Since the dawn of modern marine technology several functional innovations has been developed to cater the tracking needs of marine vessels. One of the most important developments is the AIS.

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Automatic Identification System, AIS - The Best Navigation Aid to Boaters Since the GPS

One of the fastest and biggest growth areas in marine navigation is AIS. Having a AIS transmitter unit onboard, will turn your boat into a radio beacon continuously transmitting speed and course and your identity. Conversely having an AIS receiver allows you to track a ships, COG, SOG when in VHF range. This can be very important information for navigating in shipping lanes and channels.

What is AIS?

AIS stands for Automated Identity System. The identity is the transmitting vessels MMSI number, current speed and course which are just some of the information you can get. AIS has been developed to help prevent collisions between commercial shipping. AIS has been a legal requirement on ships over 300GT for a while. In US waters it is required by commercial ships over 65ft and tugs over 26ft and over 600 HP.

Vessels with the proper equipment can receive/send the AIS signal over a special VHF radio frequency. The signal includes COG, SOG, CPA, (CPA stands for closest point of approach), MMSI which can then be plotted on a standalone AIS unit or the existing navigation or radar displays. The display shows the AIS target as long triangle symbol depicting vessel and the same symbol is used for a large ship or small fishing vessel. The triangle points in the direction the target vessel is moving. This allows shipping to monitor traffic always knowing what is happening around them at all times.

What are the Benefits of AIS to the recreational boater

Avoiding other vessels on the water, and it is especially in our best interests to avoid the big guys whether in a shipping channel or not. Large ships have restricted maneuverability and stopping range. Having discussed AIS with maritime industry workers including ship Captains and Pilots, I can tell you they really like the system.

Here are three reasons for AIS. One, you are in poor visibility, and are in a channel and suddenly the weather comes in rain, & winds. Now the ships that were once easily seen on deck are now invisible. Two, you are out on the wide ocean when a ship appears on the horizon. The watch is not looking and you have no wind and cannot start the engine. This is a true scenario. In this case your AIS signal would be picked up by the ships radar. The signal would sound an alarm on the bridge. Third, AIS Allows you to see around bends. Imagine a channel where you are coming up to a bend and there is a ship coming your way. You cannot see around the bend due to the raised shoreline, but you would be able to pick up the AIS signal on your chartplotter.

The Marine Accident Investigation Branch, MAIB has a report of a mid channel collision between a commercial Ferry and a small sailing vessel which resulted in the sailboat sinking and loss of life. The reports conclusion showed the sailing vessel did not appear on radar and because of the height of the bridge the sailboat was not seen by eye. The recommendation was for better radar reflectors so the sailboat could be seen on the ferries radar and or the use of AIS.

Types of AIS

There are two types of AIS class A or B. Class A is for Commercial shipping and transmits via 2 channels and typically is fully integrated into the ships navigation systems. Class B is for smaller vessels. You can choose to receive only or receive and transmit.

The Class B is nearly identical to the Class A, except the Class B: Has a reporting rate less than a Class A (e.g. every 30 sec. when under 14 knots, as opposed to every 10 sec. for Class A) Class B also does not transmit the vessels IMO number or call sign.

AIS signals are sent out over two VHF channels alternating between the two. Some receiver will pick up both channels and some are single. Single channels miss some information and less often.

Note; in the US the FCC has not yet sanctioned calls B transmitters but is coming soon, probably in the New Year 2008.

AIS and the necessary equipment

To get this signal and make use of it, you will need an AIS engine, a VHF antenna, a GPS signal, power and a display. You can use your existing VHF antenna but will loose some signal strength so it is best to get a dedicated antenna for AIS.

The AIS engine translates the AIS signal before it goes to the display. There are many AIS engines available on the market. Equipment that can show the AIS signal includes, any PC and Mac based navigation system. Most of all chartplotters later models from most manufacturers. These include, Garmin, Furuno, Si-Tex, Standard Horizon, Northstar, Raymarine, and many more. Standalone AIS displays are also available.

You can add a compass if you want to send your rate of turn, which can let another vessel project where you will end up after your maneuver.

You will need to register your MMSI number into the unit so it can be part of your signal. Someone receiving the signal either another vessel or a Coast Guard shore station VTS can see your signal and be able to call you by name and call sign.

How much will this Cost

AIS is not new but it is new to the recreational boater. We are in the 3rd generation of AIS and costs are now under 1,000. This makes AIS affordable for the cruiser. For example take a Furuno class A unit the FA150 which costs $4,000-4500. Compare this to the Furuno AIS receiver FA30 for under $740.

Class A or Class B

My discussions with the Pilots concluded that while they like the system and believe it should be on many recreational vessels, they worry about too many signals in crowded channels. They would have to deal with lots of targets on their plotters which could be confusing. They generally agree that they would filter out much of the class B traffic in crowded shipping lanes but turn it on in open water. So pay attention it's your responsibility.

Due to the Difference between Class A and Class B transmission rates, it would be useless for fast moving craft like high speed ferries. You will get a ping only twice a minute. At 20 knots the high speed ferry has moved quite a distance and in restricted visibility this could be too late. In this case Class A is for you.

For more on this article and its recommendations, lots of resources and diagrams see

http://myboatsgear.com/newsletter/2007120b.asp

Mike Hobson is Editor for http://www.myboatsgear.com

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