Modern electronic devices used for fishing.pptx

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1. Modern electronic devices used for fishing By veeramani

2. Fishing equipment Traditional fishermen had their own innovative methods, based on their observations and experience, which even now continue to play an important role in fish finding . Now a time we are used more sophisticated fishing vessels and methods, increasing the range of fishing operations. Acoustic methods introduced for depth measurement and detection of submarines have been successfully adopted for fish finding . The use of electro-acoustic equipments like echo sounder, sonar and net sonde has become almost indispensable in industrial fishing not only to find fish , but also to collect information such as depth, nature of bed, position of net, fish behaviour , etc .

3. Echo sounder The most widely used fish-detection instruments is the echo sounder T hough it was primarily developed for depth measurement, its efficiency has been improved with time to record even the very weak echo signals reflected by the fish. Both echo sounders and fish finders are essentially the same but for additional features in a fish finder like more powerful amplifiers to receive and amplify the weak fish echoes.

4. Components of an echo sounder There are Four main components, 1. Transmitter 2. T ransducer 3. Receiver and 4. Recorder

5. Basic components of echo sounder

6. Transmitter High voltage electric pulses of pre-determined frequency are generated in the transmitter . The design of the transducer determines the frequency desired.

7. Transducer This converts the electrical energy to sound in water and conversely The sound waves of the returning echoes are converted back to electrical energy. Sound waves travel through the water at 1,500 m/sec and reflect back as echoes from the objects like bottom, fishes, etc. And strikeback the transducer fitted to the hull.

8. Receiver The weak electrical oscillations produced in the transducer are amplified by the receiver and fed to the recorder for display . Recorder Recorder displays the echoes on the paper recorder, flash light display, an oscilloscope (cathode ray tube or CRT) or an audible signal. The recording unit also has the function of starting the transmitter and of measuring the time between the transmission of sound pulse and the reception of echo.

9. Cathode ray tube or CRT CRT is an electronic device used to display fish echoes. It consists of a cathode ray tube having chemically treated glass screen . The echo signals are presented as luminous glow on the face plate of the scope Certain extra functions can be added to the echo sounder like scale expansion units and bottom lock on oscilloscope (CRT) which help in studying various areas of the seabed and midwater regions with better display of echoes . They are either midwater expansions or seabed locked scale expansion units. Midwater expansion helps in displaying selected water column depth in an expansion unit and is used in larger deep sea bottom trawlers. To study the layer immediately above the bottom on a large scale.

10. Controls in Echo sounder Various controls are provided in an echosounder for its efficient functioning. On-off switch is provided either to put the instrument ready for use or it also does the additional work of starting in smaller types. Marker switch is a push button switch used to plot the reference line on the recorder paper . Range switch selects the range of sounding. Range is selected in such a way that the sea bed line is traced somewhere below the middle of the recording paper. White and grey line display is to differentiate between the weak fish echoes from strong bottom echoes. This is done by a special signal treatment in a receiver whereby echoes above certain strength either completely block the receiver (White line) or are presented as a faint grey recording (grey line). Paper speed and stylus speed should be adjusted to prevent overprinting lines and to comply with the value given by the manufacture respectively.

11. SONAR Sonar is an abbreviation for sound navigation and ranging. The principle of sonar is essentially the same as the principle of echosounder . The difference is that while the transducer of echosounder operates vertically, the sonar transducer operates horizontally or in any lateral direction. The Sonar is capable of producing pulses of different duration. The observation of echoes is carried out in 3 different methods, the paper recording, the cathode ray scope and the aural system (listening).

12. Basic components of Sonar

13. Components of sonar The main components of sonar are the transmitter, the transducer, the receiver and the recorder . Electric pulses of different frequencies, length and power are generated in the transmitter and passed on to the transducer. The transducer converts the electrical energy to sound in the water and the sound waves of returning echoes are converted back to electrical energy. The transducer is mounted on gimbals. The receiver amplifies the weak signals received from fish to the transducer. The receiver amplifies the weak signals received from fish to the transducer. The recorder amplifies the weak signals paper as well as coordinates the operations of transmitter, receiver and transducer to ensure precision and correct sequence in their functions . The display of an approaching fish school appears as a slanting line on the sonogram as the distance changes. This is because of horizontal ranging of the sounder. Indication on a CRT is a better display to record the distance and direction of fish

14. Types of Sonar Two types 1. Search light Sonar 2.Omnisonar Search light sonar Search light sonar, as the name implies are designed to transmit a sound pulse on a selected sector bearing, listen to the echoes and on completion step to a new bearing before transmitting again

15. Search light sonar

16. Omnisonar Omnisonar transmit one sound pulse which effectively radiates from the transducer through a complete 3600 and electronically scan the entire area while listening for echoes. The display shows a complete picture around the vessel for each transmission.

17. Omnisonar

18. Net sonde Net sonde is a type of echo sounder developed mainly to find out the precise position of a pelagic trawl . It also helps to find out the opening of the trawl and records the fish which enter the trawl . It is also useful in bottom trawling for providing as much better estimate of catching efficiency . Net sonde works on the same principle as echo sounder. However , the transducer is fitted to the head rope of trawl net. The transducer is connected to the recording units on the vessel either by a separate cable or by wireless synchronization system.

19. Two types of Net sonde 1. Acoustic link transducer 2. Cable link transducer

20. Acoustic link transducer Two transducers are fitted to the head line in such a manner that one transducer ( sounding transducer) faces down the bottom while the other transducer(transmitting transducer) faces the receiving transducer towed from the vessel. The receiving transducer is connected to the recording unit. The transducer works when it is lowered under certain minimum depth. The vertical transducer transmits ultrasonic sound signals and receives the echoes. These echoes are received and amplified in the transmitter and relayed by the transmitting transducer to the receiving transducer towed by a vessel from cable. The received signals are amplified in the receiver and displayed on the paper in the recording unit.

21. Conti.. A major advantage of this form of net sonde is that there is no need for costly vessel-mounted winch and connecting cable. However , one major disadvantage is that slight misalignment in the initial fitting of the head line unit can cause loss of data link especially when a vessel makes a change of course. The head line unit also relies on batteries for its power which calls for operator’s attention at frequent intervals.

22. Acoustic link transducer

23. Cable link transducer In this, the transducer on the head of the trawl is linked to the towing vessel by a cable and winch arrangement. The transducer cable winch has a release mechanism which will pay out more cable before the cable breaks in the event of sudden increase in tension. Extra expenses for which and cable are a major drawback. Whereas the acoustic link transducer is successful in medium depth and under good alignment and low noise conditions, cable link transducer is preferred for greater depths and unfavourable conditions .

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