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AIS - a major navigation advance

by on 5 May 2007
ComarSLR200 (1) Oceantalk
‘Greatest thing since sliced bread!’ That was the pronouncement of Sydney sailor Ian Potter of Sundancer II. He was talking about an AIS (Automatic Identification System) Receiver. Sundancer has had a chance to try out this brand new technology on their way across the Indian Ocean and up into the Med. over the last year.

With the danger of collision with a any fast moving ship always on the mind of cruising sailors and crusing motor yacht owners, this is a brilliant innovation that enables you, not only to see where the ships are, but to identify them as well. With a possible 12 minutes between horizon and collision, on any ocean, anywhere, it is not a small issue.

Ian had more to say: 'We were picking up ships at over 20 miles away and its so much easier to call them by name instead of 'vessel in approx position etc' . Going past the bottom on India we had up to 15 vessels displayed at one time.’

As Robin Kydd from Oceantalk the Australian distributor for the well proven Comar AIS system explains 'This technology is certain to give recreational boat owners an added dimension of safety and peace of mind through commercial shipping technology.

AIS transponders are now carried by all vessels over 300 tons. The AIS transponders transmits relevant vessel information: including Position, Speed, Heading, Call sign (MMSI number) Ships Name and Destination via a simple VHF signal.

This information can now be received by the AIS receiver on your own boat for display on the chart plotter screen. ( a system similar to aviation transponders that allow air traffic to be monitored and tracked on an air traffic controller’s screen.)

The AIS data is incredibly useful to any skipper. You can view an unknown vessel’s MMSI number and call sign: (to allow digital selective calls (DSC) to be made to that vessel.) Knowing the intended course and speed of an oncoming ship could assist you in plotting an alternate course. Keeping an eye on precisely how many ships are in the area, whether they are leaving port or entering. Even to record the Ships position and name in your log could be useful.

The most important advance in navigation, probably in the last five year. It adds to radar, chart plot, allow skippers to concentrate on the smaller boats that do not have AIS

Comar produce two main models, SLR200 Receiver only, and the CSB200 Transponder (Transmits as well as receives.) The units only require a marine style VHF Antenna. Recreational vessels are not legally enforced to carry either type but would be encouraged to fit the SLR200 Receiver in the very least.

The Comar SLR 200 AIS Receiver decodes and allows display of any AIS data received on Raymarine C and E Series displays. The SLR200 unit retails for less than AUS $1000 and is a worthwhile addition to any navigation system.

The Comar CSB 200 transponder is both a receiver and transmitter of AIS data. It gives recreational boats the ability to transmit their own AIS signal in order to recognize and be recognized by other AIS equipped vessels.

Introduced primarily as a vessel safety measure, all vessels over 300 tonnes will be required to fit an AIS transponder by the end of 2007. The safety benefits of AIS data means that many more, non-legislative vessels, are fitting both AIS receivers.

The introduction of affordable AIS receivers, such as the SLR-200 from Comar, enables users to see at a glance a visual display and detailed data about vessels in the area. This is especially useful at night, in fog, or in busy shipping lanes. The speed and accuracy of AIS information is paramount, with information updated every three seconds to six minutes, depending on the category of information, the speed and the rate of turn of the vessel.

The SLR-200 will receive and display the name of the vessel, call sign, type of vessel, destination, speed, course, heading, rate of turn, position, navigation status, vessel dimensions and MMSI number. With all this data, the user can ascertain and monitor vessel movements in the area, plot the progress, changes in heading and speed of nearby vessels, and, if required, call up the vessel.

Designed for use in the hostile marine environment, the SLR-200 is a robust, dual channel AIS receiver, incorporating a synthesised VHF receiver unit in its compact casing. Measuring just 140mm by 120mm by 50mm, it comes complete with trunnion mount, power cable, PC serial cable, NMEA cable and a combined installation/instruction manual.

The SLR-200 is quick and easy to install, requiring a 12/24vDC power source. It is connected to the PC via the serial port and to an external VHF aerial. For ports and harbour authorities, the SLR-200 is an affordable alternative to a high cost full Class ‘A’ unit, enabling them to monitor traffic within the VHF range, track vessels in the areas, and check on the legality of transit, and compliance with speed regulations

The data available from the SLR-200 provides an immediate, visual insight into the status and movements of other vessels in VHF range. AIS capability is now included as a standard feature on the majority of PC navigation software. Integrating AIS data onto the vessel’s electronic chart display instantly improves the safety levels on board, with the quick access to a MMSI (Marine Mobile Service Identity) can often help avoid a potential collision.

Class A AIS unit broadcasts the following information every two to 10 seconds while underway, and every three minutes while at anchor at a power level of 12.5 watts:

  • MMSI number - unique referenceable identification
  • Navigation status - not only are "at anchor" and "under way using engine" currently defined, but "not under command" is also currently defined. 
  • Rate of turn - right or left, 0 to 720 degrees per minute
  • Speed over ground - 1/10 knot resolution from 0 to 102 knots.
  • Position accuracy - differential GPS or other and an indication if RAIM processing is being used
  • Longitude - to 1/10000 minute and Latitude - to 1/10000 minute
  • Course over ground - relative to true north to 1/10th degree
  • True Heading - 0 to 359 degrees derived from gyro input
  • Time stamp - The universal time to nearest second that this information was generated


In addition, the Class A AIS unit broadcasts the following information every six minutes:

  • MMSI number - same unique identification used above, links the data above to described vessel
  • IMO number - unique referenceable identification (related to ship's construction)
  • Radio call sign - international call sign assigned to vessel, often used on voice radio
  • Name - Name of ship, 20 characters are provided
  • Type of ship/cargo - there is a table of possibilities that are available
  • Dimensions of ship - to nearest meter
  • Location on ship where reference point for position reports is located
  • Type of position fixing device - various options from differential GPS to undefined
  • Draught of ship - 1/10 meter to 25.5 meters [note "air-draught" is not provided]
  • Destination - 20 characters are provided
  • Estimated time of Arrival at destination - month, day, hour, and minute in UTC

Robin Kydd Managing Director of Ocean Talk: 'I recently brought a boat down from Phuket to Singapore, fitting with the Comar SLR200. With heavy shipping traffic, it really simplified the navigators task. Knowing what the commercial traffic was doing, with speed and bearing, we could easily see what boats were of no concern and that let us worry about other smaller ships. This is certainly a major advance for leisure boater.

As the region’s leading supplier of marine electronics for many years, we are thrilled to be able to off the proven Comar Systems. This is cutting edge technology, a world first, and a product ideally suited to the Australasian boating market. And as with all our products, we have the expertise, technical support and after sales service to do the system justice,' .

Find out more by calling Oceantalk on 02 9981 9500, fax 02 9981 9555, email or visit!Click_Here!same to comment on this article
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