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英國C-MAX Ltd
英國C-MAX CM2型側掃聲納

C-MAX Ltd is based in Dorset, England and was established 16 years ago to develop and manufacture innovative sidescan sonar systems.

The term 'sidescan' refers to the simple fact that this type of sonar looks to both sides rather than looking forward, and forms the image by physically moving the sonar head - the towfish - over the seabed. No other type of sonar can give such an easily interpreted picture of the seabed and objects on it.

Starting with the CM800 in 1994, and continuing with the CM2 in 2002, there are now over 300 systems deployed worldwide.

All C-MAX systems and equipment are designed by C-MAX staff. As well as the hardware, the display, recording and towfish software is also all designed in-house. If you talk to C-MAX staff you are talking to the people who really know the sidescan sonar they have supplied.

We are located only a few miles from the coast, and our boat is based in Weymouth Harbour. We are fortunate in being able to test our sonars off the nearby Portland Harbour, an area with a variety of seabed textures, breakwaters, wrecks and other sonar targets. Every sonar that leaves our factory has been tested at sea.

C-MAX Ltd was founded in 1992. In 1994, we introduced the CM800 system and more than 100 of these systems were sold for in use around the world. Some key features of the CM800 were the use of an industrial PC for the top end display and recording, the use of 3.5" magneto-optical (MO) disks as the recording medium, the use of a custom splashproof keypad for control and annotation, and the option of a fibre optic (FO) tow cable for intermediate depths. At the time these features were unique in a sidescan sonar. Our challenge was then to improve on the CM800 and at the same time to address the growing market for systems with a deeper capability.

The new CM2 system was introduced in 2002, superseding the CM800. The CM2 built on the success of the CM800 but improved on it in many respects.

The CM2’s new tow cable telemetry meant that both coax "soft" cables or very long twisted-pair cables could be used. A key point to note is that the CM2 is a true digital system, with the images being digitized in the towfish. Unlike sonars that rely on analogue towfish and analogue telemetry there is no loss of image quality in the tow cable.

The CM2’s top end electronics changed to the compact Sonar Transceiver Unit (STR) that links to a laptop via a USB cable. For a period an all-in-one clamshell unit (the C-Case) option was offered, replaced now by the optional C-Shell waterproof housing for the STR.

In the towfish, the basic configuration was carried over from the CM800 but improved in nearly every respect. The transducers were now protected by wider "wings". As well as providing protection these "wings" serve two other functions. The first is that they maintain the pitch stability of the towfish. The second is that they act as acoustic reflectors, primarily for the high frequency beams, cutting down the signal in the upper sidelobes by an average of 20dB. This significantly reduces any interference by surface echoes when working in shallow water.

The transducers retained our unique configuration that includes an additional pair of depressed short arrays that ensure good coverage directly below the towfish, and also act as an echo sounder to allow the towfish to measure its altitude automatically.

The CM2 towfish kept the stainless steel construction and the double O-ring sealing design that has ensured that no CM2 or CM800 towfish has ever leaked. The CM2 towfish also keeps the breakaway mechanism that, if an obstruction is hit, causes the towfish to flip and tow from the rear via a safety lanyard. This mechanism has proved so effective that very few towfish have been lost. A handle was added to the CM2 towfish to make one-man launch and retrieve even easier.

Our experience of the CM2’s reliability and our confidence in its design led us to increase the warranty period for most items from 12 months to 36 months.

Development has not stopped. In 2006 a new design of remote-control portable winch was introduced, replacing the SK172 type. This winch features an automatic overload clutch, “soft start” and a temperature alarm amongst other improvements.

A more recent development is the towfish wing depressor, taking advantage of the unique design of the CM2 towfish to put a high-aspect-ratio, efficient wing directly below the tow point. This wing is very effective in reducing the length of tow cable required to get to a particular depth, yet is light enough not to impede launch and recovery.

The range of compatible accessories has been extended to include large and small counting pulleys, a fixture for mounting the towfish on an overside pole, and an attachment for a USBL transponder.

On the software side, a new survey package MaxView was introduced in 2003. Since then MaxView has acquired a number of additional features, some of which are the direct result of customer feedback. It is notable that MaxView is available free-of-charge to any user of the survey data; the only function that requires the purchase of a software license is for the original acquisition of survey data.

The CM2 system is also directly compatible with most leading third-party survey packages.