Patent GB-789225-A (GB)
Title: Submarine echo-sounding apparatus for fishing vessels
Inventor: SCHUTZ PIERRE NICOLAS
IPC: G01S15/96
Filed: 1954-09-27
Abstract: 789,225. Echo-sounding. PYE MARINE, Ltd., and SOC. GENERALE D'ELECTRICITE ET DE RADIO. Sept. 26, 1955 [Sept. 27, 1954], No. 27827/54. Class 118 (2). [Also in Group XL (c)] Echo-sounding apparatus for accurate positioning of a trawl net 5 with respect to a shoal of fish 4 comprises a transducer 9 on the trawl net instead of or in addition to the transducer 8 on the fishing vessel, and means for producing a magnified indication of echoes over a short sounding range, the echoes being indicated on one or more cathode-ray tubes, with a variable frequency oscillator for triggering the pulse transmitter and providing a time-base for the cathode-ray tube (C.R.T.) display. The oscillator frequency is adjusted so that the echo 30 (Fig. 2a) of the sea bed 3 (Fig. 1) occurs at the end of the scanning trace (Fig. 2b), whereby a maximum length of trace is used and the sounding pulse repetition rate is the maximum possible for the depth concerned, the adjustment being effected by a control knob associated with a scale which gives an indication of the depth of the sea bed or other object producing the echo 30 which has been aligned with a fixed mark 32 on the C.R.T. screen. Fig. 3 shows a block diagram of the apparatus. A variable frequency oscillator 15, which provides a time base for C.R.T. 17, triggers pulse transmitter 18, and through a variable delay network 21 synchronizes a high-speed time-base circuit 22. The output from this may be selectively applied to the C.R.T. 17 by the switch 16, or alternatively to a second C.R.T. 23, to provide a magnified partial range of, for example, seven fathoms, selectable within the main range by variation of the delay in network 21. The control knob of the variable delay network 21 is associated with a scale calibrated to indicate the partial range selected. This scale and the sea-bed depth (oscillator frequency) scale may be arranged vertically one on either side of the C.R.T. 17, as in Fig. 6 (not shown). The output of the high-speed time-base circuit 22 is also fed through a pulse-shaping circuit 24 to provide a marker signal for receiving amplifier 20 either to brighten up the trace or displace a portion of it (Fig. 2c), preferably for a duration corresponding to the range of the high-speed time base. The transmitter 18 and receiving amplifier 20 may be connected to the transducer 8 on the ship or to transducer 9 on the net by means of change-over switch 19. When a shoal of fish has been located (e.g. 34 in Fig. 2b) the marker signal is used to determine its depth (Fig. 2c) and the oscillator 15 set to a depth corresponding to the distance between the fish and the sea bed. Using transducer 9 the trawl net is then adjusted to bring the sea bed echo again to the mark 32 when the net will be level with the fish. The magnified partial range may then be used but the delay circuit 21 must be restored to zero in order to show the seven fathoms (including the net opening) below transducer 9. This may be done manually, but is preferably effected automatically upon operation of both switches 16 and 19. Additional contacts 16a and 19a may be used to short-circuit the delay network as shown in Fig. 3. Alternatively, the transmitter 18 could be triggered from the highspeed time-base 22 instead of oscillator 15. A rope 11 (Fig. 1) carrying rings 12 may be arranged across the front bottom edge of the trawl net to produce a strong echo 36 (Fig. 2e). Thus fish being caught are represented at 341 and fish which are not being caught at 34<SP>11</SP>. The transducer 9 may be enclosed in a semibuoyant casing in order not to upset the balance of the net. For fishing in very deep waters the transducer 9 may be arranged to transmit the ultrasonic pulses upwardly and the echo from the surface used as a reference instead of the sea bed. In this case the transducer 9 should be mounted on the bottom of the'net opening. Alternatively the transducer 9 may incorporate two units and be arranged to transmit upwardly or downwardly by selective switch means on board the ship. A detailed circuit arrangement (Fig. 4, not shown) is described (see Group XL (c)). Specification 732,608 is referred to.