C-Max CM2 User manual

USER
MANUAL
The CM2
SIDESCAN
SONAR
SYSTEM
(All configurations except
those using MaxPro software)
Issue 3.6
© C-MAX Ltd 2008

CM2 Sidescan Sonar User Manual
Version 3.6 (2008) ii

CM2 Sidescan Sonar User Manual Contents
CONTENTS
(also see Bookmarks if viewing PDF version)
1. Summary of Warnings ………… 1
2. System Components ………… 2
Towfish
Sonar Transceiver (STR)
C-Shell
C-Case 2
C-Case SE
Tow Cables
Accessories
Specifications
3. Installing the System ………… 6
Data Acquisition Subsystem
Tow Cable
Installing a Winch and Pulley (if used)
Securing the "soft" Tow Cable (if used)
Attaching the Towfish
Checking System Operation
Spares and Tools
4. Planning the Survey ………… 11
Survey Plan
Line Spacing
Line Direction
5. Operating the Towfish ………… 13
Pre-launch Check
Launch
Flying the Towfish
Recovering the Towfish
Action if the Towfish Fouls
6. Operating Guidelines ………… 16
7. Notes for the Helmsman ………… 17
Navigation
Steering
Emergency Actions
8. Towfish Commands ………… 18
Towfish Command Set
Bottom-tracking, Up and Down
Mute, On or Off
Shallow Mode, On or Off
Gain Hold, On or Off
Gain, Up or Down
9. Interpreting the Sonar Image ………… 19
Water Column and Bottom Image
Highlights and Shadows
Image Corrections
Causes of Image Defects
10. Routine Maintenance ………… 21
Routine Maintenance
Replacing the Towfish Breakable Washer
11. Storage and Transit ………… 22
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CM2 Sidescan Sonar User Manual Contents
12. Repair and Replacement ………… 23
Replacing the Towfish PCB
Replacing a Transducer
Repairing the Tow Cable
Replacing the Safety Lanyard
Servicing the Surface Electronics
Servicing the STR
Servicing the C-Shell
Servicing the C-Case 2
Servicing the C-Case SE
13. Troubleshooting ………… 26
14. Interfaces ………… 28
Towfish/Tow Cable
STR
C-Shell
C-Case 2
C-Case SE
15. Specifications ………… 30
Towfish
STR
C-Shell
C-Case 2
C-Case SE
Tow Cables
(Sections 16-22 cover optional accessories)
16. CM2-WIN-300 Winch ………… 33
17. SK172 and SK172E Winches ………… 37
18. Wing Depressor ………… 39
19. Pulleys and Counting Pulleys ………… 41
20. Polemount Bracket ………… 43
21. USBL Transponder Bracket ………… 44
22. Towfish Sensors ………… 45
23. ROV and AUV Configurations ………… 47
24. Warranty ………… 48
Scope
Limitations
Fault Reporting
Returns
Transferability
Version 3.6 (2008) iv

CM2 Sidescan Sonar User Manual 1. Summary of Warnings
1. SUMMARY OF WARNINGS
The warnings summarised here are intended to prevent injury to personnel and equipment in what can be a
hazardous environment.
OPERATORS OF THIS EQUIPMENT ARE RESPONSIBLE FOR THEIR
OWN SAFETY
THE SUPPLIER ACCEPTS NO LIABILITY FOR THE CONSEQUENCES OF
EQUIPMENT USE OVER WHICH IT HAS NO CONTROL
THE GROUND VOLTAGE LEVEL OF ANY EXTERNAL EQUIPMENT,
INCLUDING NAV DATA SOURCES OR ECHO SOUNDERS, MUST BE
CHECKED BEFORE CONNECTION IS MADE TO THE SERIAL PORT OF
ANY ACQUISITION PC OR C-CASE. THE GROUND LEVELS MUST BE
EQUAL OR FLOATING; IF NOT THEN THE INTERNAL CPU PCB MAY BE
DESTROYED (AND DAMAGE SO CAUSED IS NOT COVERED BY
WARRANTY)
DO NOT ALLOW THE TOWFISH TO STRIKE THE BOTTOM OR
OBSTRUCTIONS; THE TOWFISH SINKS WHEN THE BOAT TURNS OR
SLOWS
USE GLOVES TO HANDLE ALL STEEL-ARMOURED TOW CABLES
NEVER ALLOW SLACK IN THE CABLE WHILST THE TOWFISH IS
DEPLOYED
DO NOT EXPOSE THE TRANSDUCERS TO HEAT FROM STRONG
SUNLIGHT
ENSURE THAT ALL ELECTRONIC UNITS ARE DRY BEFORE STORAGE
Version 3.6 (2008) 1

CM2 Sidescan Sonar User Manual 2. System Components
2. SYSTEM COMPONENTS
Towfish
The towfish is the acoustic sensor head. It transmits a very high frequency acoustic pulse (“ping”) at regular
intervals and receives the series of echoes that result from each ping.
Towfish and Tow Cable Terminator
Three types of CM2 towfish are available, namely DF (325/100kHz), EDF (325/780kHz) and HF (325kHz
only). All are identical externally. These are digital towfish, communicating with the surface electronics via
the tow cable.
Optional additional sensors for the towfish are described in Section 22.
Sonar Transceiver (STR)
The “top end” (i.e. surface electronics) unit provides power for the towfish via the tow cable, receives the
echo data and other information such as the towfish altitude, and sends commands to the towfish. The
primary type of top end unit for the CM2 system is the Sonar Transceiver (or STR). As well as
communicating with the towfish, the STR communicates with the PC that acquires, records and displays the
sonar image. Communication with the PC is via the STR’s USB interface.
Sonar Transceiver (STR) Versions
Two versions of the STR exist, differing in the type of connectors used and in the DC voltage range that they
accept. The version fitted with MIL-C-5015 connectors accepts 10-28VDC. The alternative version, identified
by its BNC connector, accepts voltages in the range 10-18VDC, with 24VDC as an ordering option. Early
versions also featured an analog output, generated from the internal digital signal, for driving “legacy”
acquisition systems and thermal printers.
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CM2 Sidescan Sonar User Manual 2. System Components
C-Shell
The C-Shell is an optional polypropylene clamshell enclosure for the STR. The C-Shell converts an STR into
a fully waterproof (IP67) unit, complete with waterproof connectors. The STR can be quickly fitted or
removed.
C-Shell, Panel and Connectors
The C-Shell includes a 4-way USB hub that can be used to house a dongle for the acquisition software. The
C-Shell can also be specified with an integral GPS receiver: the GPS output is fed to the hub for
transmission to the external USB link.
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CM2 Sidescan Sonar User Manual 2. System Components
C-Case 2
C-Case 2 is the first successor to the earlier version that ran MaxPro (under DOS). It is an all-in-one data
acquisition unit with an integral PC, designed for use in the exposed environment of an open boat. It uses
MaxView or third-party acquisition software running under Windows.
C-Case 2, Panel and Connectors
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CM2 Sidescan Sonar User Manual 2. System Components
C-Case SE
The C-Case SE is also an all-weather data acquisition unit. It takes advantage of the availability of
ruggedized laptop PC’s such as the Panasonic Toughbook series to eliminate the need for the under-panel
integral CPU as fitted to the C-Case 2. Like all the later (non-MaxPro) CM2 systems it uses MaxView or
third-party acquisition software running under Windows.
C-Case SE, Panel and Connectors
Tow Cables
The CM2 tow cables use a single pair of electrical conductors to carry both data and power. There are two
types of tow cable offered with the CM2. “Soft” cable is intended for shallow work, where the cable can be
hauled and veered manually. The alternative is steel-armoured cable handled by a winch. Various diameters
of steel-armoured cable are available, the smallest being 4.7mm used on the CM2-WIN-300 winch.
Accessories
Optional accessories including winches, wing depressor, counting pulleys, polemount bracket and USBL
bracket, are described in Sections 16-21.
Specifications
Specifications for the major components and certain accessories are listed in Section 15.
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CM2 Sidescan Sonar User Manual 3. Installing the System
3. INSTALLING THE SYSTEM
Data Acquisition Subsystem
The CM2 system uses a PC, running Microsoft Windows, to acquire and display the sonar records. The user
normally supplies this PC. To install the acquisition software on this PC see the MaxView Installation Guide.
For third-party acquisition software see the supplier's manual.
If the CM2 system uses a Sonar Transceiver (STR) or an STR housed in a C-Shell, link it to the acquisition
PC via the USB cable supplied.
Prepare to apply dc power to the STR. If powering from an AC supply, use the 60W power brick supplied
with the STR.
System with Optional Winch and Counting Pulley
Connect the tow cable or winch signal cable (or “deck” cable) to the STR.
Connect a navigation data cable to the PC if required. As GPS and other sources of navigation data often
output via an RS232 serial connection, and as serial ports are becoming less common on PCs, this
connection may require the use of a serial-to-USB converter. Note that if a CM2 C-Shell (fitted with an STR)
is being used, the GPS data from the C-Shell’s optional internal GPS receiver is already mixed with the
sonar data on the C-Shell’s USB output.
If a counting pulley is to be used, connect its cable to the PC. This may also require a serial-to-USB
converter.
Instead of an STR, some CM2 systems are supplied with all-in-one C-Case 2 or C-Case SE data acquisition
subsystems, with integral PC (C-Case 2) or removable panel-mounted PC (C-Case SE). These require tow
cables and power cables fitted with the appropriate connectors. Interface details are available in Section 14.
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CM2 Sidescan Sonar User Manual 3. Installing the System
Tow Cable
Put adhesive tape markers on the tow cable, a few metres above the terminator, to warn when the towfish is
close to the vessel.
Installing a Winch and Pulley (if used)
The tow cable should run directly from the top of the winch drum to a suitable pulley or fairlead.
Any pulley or fairlead must be no smaller than the cable’s recommended minimum radius, preferably
considerably larger. A pulley is better than a rigid fairlead.
The pulley should normally be suspended above the stern or stern quarter, able to move freely in any
direction, and positioned so that neither the towfish nor the tow cable is in danger of fouling the vessel's
propeller or rudder or any other structure. A central position minimises tow cable heave caused by the
vessel's roll, but may be too close to the propeller wash.
The winch should be mounted as far forward (away from the pulley) as practical, to reduce the maximum off-
axis angle of the cable. Also the winch should be located directly ahead of the pulley to minimize the tilting of
the pulley and side force on the pulley rim. The winch mounting must be able to withstand the shock of the
towfish striking the bottom.
The mounting “footprint” of the CM2-WIN-300 winch is shown in Section 16.
Securing a “soft” Tow Cable (if used)
Make sure that enough cable is flaked out on the deck so that the towfish can reach its operating depth
without the need to disconnect the inboard end of the tow cable. Provide a method of securing the tow cable.
One method is to use a loop of 5-6mm diameter rope, one end secured to the deck and the other terminated
in a “prusik” knot with 2 or 3 turns around the tow cable. The cable will slip through the hitch until the
operator starts to tighten its grip.
To prolong the life of the cable, avoid sharp bends, twisted loops, and shock loads.
Securing a Soft Tow Cable with a Prusik Knot
Attaching the Towfish
Straighten out the end of the tow cable and, if it is a steel-armoured cable, ensure that there is no more than
a half-turn of inherent twist in it.
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CM2 Sidescan Sonar User Manual 3. Installing the System
Attaching the Safety Lanyard and Tow Cable Extension
First remove the drop-nose pin from the rear of the keel, feed the loop of the safety lanyard into the end of
the keel, and replace the pin to secure the loop. Drop the nose of the pin, to 90 degrees, to ensure that the
pin cannot fall out.
Remove the dust cap from the tow cable underwater connector.
Engage the tow cable socket on to the plug on the rear of the towfish, being careful to align the connector
correctly. It is good practice to keep this plug clean and occasionally and only very lightly grease the rubber
sleeves of the pins with the silicone grease provided.
Attach the towing bail using the breakable “safety” washer, and the M6 cap screw with captive washer. Use
the 5mm hex key provided to tighten this screw. The breakable washer is designed to fracture under
excessive load.
The safety lanyard and the tow cable extension should be secured to the left-hand yoke with a 3.5mm cable
tie so that there is no slack in the lanyard and in the tow cable extension between the yoke and the rear fin.
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CM2 Sidescan Sonar User Manual 3. Installing the System
Attaching the Towing Bail
Checking system operation
With the whole system now connected as described earlier in this Section, apply power to the STR, C-Shell
or C-Case. The red Power indicator should light.
If MaxView has been installed, open it and select Start... from the Towfish menu. Alternatively press the
spacebar then select Start Towfish from the Quick Select menu. If some other acquisition software is
installed instead of MaxView, the towfish can be started using that software.
When the towfish is commanded to start, the green Trigger indicator on the STR should light continuously
whilst the Start Towfish dialog displays the Energizing… message. This message should be automatically
replaced after a short period by Connecting…
The Energizing… message indicates that a voltage of approximately 42VDC* is being supplied to the tow
cable connector. This voltage is passed to the towfish to charge its internal capacitors and start its operation.
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CM2 Sidescan Sonar User Manual 3. Installing the System
The Connecting… message indicates that the towfish has started its initialisation and that the tow cable
telemetry is being set up. This message should disappear when the telemetry link has been established and
the towfish has started running.
Note that initially the towfish runs silently, i.e. in the muted mode. This is to allow the telemetry link to
complete its optimisation without any interference from the transducer drive voltage. The muted period lasts
for the first 80 pings.
As soon as the towfish runs the Trigger indicator flashes, once per ping.
Wait for the gain to rise to a point where the “waterfall” display on the screen has filled in to show “noise”
from the environment. At this point the operation of the towfish can be given a basic bench check known as a
“rub test”. Without touching the metal of the towfish with either hand, place one hand briefly on the face of
one of the transducers. This should result in an increase in signal on the appropriate side of the waterfall
display for the time that the hand is that position; at least until the automatic gain control reduces the signal.
Then test the other side in the same way. Note that although this is called a rub test, no rubbing action is
necessary: the signal is induced capacitively, not by mechanical action.
The Quick Select menu, accessed by pressing the spacebar, can be used to change the sonar range and
frequency or to stop the towfish. The spacebar can also be used to clear the Quick Select menu.
(*If the tow cable is higher in resistance than a certain value, the towfish will detect that its internal voltage
has dropped below nominal. In this case it will command the STR, or other unit, to increase its supply to the
tow cable by a further 24V.)
Spares and Tools
Always carry spare breakable washers. A 5mm hex key is the only tool required in normal operation. Every
towfish is supplied with a kit (CM2-TSK) containing minor spares and consumables.
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CM2 Sidescan Sonar User Manual 4. Planning the Survey
4. PLANNING THE SURVEY
Survey Plan
Every survey or search needs to be planned in advance. Survey planning and post-processing are topics
that are wider than can be covered here. Most sonar acquisition software packages, including MaxView,
include the facility to plan survey lines for guiding the helmsman.
Line Spacing
The frequency and range settings should be defined for the type of task being planned, whether it is a search
for a wreck or lost anchor, or a post-dredge clearance check, for example.
The image quality is reduced in the region below the towfish because the image when received is
compressed and also the steep angle results in poorer shadow information. The quality is also reduced at
the extremity of the range primarily because of beam spreading. Survey lines should therefore be spaced
with sufficient overlap (e.g. 75m when working with 100m range setting) to ensure complete coverage.
Overlap is also necessary to compensate for course deviations.
Line Direction
It is normally preferable to run survey lines in the same direction as any current. Where currents are very
strong the lines may need to be run in only one direction, against the stream, as running with the stream
would give too high a speed over the ground thereby reducing the number of pings on any target.
Typical Small Survey; Area Sweep inside a Harbour
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CM2 Sidescan Sonar User Manual 4. Planning the Survey
In order to identify a target, or to provide extra assurance of coverage, it may also be necessary to follow the
along-current lines with a set of perpendicular, cross-current, lines.
Sometimes the major consideration in planning lines is not the direction of the current but the bathymetry. It
is easier to survey along lines of approximately constant depth rather than to be constantly heaving and
veering tow cable to keep the towfish at a suitable altitude.
Finally, the wind direction may be the controlling factor. Waves running across, rather than in the same
direction as, the survey line will cause a spiralling movement of the tow cable and oscillation of the towfish
track. This will have more of an effect on the image than the simple pitching motion if the ship is running into,
or directly away from, the waves.
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CM2 Sidescan Sonar User Manual 5. Operating the Towfish
5. OPERATING THE TOWFISH
Pre-launch Check
Check that the towfish transducers are angled high or low, as required, as indicated by the yellow dots on the
depression adjuster cam.
Adjusting the Transducer Depression Angle
Check that the tow cable connector is firmly home, and that the bail is correctly attached to the towfish.
Check that the tow cable is clear and free from twists, and that the winch is powered and ready to run.
Note that the automatic gain adjustment starts as soon as the towfish is switched on.
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CM2 Sidescan Sonar User Manual 5. Operating the Towfish
Using the Wing Depressor
If the optional wing depressor is used, refer to Section 18 for advice and important warnings.
Launch
Launch the towfish astern with the vessel preferably at slow speed.
DO NOT ALLOW ANY SLACK IN A WINCHED TOW CABLE during launch and whenever the towfish is in
the water. A slack cable can start to wind outside the winch drum. It can also form loops that can pull tight
and SERIOUSLY DAMAGE THE CABLE.
The "soft" tow cable can be handled without gloves but is still capable of giving friction burns if allowed to
slip.
Flying the Towfish
Set the display to show the water column (i.e not slant-range-corrected) then lower the towfish to an altitude
in the range 5-15m initially. The indicated altitude (not necessarily the true altitude at this stage) is shown in
MaxView’s sonar parameters, or equivalent, and may also be also marked on the display by a pair of lines
overlying the initial bottom echoes.
Check that the altimeter is locked on the initial bottom echo, not on the surface echo, nor is left in a “neutral”
position.
IF THE ALTIMETER INITIALLY FAILS TO LOCK ON TO THE BOTTOM CORRECTLY USE THE FORCE
UP – DOWN CONTROL TO PUSH IT INTO LOCK.
Locking the Bottom-Tracking after Launch
In MaxView the bottom-tracking control is Towfish – Bottom-Tracking (or Altimeter in early versions).
The indicated altitude cannot exceed 20m for EF operation, 40m for HF, and 60m for LF. If the towfish is
operated above these maximum altitudes, the image may be degraded; also the altimeter may try to lock on
to surface echo instead of the bottom.
Minimum indicated altitude is 1.4m. MaxView and other acquisition programs may sound an alarm if the
altitude falls below a preset value.
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CM2 Sidescan Sonar User Manual 5. Operating the Towfish
As soon as the altimeter has locked to the bottom and the image is normal, wind the cable in or out, or adjust
speed, until the towfish flies at an altitude equivalent to 5 -10% of the range limit.
The towfish must be flown high enough to clear any obstacles. Over uneven ground, flying high increases
safety and prevents excessive shadowing. Over flat and featureless ground, flying low enhances the
shadows of any object that may be present. In shallow water it may be necessary to fly lower to stay below
the wake.
In very shallow water it may be better to deploy the towfish alongside, or at the bow, rather than astern, but
keep the towfish away from the propeller!
Depending on speed and depth expect to pay out about 3 metres of tow cable for every metre of towfish
depth (not altitude). Always keep a reserve of at least 3 turns of cable on the winch drum.
See Notes for the Helmsman.
Tow in the range 2.5 to 6kt (speed through the water; this may differ from speed over the ground or GPS-
indicated speed). Low over-the-ground speeds give more scans per metre of travel and a correspondingly
better image resolution. Sometimes, however, a higher speed will give a steadier course.
Caution: the towfish will sink towards the bottom whenever the towing vessel slows or turns.
Recovering the Towfish
Slow to 2 to 4 knots before the towfish hits the wake. Watch for the tape marker warning that the towfish is
close.
Wash the towfish, cable and winch with fresh water immediately after use in seawater. When the tow cable is
disconnected from the towfish, cap the cable connector to keep it clean.
DO NOT EXPOSE THE TRANSDUCERS TO HEAT FROM STRONG SUNLIGHT
Action if the Towfish Fouls
If the towfish hits the bottom or other obstruction, the increased towing force will usually break the breakable
washer. The safety lanyard will then apply tension to the rear of the towfish. This will normally cause it to
tumble and to free itself of the obstruction. In the meantime the towing vessel should, of course, slow down
but without going astern into the cable!
Recover the towfish and replace the breakable washer. Inspect the towfish and tow cable for any damage.
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CM2 Sidescan Sonar User Manual 6. Operating Guidelines
6. OPERATING GUIDELINES
Do not allow the towfish to hit the bottom – be very careful when turning
Fly the towfish on as straight a course as possible, to prevent distortion and
smearing of the image
Fly the towfish lower (but safely clear of the bottom) to give best image
shadows, e.g. 5m altitude; fly it higher to give longest effective range, e.g.
10m altitude or more, except in shallow water
Use the higher frequency for best image resolution, and for small targets; use
the lower frequency for longest effective range, and for big targets
Use 10deg transducer depression in normal circumstances; use 20deg
depression if the bottom image is being obscured by reflections from the sea
surface
Higher tow speeds are ok for LF (100kHz) operations, e.g. up to 6 knots
Use lower tow speed for HF (325kHz) operations, e.g. 4 knots
Use lowest tow speed for EF (780kHz) short-range operations, e.g. 3 knots
Low speed gives more “pings” on each target and gives greater towfish depth
for any particular tow cable length
High speed makes it easier to keep the towfish on a straight course
Overlap survey tracks to give best target detection probability; overlap by at
least 2x altitude (approximate rule), ideally 100%
Orthogonal survey tracks (e.g. E-W then N-S) may give more information on
target shape
During the survey always watch the image in NORMAL geometry to check
that the bottom-tracking (automatic altitude measurement) is locked on to the
bottom echo
If the bottom-tracking loses lock use altimeter forcing buttons (up-down) to
restore the correct indicated altitude
Check the incoming nav data and don’t forget to RECORD the sonar data!
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