Friday, November 18, 2011

AIS Receivers on VHFs?


Chuck Husick: Techno-Talk, May 2005 from BoatUS Magazine - Updated July 2009

AIS Receivers on VHFs?

The article "Big Brother's Little Box" (March 2004 BoatUS Magazine) describes the Class A Automatic Identification System (AIS) now required on all SOLAS vessels, numerous other ships and almost all tugboats. However, while the information contained in the AIS signal broadcast from these vessels can be of immense value to everyone, the cost of a full AIS unit can exceed thousands of dollars, too high for many recreational boaters. Even the Class B AIS, recently approved for sale in the US can cost $600 to more than $1200.

It is possible to gain use of the wealth of information contained in the AIS signals with use of an AIS receiver, without the added and substantial cost of getting in the loop by adding a transmitter. Receivers are available at prices ranging from less than $200 to $500. However, we have long believed that there is a wonderful opportunity for the manufacturer’s of marine VHF/DSC radios to provide virtually all the advantages of AIS to recreational vessels at a price only a couple of hundred dollars above the cost of a conventional radio. This idea has been discussed with each of the major VHF radio manufacturers and has recently been addressed by Garmin with the introduction of their VHF 300 AIS. A European manufacturer of VHF/DSC radios has stated their intent to introduce an AIS capable radio later this year. Another manufacturer's VHF/DSC radio was equipped with an internal AIS capability by a third party, however the maker of the radio disclaims all interest in what was accomplished.

The introduction of the Garmin 300 AIS is, in our opinion a step in the right direction for boats that navigate in high traffic areas. With a suggested retail price of $1,000 it leaves unaddressed the market for less costly VHF/DSC/AIS radios, a market we are confident will be addressed by other manufacturers in the coming year. We think BoatUS members and all other recreational mariners should encourage radio manufacturers to build the AIS receiver into their Class D VHF/DSC radios, (this makes sense for a number of reasons. The radio is already connected to an antenna, its receiver “front end” can handle the AIS information on channel 87B or 88B with an added circuit used to detect the AIS bit stream). The needed GPS information is already present in the radio where it is used to make the DSC function operational. The additional circuitry and the processor needed to construct the NMEA 0183 AIS sentence will not be very expensive and can share the power supply circuit already in the radio. The radio can deal with the AIS information as a "blind box"feeding the information to the chart plotter/radar and/or it can use its LCD screen to display the AIS data it receives.

The built-in AIS could also display data on the radio’s LCD screen. Display screens on VHF radios are getting bigger and transitioning to color, however most of the time the information they show is static, just the channel number in use. The screen could provide a basic AIS display showing the relative bearing and distance of AIS-equipped vessels within a selected range, perhaps 6 or 12 miles. As in a full capability AIS, the system could predict and display the distance and time of closest approach to the other vessels.

There are times when being able to communicate directly with the bridge of a nearby vessel is very helpful. Today, except for the few instances when we can see the name of the other vessel we are limited to calling "the blue hull tanker passing green 7". With the system we envisage, a "click" on the AIS target of interest would display the information about the target of interest, and automatically load the target’s MMSI into the radio’s call list. You would select a working channel, punch the DSC enter button and immediately gain the attention of the bridge watch on the other vessel.

Using this listen-only approach means that while the AIS equipped vessels won’t hear from you, you will know all about them. We believe that just listening (and not talking) is a reasonable way to make use of the system since large ships and tugs are primarily interested in other similar vessels and are unlikely to do much maneuvering to avoid a close call with a recreational vessel. Regardless of the Rules of The Road, we are the ones who will have to maneuver to avoid a collision. However when communication with other nearby vessels is desirable you will know what vessel to hail.

By cooperating with other traffic we minimize everyone’s anxiety. AIS does for marine navigation what the latest radar transponder and collision avoidance equipment does for aviation, reduce the collision risk "pucker factor" to close to zero.

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