of an electrode being above the water surface and from extra-low (12 V) to working voltage (220–280 V) when both electrodes are immersed into water.

Another good point of the above automatic circuit is that it constitutes a reliable and very accurate protection of the rectifying unit, and also the generator, against overload and the effects of short-circuits. Therefore, it protects the machine from damage and from being too quickly worn away. Electric fuses, type Bi and BA are, owing to this, unnecessary. In fact they could not have given an equivalent protection. They are quite good in case of short-circuits, but one cannot rely on them in case of overload. Their characteristics are too much dispersed. Besides, it is well-known that when a fuse blows too often, then the operation team is tempted to by-pass it or replace it with a bigger one.

2. ESTIMATION OF THE MACHINE'S PERFORMANCE

Tests under practical conditions have been carried out since spring 1968 till summer 1970. The machine (Fig. 1) worked for 679 hours. This is ample for a firm assessment of the machine's performance. Let us point out that the amortisation time was taken to be 1 000 hours.

The tests took place on the State Fish Farms “Lysinin” and “Gardno” (Table I), with 81.3 percent of fishing time and 79 percent of fish caught on the lake Gardno itself.

Table I

List of lakes on which the fishing tests were carried out

The fishing technique is illustrated on Figure 2. There were three people in the fishing team. One handled the active electrode (anode), another the dip net, and third the boat. All these people were ordinary fishermen.

The results are presented in Table II, separately for spring, summer and autumn.

Table II

Results of fishing tests with the petrol engine driven s.c. generator, type PAB2-1/230, fitted with the rectifying unit for the period of spring 1968 to spring 1970

Operation costs were calculated as follows:

Generally speaking, the results given in Table II indicate that the earning capacity of the machine was very high.

2.1 Fishing Performance

Fishing performance is understood here as the result of fishing in kg per hour.

According to Table II, the mean fishing performance was 30.6 kg/h in spring, 14.7 kg/h in summer and 29.5 kg/h in autumn. Therefore in spring and autumn it was almost the same, whereas in summer about one half.

2.2 Value of Fish Caught in one Hour

This value appeared to be the biggest for spring. It was 1 159 zl (Table II). For autumn it was about half, i.e. 597 al, for summer even less than that, i.e. 457 zl.

While the fishing performance in summer when compared with autumn was half, the value of fish caught in one hour was in summer only 24 percent less than in autumn. It resulted from different species compositions for those two seasons.

2.3 Species Composition

High value of fish caught per one hour fishing time during spring is produced partly by a good fishing performance and partly by the fact that eel constituted a considerable part of the whole catch. It can be seen from Table III that in spring catches, eel constituted 53.8 percent in respect of weight and 82.0 percent in respect of value.

Very near to this was the situation in summer. Hence a relatively high value of fish caught in one hour with the fishing performance being rather low (Table II).

There was only a small number of eels in autumn. It was in respect of weight - 7.5 percent, in respect of value - 21.0 percent. This fact produced a low value of fish caught in one hour fishing time, with the fishing performance being high, almost as high as in spring.

As far as eel is concerned the best fishing performance appeared in spring - 16.5 kg/h, smaller in summer - 8.9 kg/h, the worst in autumn - 2.2 kg/h.

Pike was most numerous in autumn, i.e. 43 percent in respect of weight and 39.6 percent in respect of value (Table III).

There was a relatively small percentage of second class fish. In spring and summer it was about 12 percent, whereas in autumn 19.6 percent.

The percentages of other fish species are given in Table III.

2.4 Earning Capability

The machine turned out to be most profitable when used during spring. In this season the net profit was 743.7 zl/h (Table II). In autumn it was 349.5 zl/h, in summer - 251.7 zl/h. Mean value of this profit for the total time of tests was 512.4 zl/h.

2.5 Reliability

It is essential for such a machine to be reliable. In fact the one in question stood the test in this respect. It failed only once during 679 hours of work. The repairs cost 700 zl for the rectifying unit and 100 zl for the petrol engine driven a.c. generator.

The operational costs were therefore even lower than those estimated for calculation of the net profit.

Table III

Percentages of various fish species in fishing tests

3. REMARKS ON SOME PRACTICAL OPERATION TECHNIQUES

The special circuit to ensure automatic switch-over from high voltage working to extra-low voltage, requires that the cathode length be adjusted in such a way that the current does not exceed 10 A. The bigger the water conductivity the shorter should be the cathode. The cathode is made of bare electric wire immersed into water.

The experience gained up to the present enables us to say that:

1. with water conductivities of 500–700 S/cm the cathode should be about 0.4 – 1.0 m long;

2. with water conductivities of 300 – 500 S/cm the cathode should be 1.0 – 2.0 m long;

3. with water conductivities of about 100 – 200 S/cm the cathode should be 2.0 – 3.0 m long.

Sometimes it happens that the cathode must be shortened even to 10 cm.

Having too long a cathode, e.g. 3 m in water of 700 S/cm, would result in the machine being over-loaded. The automatic circuit does not switch on the working voltage or switch it off, if it has already been on. The machine is not allowed to work. By this fact the operation team is informed that, because of the overload, the cathode should be shortened. On the other hand one must remember that with too short cathode in pure water, the generator is not fully loaded. This fact reduces its fishing power. Therefore, with too long cathode in highly conductive water the machine could not work and with too short cathode in pure water it would be less effective. For each water conductivity there is a proper cathode length which ensures that the fishing abilities of the machine are fully used.

In view of this it is desirable to know what the water conductivity actually is. If it is not known, one should start to fish with a short cathode and then lengthen it - if fishing results are poor - up to the length with which the machine is fully loaded. One can lengthen the cathode simply by tying some more wire to it.

FIGURES 1–2

Fig. 1 Machine for classical electric fishing consisting of a petrol engine driven a.c. generator, rectifying unit safety platform and electrodes.

Fig. 2 Electrical fishing - operation technique.