C-MAX is a leading supplier of professional sidescan systems. The CM2 Sidescan Sonar System is noted for its performance and its robust, user-friendly design. The CM2 is supported by a complete range of accessories, including the portable winch, to aid the surveyor’s task.
CM2 digital sidescan sonar systems are in use all over the world in a wide variety of applications.

Key Features
  • High definition images
  • Flexible system configurations
  • Ease of use
  • Robust build
  • 3 year warranty
CM2 Digital Towfish

The CM2 family of towfish includes two versions, the Standard and the DeepTow. Each version incorporates dual frequency operation, with a choice of two configurations, DF (100/325kHz) and EDF (325/780kHz).
For general survey tasks DF towfish are often the most useful. In 100kHz mode the search swath is up to 1000m wide, useful for searching for larger objects such as wrecks or freight containers. In 325kHz mode it is usually possible to distinguish such objects as mooring ropes, anchor chain, anchors, scour marks, pilings, crab pots, rocks (down to the size of a briefcase or less), as well as differences in seabed texture.
The CM2 Standard towfish.
EDF towfish offer the highest resolution. Like the DF towfish they offer 325kHz operation out to 150m. The EDF’s 780kHz frequency gives the most detailed images, very useful for positively identifying an object first located at 325kHz.
The choice between Standard and DeepTow versions depends on the intended typical working depth and on the size of the towing vessel. Both versions are rated to 2000m but the Standard towfish can be launched and recovered by one man and is the first choice for any work down to a 100m depth, particularly from survey launches or similar small boats.
The CM2 DeepTow towfish.
The DeepTow, with its extra weight, is designed for use on larger survey ships, typically in conjunction with long, larger diameter tow cables.

Note that the complex HF sonar transducer configuration in both types of towfish is unique to C-MAX. It produces powerful, flat-topped transmit and receive beams complemented by additional coverage below the towfish. This gives wide high quality images and enhanced immunity from surface reflections.
C-MAX’s unique towfish beam pattern
All of the towfish models feature:

Digitally controlled dynamically-optimised gain profile
Automatic towfish altitude measurement
Seabed proximity alarm
Breakaway mechanism with a safety link
Adjustable depression angle for the transducers
Water temperature sensor

CM2 Acquisition and Imaging

The CM2 Sonar Transceiver unit
The Sonar Transceiver (STR) interfaces the towfish to an external data acquisition computer via a USB link. It makes the sonar appear to the computer as a USB peripheral and also powers the towfish.

The STR integrates seamlessly with C-MAX’s MaxView acquisition software or can also be used with acquisition software from other leading manufacturers. Please see the Software section of the site or contact us for more information.
The C-Shell waterproof enclosure
The C-Shell provides a rugged operating enclosure for the STR, waterproof to IP67. This enclosure is ideal for open boat use and is available with an integrated GPS.

CM2 Cables and Winches

The CM2’s telemetry is so versatile that it can handle coaxial or twisted pair cables from 50m up to 6000m long. CM2 tow cables carry both power and signal on a single pair of conductors enabling both coaxial or twisted pair cables to be used with no user modifications required when switching cable types.
C-MAX can supply a range of winches and cables from 50m kevlar armoured coax suitable for shallow water surveys to 1000m of steel armoured twisted pair on an electric winch.

The CM2 portable winch and 4.7mm cable

The CM2 portable winch with 300m cable capacity can be hand carried to the survey vessel and features:

Only 47kg with 300m of cable
All stainless steel construction
Maintenance free, fully sealed mercury sliprings
Built in overload clutch
Soft-start feature gives smooth cable handling

The CSW-7 Electric winch from AGO Environmental Electronics Ltd.
For larger cables up to 1000m in length, the CSW series winch from AGO Environmental Electronics is usually specified.

These winches feature:

Robust powder coated frame
Level wind facility
Choice of AC or 24v DC power
Compact footprint
For more details please contact AGO Environmental Electronics

Important information about towcable selection

It can be assumed, as a “rule of thumb”, that the length of tow cable required for a sidescan sonar towfish is about 3 times the depth of the towfish. This is because the drag on the tow cable causes it to lie at an angle astern. A normal towing altitude for the towfish is between 5 and 20m metres above the seabed.
For search depths down to approximately 40m the ‘soft’ kevlar/coax (CX) cable may be used, but, because the cable is light, it will drag out to a shallower angle astern than steel-armoured tow cables for the same speed. CX cables are available in 50m and 100m lengths, plus longer options to special order.
For search depths covering from very shallow down to 80-100m the 4.7mm (LOG5) cable on the CM2 winch is a convenient option.
To reach deeper tow depths this LOG5 cable can be used on a larger winch. If the required depths increase even further, a heavier armoured tow cable with a diameter of 8.2mm or 11.4mm is normally needed.

CM2 Accessories

The Towfish wing depressor
The CM2 Wing Depressor is an optional towfish attachment. It provides extra downforce to combat the drag of the tow cable, allowing the towfish to run deeper.
The wing, with clip-on tail, adds only 5kg to the launch weight; and recovery is aided by the wingtip handles. The efficient, high-aspect-ratio design of the wing allows it to generate 18kg of hydrodynamic downforce at 4kts. Download the specification here to see the effect that this has on the towfish depth.
This wing is significantly more efficient hydrodynamically than the V-fin type of depressor. It also does not suffer from the instability of the V-fin on launch. [Note that it is the unique design of the CM2 towfish, with its rear-mounted transducers, that allows an underslung wing to be used without interference with the acoustics; traditional towfish configurations are restricted to a top-mounted V-fin depressor.
The wing clamps to the towfish using four screws. Attaching and detaching is a 2-minute job.
The CM2 Counting pulleys, standard and large types
Whilst it is possible to use a pulley or fairlead which may be already available on the survey vessel, it is normally better to use a purpose-designed pulley.
The advantage of using a C-MAX Counting Pulley is that the amount of tow cable paid out is continuously displayed to the sonar operator. This allows the operator to make estimates of layback (the horizontal distance of the fish behind the navigation reference point), to assess the vulnerability of the towfish to changes in ship speed, and to monitor the operation of the winch if it is being controlled by a deck crew.
The pulleys feature a quick release ‘snatch block’ configuration which allows simple fitting of the cable with no loose parts to get dropped.
The Counting Pulley includes a counting module with a PC-compatible RS232 link. The link transmits measured length in metres or feet, up to +/-10000m [32800ft]. Measurement resolution is 0.5 metre [1.7ft]. No batteries are required as power is extracted directly from the link. The standard link length is 10m [33ft] and other lengths are available to order.
The pulley is also available without the counting facility if required.

Pole mount

The Pole Mount allows the user to easily attach the towfish to a 50mm (2 inch) diameter pole for overside deployment in shallow water depths and is of stainless steel construction.
Please note that a suitable pole is not included.
Towfish transit case
A purpose-designed clamshell transit case is available for the CM2 Towfish.
Cases are also available for the CM2 Winch and Wing Depressor