Furuno CSH-53 User manual

COLOR SCANNING SONAR
MODEL CSH-53
Back

The paper used in this manual
is elemental chlorine free.
Your Local Agent/DealerYour Local Agent/Dealer
9-52 Ashihara-cho,9-52 Ashihara-cho,
Nishinomi
y
a 662-8580, JAPANNishinomi
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a 662-8580, JAPAN
Tele
p
hone :Tele
p
hone : 0798-65-21110798-65-2111
FaxFax 0798-65-42000798-65-4200
::
F
IRST EDITION :
F
IRST EDITION : JULJUL.. 19971997
Printed in JapanPrinted in Japan
A
ll ri
g
hts reserved.
A
ll ri
g
hts reserved. EE ::MARMAR.. 03, 200503, 2005
Pub. No.Pub. No. OME-13070OME-13070
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(( DAMIDAMI )) CSH-53CSH-53 * 0 0 0 8 0 8 0 7 3 0 1 ** 0 0 0 8 0 8 0 7 3 0 1 *
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13070
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i
SAFETY INSTRUCTIONS
WARNING
Do not open the equipment.
Hazardous voltage which can
cause electrical shock, burn
or serious injury exists inside
the equipment. Only qualified
personnel should work inside
the equipment.
Do not disassemble or modify the
equipment.
Fire, electrical shock or serious injury can
result.
Turn off the power immediately if water
leaks into the equipment or the equip-
ment is emitting smoke or fire.
Continued use of the equipment can cause
fire or electrical shock.
Do not place liquid-filled containers on
the top of the equipment.
Fire or electrical shock can result if a liquid
spills into the equipment.
Do not operate the equipment with wet
hands.
Electrical shock can result.
Keep heater away from equipment.
Heat can alter equipment shape and melt
the power cord, which can cause fire or
electrical shock.
CAUTION
Use the proper fuse.
Use of a wrong fuse can result in fire or
permanent equipment damage.
Do not use the equipment for other than
its intended purpose.
Personal injury can result if the equipment
is used as a chair or stepping stool, for
example.
Do not place objects on the top of the
equipment.
The equipment can overheat or personal
injury can result if the object falls.
Do not exceed speed noted in the speci-
fications when operating the equipment
or lowering or raising the transducer.
The transducer may become damaged.
The zinc block attached near the
transducer must be replaced yearly.
The junction between the transducer and
main shaft may corrode, which can result
in loss of the transducer or water leakage
inside the ship.
WARNING
To avoid electrical shock, do not
remove cover. No user-serviceable
parts inside.
TYPE：86-003-1011-0
CODE No.：100-236-230
TYPE：03-160-1042-0
CODE No.：100-302-750
DANGER
Electrical shock hazard.
Turn off power before
servicing.
WARNING LABEL
Warning labels are attached to the equipments. Do not remove the lables. If the labels
are missing or damages, contact a FURUNO agent or dealer about replacement.

ii
TABLE OF CONTENTS
FOREWORD
AWord to CSH-53 Owners......................................................................................................................v
Features...................................................................................................................................................v
System Configuration.............................................................................................................................vi
SYSTEM CONFIGURATION
Control Layout on Display Unit, Processor Unit and Remote Control Box ............................................1-1
Main Panel ...........................................................................................................................................1-2
Sub Panel 1...........................................................................................................................................1-4
Sub Panel 2 (data setting window) ........................................................................................................1-5
Remote Control Box.............................................................................................................................1-8
OPERATIONAL OVERVIEW
Turning the Power On/Off ....................................................................................................................2-1
Adjusting Screen Brilliance, Control Panel Backlighting.......................................................................2-1
Lowering the Transducer ......................................................................................................................2-1
Selecting a Display Mode .....................................................................................................................2-2
Selecting a Display Range ....................................................................................................................2-3
Setting the Tilt Angle............................................................................................................................2-3
Adjusting the Gain................................................................................................................................2-7
Measuring Range and Bearing to a Target .............................................................................................2-7
FINE TUNING THE PICTURE
Eliminating Unwanted Feeble Echoes...................................................................................................3-1
Suppressing Seabed Tail .......................................................................................................................3-3
Suppressing Seabed and Sea Surface Reflections in Shallow Waters......................................................3-4
Rejecting Sonar Interference and Noise.................................................................................................3-4
MARKS AND DATA
Marks, Data and Display Mode.............................................................................................................4-1
Permanently Displayed Marks and Data................................................................................................4-3
Erasable Marks and Data ......................................................................................................................4-4
MENU OVERVIEW
USER Menu Operation.........................................................................................................................5-1
USER Menu Description ......................................................................................................................5-3
SYSTEM Menu Description.................................................................................................................5-5
DATASET Menu Description...............................................................................................................5-8
INIT SET/TEST Menu Description.....................................................................................................5-11

iii
FUNCTION KEYS
Programming the Function Keys.......................................................................................................... 6-1
Replaying a Function Key.................................................................................................................... 6-2
Function Key Fine Tuning.................................................................................................................... 6-2
Saving Function Key Settings to a Memory Card................................................................................. 6-3
Replaying Function Key Settings from a Memory Card........................................................................ 6-3
ADVANCED LEVEL OPERATION
Finding Fish School Center.................................................................................................................. 7-1
Tracking a Fish School (target lock)..................................................................................................... 7-2
Detecting Fish Schools Aurally............................................................................................................ 7-7
The Fish Alarm.................................................................................................................................... 7-8
Relocating Fish School for Easy Observation....................................................................................... 7-9
Comparing of Fish School Concentration............................................................................................7-10
Measuring Fish School Speed.............................................................................................................7-11
The Event Mark..................................................................................................................................7-12
True Motion Display...........................................................................................................................7-14
Plotting Net Location Mark.................................................................................................................7-15
Observing Net Behavior......................................................................................................................7-16
Reducing Sea Surface Reflections.......................................................................................................7-17
Boosting Tx Power .............................................................................................................................7-17
PORT/STARBOARD, HORIZONTAL SLICE DISPLAYS
Port/Starboard display.......................................................................................................................... 8-1
Horizontal slice display........................................................................................................................ 8-2
SAVING, REPLAYING PICTURE
Initializing Memory Cards................................................................................................................... 9-1
Saving the Picture................................................................................................................................ 9-2
Transferring Echo Data from Internal Memory to Memory Card.......................................................... 9-2
Saving Net Shooting Data.................................................................................................................... 9-3
Replaying Saved Data.......................................................................................................................... 9-4
Deleting Memory Card Contents.......................................................................................................... 9-4
TURNING MARKS, DATA ON/OFF .................................................................10-1
INTERPRETING THE DISPLAY
Seabed Echoes....................................................................................................................................11-1
Fish Schools .......................................................................................................................................11-2
Sea Surface Reflections ......................................................................................................................11-3
Wake ..................................................................................................................................................11-3
False Echo by Sidelobe.......................................................................................................................11-4
Noise and Interference........................................................................................................................11-4

iv
WARNINGS
Overvoltage Warning...........................................................................................................12-1
Unretracted Transducer Warning ........................................................................................12-1
SELF TESTS
Opening the Self Test Menu................................................................................................13-1
Self Test Description ...........................................................................................................13-2
Interface Unit CS-120A Self Test........................................................................................13-5
INPUT DATA SELECTION
Selection of Data at Interface Unit CS-120A......................................................................14-1
Setting Distances Between Net Sonde Transmitters ...........................................................14-2
MAINTENANCE
Display Unit Maintenance...................................................................................................15-1
Hull Unit Maintenance ........................................................................................................15-2
Replacement of Fuse, Memory Card Battery......................................................................15-3
MENU TREE...................................................................................................... A-1
SPECIFICATIONS...........................................................................................SP-1
INDEX .............................................................................................................. IN-1

v
FOREWORD
A Word to CSH-53 Owners
Congratulations on your choice of the FURUNO CSH-53 Color Scanning Sonar. We are
confident you will see why the FURUNO name has become synonymous with quality
and reliability.
For over 50 years FURUNO Electric Company has enjoyed an enviable reputation for
quality marine electronics equipment. This dedication to excellence is furthered by our
extensive global network of agents and dealers.
This equipment is designed and constructed to meet the rigorous demands of the
marine environment. However, no machine can perform its intended function unless
operated and maintained properly. Please carefully read and follow the recommended
procedures for operation and maintenance.
We would appreciate hearing from you, the end-user, about whether we are achieving
our purposes.
Thank you for considering and purchasing FURUNO equipment.
Features
The FURUNO CSH-53 Color Scanning Sonar is a full-circle, multibeam electronic
scanning sonar which detects and instantaneously displays fish schools and underwater
conditions in 16 colors on a 15" non-glare, high resolution CRT screen.Also, the CSH-53
has two types of models: a model with display unit and a model with processor unit and
no monitor (monitor is supplied by user).
The main features of the CSH-53 are
• Vivid 16-color display provides intuitive recognition of seabed and concentration,
distribution and volume of fish schools.
• Markers and indications keep the operator abreast of fishing conditions.
• Remote control box provides for armchair control of major functions.
• New gain, range or tilt setting appears in large characters whenever corresponding
control is adjusted.
• Function keys automatically setup the equipment to perform specific task.
• High power MOS FET transmitter ensures reliable operation under any condition.

vi
System Configuration
STANDARD OPTION
REMOTE CONTROL BOX
CSH-135 DISPLAY UNIT
CSH-530
MONITOR (MU-151C)
or
COMMERCIAL MONITOR
SUB DISPLAY
CSH-536
STEP-DOWN
TRANSFORMER
PT-400
INTERFACE UNIT
CS-120A
VI-1100A
FNZ JOINT BOX
CS-170
TRANSMITTER UNIT
CSH-551
SHIP'S MAINS
100 VAC, 1
φ ,
50/60 Hz
110/115/220/230 VAC,
1
φ , 50/60 Hz
SPEED LOG
NAVIGATOR
CURRENT INDICATOR
COLOR VIDEO SOUNDER
AD CONVERTER
ECHO SOUNDER, COLOR
VIDEO SOUNDER
NET SONDE
SHIP'S MAINS
100 VAC, 1
φ ,
50/60 Hz
or
PROCESSOR UNIT
CSH-535
INTERFACE UNIT
HULL UNIT
(w/RECEIVER UNIT) CSH-552
CSH-5508 (800 mm stroke)
CSH-5512 (1200 mm stroke)

1-1
CONTROL DESCRIPTION
Control Layout on Display Unit, Processor Unit and
Remote Control Box
POWER TRANSDUCER
OFF ON
F1 F2 F3
-
+
NORM E/S HIST RECALL MEMO
NARROW
SHOOT R/B
- +
- +
RANGE GAIN
AUTO
TILT
WIDTH
TILT
SCAN DEPTH
DIM CONT BRILL AUDIO
NET
COURSE TARGET LOCK
EVENT1 EVENT2
ESTI-
MATE1 ESTI- MATE2
FISH OFF-
CENT
PUSH-OPEN
BOOST
Same as Sub-panel
of the display unit
*: The contrast and billiance
controls are disable. Adjust
them at a monitor.
+-
+-
+-
+-
+-
+-
DISP
POWER TRANSDUCER
OFF ON
F1 F2 F3
-
+
NORM E/S HIST RECALL MEMO
NARROW
SHOOT R/B
- +
- +
RANGE GAIN
AUTO
TILT
WIDTH
TILT
SCAN DEPTH
DIM CONT BRILL AUDIO
NET
COURSE TARGET LOCK
EVENT1 EVENT2
ESTI-
MATE1 ESTI- MATE2
FISH OFF-
CENT
BOOST
SUB PANEL 1
MAIN PANEL
SUB PANEL 2
*
Display unit Processor unit
123
DISPSELECT DATA
EVENT TGTLOCK
ESTIMATE
1
NETCOURSE
FISH
OFF-
CENT
TX
1234
FUNCTION
5
+
RANGE
+
GAIN
SHOOT MEMO
RECALL
AUTO
AUTO
BOOST TILT
TRAIN
SCANDEPTH
-
-
NARROW
Selects which display unit to control
in multiple display unit installation.
Raises/lowers the transducer.
: Raises transducer.
: Mid protrusion
: Full protrusion
Press to enter mark shown on key
or shift screen center.
Selects display range.
Adjusts receiver sensivity.
Not used.
Each press displays water
temperature or depth at screen
center for about five seconds.
Turns on transmitter.
Shifts trackball mark.
Replays user preset settings.
Lit lamp shows current selection.
Displays net shooting mark.
Saves picture to memory card.
Sharpens width of Tx beam.
Automatically tillts sounding
beam in 2°steps within tilt
angle selected by WIDTH key.
Varies the tilt angle of the
sounding beam between -5°
and 60°.
Changes weight in vertical
direction at Tx.
Replays a stored picture.
Remote control box
Figure 1-1 Display unit, processor unit and remote control box

1-2
Main Panel
POWER TRANSDUCER
OFF ON
F1 F2 F3
-
+
NORM E/S HIST RECALL MEMO
NARROW BOOST
SHOOT R/B
- +- +
RANGE GAIN
AUTO
TILT
WIDTH
TILT
SCAN DEPTH
DIM CONT BRILL AUDIO
NET
COURSE TARGET LOCK
EVENT1 EVENT2
ESTI-
MATE1 ESTI- MATE2
FISH OFF-
CENT
Figure 1-2 Main panel
Main panel control description
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1-3
Control Function
NORM, E/S, HIST
(Mode keys) Select display mode: NORM, normal sonar picture; E/S, Echosounder combination; HIST, Historical display.
Lamp above a key lights to show current selection.
RECALL, MEMO RECALL: Replays saved picture.
MEMO: Saves picture to memory card or internal memory.
RANGE Selects a picture display range. Range selected appears on the display.
GAIN Adjusts receiver sensitivity.
NARROW Sharpens width of Tx beam when turned on (light above key is on).
The off position provides normal Tx beamwidth.
BOOST Changes weight of vertical direction during transmission when turned
on.
SHOOT Press when net is cast. The net shooting mark, *net sonde marks and
*current mark appears at the own ship mark. The net shooting mark,
net sonde marks and current mark moves on the *ship's track as the
ship moves. The lamp above the switch lights and time *distance run
appear on the display unitl the net shooting mark is turned off.
(* Requires external sensor.)
R/B Provides range and bearing data from own ship to a target. Select
target with trackball and then press the R/B key. A line connects
between own ship mark and trackball mark to measure bearing.
TILT Changes the tilt angle of the sounding beam between -5°and 60°.
AUTO TILT Automatically tilts the sounding beam up and down in 2°steps within
the tilt angle selected by the WIDTH key. The lamp above the key
lights when automatic tilt is on.
WIDTH Sets tilt width in automatic tilt.
NET COURSE Marks location of net.
TARGET LOCK Tracks a fish school.
EVENT 1, 2 Inscribes event mark on the display, to find horizontal, range, depth
and bearing of a target.
ESTIMATE 1, 2 Compares volume of two fish schools.
FISH Measures fish school speed.
OFF-CENT Relocates selected target.
DIM Adjusts the backlighting of the control panels and the brightness of
the lamps above keys
CONT Adjusts screen contrast.
BRILL Adjusts screen brilliance.
AUDIO Adjusts volume of built-in loudspeaker, which monitors a target
appearing along the bearing marker.
TRACKBALL Follows on-screen movement of trackball mark, to enter marks and
off-center the screen.

1-4
Sub Panel 1
RECALL MEMOHISTE/SNORM
F4 F5F3F2F1
ON
OFF
POWER TRANSDUCER
CARD
REPLAY COLOR NET
REPLAY TX
HELP
END
MENU
Figure 1-3 Sub panel 1
Sub panel 1 control description
Control Function
MENU Opens/closes the menu.
END • When the menu is displayed it terminates menu operation and
returns control to the sonar picture.
• When in a sub menu it returns to previous sub menu.
HELP Provides operating information for current menu.
cd[ \ Select items on menus.
CARD REPLAY Replays card-stored control and menu settings.
COLOR Changes display color among four choices.
NET REPLAY Replays internally stored net shooting data. To replay, press key to
light lamp above it, select item to replay, and press the key again.
TX Press to transmit, when transducer is lowered. Lamp lights during
transmission.

1-5
Sub Panel 2 (data setting window)
SIGNAL
DELETE MK
ES
SONR
Q
BEAM
AUTO
ALM
Q
AUDIO
NEAR
7
MEDIUM
8
FAR
9
CYCLE
7
PL
8
OUTPUT
9
TVG TX
+ + + + + +
- - - - - -
OPER
P-SET
(TOGGLE)
Setting change keys
Change control setting.
Item selection keys
Select item.
OPER P-SET key
Opens/closes data setting window.
ITEM
(TVG
Q
TX selected)
CURRENT SETTINGS for item selected (TVG
Q
TX)
This example shows settings
of TVG and TX.
TVG
Q
TX
Figure 1-4 Sub panel 2
Note: The sub-panel 2 for the processor unit is arranged vertically.
Sub panel 2 control description
Item
Main
Item Main Sub
Setting
Range Description Normal Setting
NEAR 0-9
Adjusts receiver gain within
100 m. 5
MEDIUM 0-9 Adjusts receiver gain between
100 m and 400 m. 5
TVG
FAR 0-9
Adjusts receiver gain beyond
400 m. 5
CYCLE 0-9
Sets Tx cycle. 9 is normal setting
(fastest). “0” synchronizes with
external KP.
9
PL 0-9
Sets Tx pulselength. 9 is normal
setting. 9
TVG ●TX
TRANSMIT
OUTPUT 0-9 Sets Tx output power. 9 is
maximum power. 9
(Continued on next page)

1-6
Main
Item Item Setting Range Description Normal Setting
Main Sub
SIGNAL
SIGNAL
PROCESS
NL 0–10 Rejects unwanted echoes. 3
AGC 0–10
Automatically reduces receiver
gain against strong echoes such
as seabed. Adjust so fish echo is
displayed near seabed.
0
2AGC* 0–4 Suppresses seabed echoes. If AGC alone cannot suppress
seabed echoes, use 2AGC. 0
SIGNAL
PROCESS
CURVE 1–4
Selects echo level versus presen-
tation color curve. The higher
the setting, the easier it is to see
weak echoes on the screen.
2
IR 0–3 Rejects random noise and inter- ference by other echo sounders
or sonars. 0
AFGLOW 0–4
Adjusts echo afterglow, which is
useful for watching echo move-
ment. The higher the setting the
longer the afterglow remains.
0
ES
ES1
(Net
Recorder)
RANGE
(DN RNG) 16 Pos.
Sets depth range of echo
sounder picture. Sets range of
net recorder downward
sounding.
160 m
GAIN 0–10 Adjusts receive sensitivity. 5
SHIFT
(UP RNG) 0– 1000 m
Sets display start depth of echo
sounder picture. Sets range of
net recorder upward sounding. 0 m
ES1
(Net
Recorder)
NL 0–10 Rejects blue dots (caused by
dirty water) on entire screen. 0
COLOR 0–9 Eliminates echoes displayed in
colors specified. 0
IR ON,
OFF Eliminates interference by other sonars or echo sounders. OFF
DELETE MK
DELETE
MARK + or -
key to
erase.
Each pressing erases oldest mark
among event mark 1, event mark
2, fish mark, own ship mark.
DELETE
MARK TRACK Each pressing deletes 1/5 of
overall length.
*2AGC and HOR functions cannot be used together. If one is used the other is
automatically set to “0”.
(Continued on next page)

1-7
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*HOR and 2AGC functions cannot be used together. If one is used the other is
automatically set to “0”.

1-8
Remote Control Box
123
DISPSELECT DATA
dc d
EVENT TGTLOCK
ESTIMATE
1NETCOURSE
FISH OFF-
CENT
TX
1234
FUNCTION
5
–
+
RANGE
+
–
GAIN
SHOOT MEMO
NARROW RECALL
AUTO
AUTO
BOOST TILT
TRAIN
SCANDEPTH
Each press displays water
temperature or depth at screen
center for about five seconds.
Turns on transmitter.
Shifts trackball mark.
Replays user preset settings.
Lit lamp shows current selection.
Displays net shooting mark.
Saves picture to memory card.
Sharpens width of Tx beam.
Replays a stored picture.
Varies the tilt angle of the
sounding beam between -5°
and 60°.
Automatically tillts sounding
beam in 2° steps within tilt
angle selected by WIDTH key.
Changes weight in vertical
direction at Tx.
Not used.
Adjusts receiver sensivity.
Selects display range.
Press to enter mark
shown on key or shift
screen center.
Raises/lowers the transducer.
c: Raises transducer.
d: Mid protrusion
d: Full protrusion
Selects which display unit to
control in multiple display unit
installation.
Figure 1-5 Remote control box

2-1
OPERATIONALOVERVIEW
Turning the Power On/Off
Turning the power on
Press the ON switch on the main panel. The lamp above the key
should light. If it doesn’t press the TX switch on sub panel 1.
Turning the power off
Retract the transducer with the cswitch and then press the OFF
key on the main panel.
Note:Thetransducer isautomatically retracted intothe tankeven
if the OFF switch is pressed before retracting the transducer.
However, make it a habit to retract the transducer before turning
off the power.
Adjusting Screen Brilliance, Control Panel Backlighting
The BRILL control adjusts screen brilliance, and the DIM con-
trol adjusts control panel backlighting. These controls are on the
lower part of the main panel.
Lowering the Transducer
Press dor dswitch. The lamp above the
keyblinks duringlowering ofthe transducer
andlights whenthe transduceris completely
lowered.In normaluse fullylowerthetrans-
ducer. The transducer extends 1200 mm
below the ship’s hull, providing stable and
cavitation-free soundings. If the transducer
may become entangled in the net, after
shootingthenet, forexample, partiallyraise
thetransducer withthe dswitch.Thisraises
the transducer by 400 mm (transducer ex-
tends 800 mm from ship’s hull).
CAUTION
Do not exceed speed noted in the speci-
fications when operating the equipment
or lowering or raising the transducer.
The transducer may become damaged.
Do not press the cswitch during
lowering of the transducer, and do not
press the d or dswitch during raising
of the transducer.
The equipment may become damaged.

2-2
Selecting a Display Mode
The CSH-53 provides three display modes: normal sonar pic-
ture, echo sounder combination, and history display combina-
tion. Those modes may be selected with the NORM, E/S and
HIST keys.
Table 2-1 Display mode description
Mode Description
The sonar picture appears over the entire screen.
This mode is useful for detecting and tracking fish
schools.
The default display area is 1.3 times
the range, but it can be changed to
1.6 times the range on "EXT KP/TM
DSP" in the SYSTEM menu.
Navigation information can be
displayed in the text window at
the screen bottom by turning on
"DATA DISPLAY" in the user
menu.
Normal scanning picture appears on the upper 5/8
of the screen and the signal fed from the echo
sounder on the lower 3/8. This mode is suitable for
judging fish school concentration.
When two echo sounders are connected, each
pressing of the E/S key alternately selects echo
sounder 1 or echo sounder 2.
Note that a net recorder can be connected as echo
sounder 2; select it on the "ES" sub menu in the
INIT SET/TEST menu.
Normal scanning sonar picture appears on the upper
5/8 of the screen and the history display on the
lower 3/8. Three types of history displays are
available: Audio, Port/Starboard and Horizontal
Slice. You can select which one to display on the
USER menu.
NORMAL
E/S
HISTORY
Text window

2-3
Selecting a Display Range
Operate the RANGE control to select a display range.The range
selected appears at the top center of the screen.
Setting the TiltAngle
The tilt angle shows the direction to which the sound wave is
emitted. When the sound wave is emitted horizontally, the tilt
angle is said to be zero degrees and when emitted vertically, 90
degrees.
To set a tilt angle, operate the TILT lever.
Watch the tilt angle indication at the top right
corner on the screen. The tilt angle can be set
in one-degree steps from -5°(upward) to 60°
(downward).
Finding a proper tilt angle is important when searching for fish.
Below are tips for selecting tilt angle.
Seabed echo and tilt angle
Case 1: Tilt angle 30 to 40 degrees
This tilt angle will display the entire seabed since it is captured
by the full width of the beam.
Case 2: Tilt angle 10 to 20 degrees
This tilt angle will only display half the seabed since it is only
captured by the lower half of the beam.
Case 3: Tilt angle 0 to 10 degrees
This tilt angle may or may not capture the seabed since the re-
turning echo is weak.
R400
T 15
Tilt
angle

2-4
How to discriminate fish echoes from the seabed
The figure below illustrates how two fish schools aand b are
displayed on the screen using three different tilt angles.
Case 1: Tilt angle 30 to 40 degrees. Fish school is obscured by
the seabed.
Case 2: Tilt angle 10 to 20 degrees. Fish school is located above
the seabed (midwater).
Case 3: Tilt angle 0 to 10 degrees. Fish school is located close to
the seabed.
Case 1 Case 2 Case 3
Fish school a
Seabed Fish
school b
Case 3
Case 1 Case 2
Fish school aFish school a
Seabed Seabed
Figure 2-1 Fish echo and tilt angle
Points to consider
• Normally, a vertically distributed fish school is a better sonar
target than the seabed, because it reflects the transmitted pulse
back toward the transducer.
• In case 3, both fish schools aand b are presented. Gener-
allyspeaking,however, midwaterfish schoolstendto belarger
than bottom fish schools and they are often displayed near the
seabed on the display.
• It is difficult to detect bottom fish when they are not distrib-
uted vertically.