Wikipedia describes AIS as follows
The Automatic Identification System (AIS) is an automatic tracking system used on ships and by vessel traffic services (VTS) for identifying and locating vessels by electronically exchanging data with other nearby ships and AIS Base stations. AIS information supplements marine radar, which continues to be the primary method of collision avoidance for water transport.
Information provided by AIS equipment, such as unique identification, position, course, and speed, can be displayed on a screen. . AIS is intended to assist a vessel's watch standing officers and allow maritime authorities to track and monitor vessel movements.
If you are sailing mainly in sheltered waters, away from commercial traffic, then you really don't need it - but if you sail in areas where there are many ships, then in fog or at night, it can be a life saver. A couple of times recently we were sailing in the Gibraltar Strait area and unexpectedly ran into thick fog. Whilst our Radar and MARPA (mini-automatic radar plotting aid) showed clearly the tracks of ships around us, and those on possible collision course with us, there was no easy means of identifying them by name thus making VHF contact difficult and unreliable.
Having been badly scared by a couple of close encounters both in fog and at night, we decided to fit AIS (Automatic Identification System).
The web sites below show active AIS all round the world and you can see exactly how it works, and how easy it is to get in touch with vessels who could cause a threat in difficult conditions.
What I have gained by installing a AIS transponder is this:
Sailing or motoring, particularly at night or in fog, I can see the course and track of all vessels over 500 tons in my vicinity. If I am concerned about the proximity of one, I can 'highlight' them, and the system will tell me their course, speed and if we are on possible collision courses and how long to that happening.
If I then decide that I should communicate with the other vessel I have their ships name, call-sign displayed so there can be no ambiguity as to whom I am calling on VHF.
Equally important is the other vessel can 'see me' on his screen and identify a sailing boat. The other vessel can contact me, as my call sign and name are displayed. If I call then the officer of the watch knows which, of perhaps several small boats displayed on his system, I am.
There are two options for small vessels, assuming you will not be fitting a 'Class A' commercial AIS system, which is serious money and whilst being far more powerful = longer range = are not really for pleasure craft.
The first option is a transceiver/transponder which receives the AIS signal from other AIS stations and transmits your AIS identification back to other craft. This has the advantage that when you call up a 'big ship' they will see your vessels name, course speed etc on their own AIS screen and know which, of perhaps several small craft showing on their radar/AIS, they are talking to. The cost of this system 'class B transceiver is around £800 with the required VHF antenna.
A couple of examples below:Simrad AI50 class B
Yachting ST/STEEL MASTHEAD ANTENNA AIS
I purchased the Simrad A150 as it has a colour screen, I find the display pleasing, and because I wanted it in front of the helm so it needed to be waterproof. Not only will it display the call sign and name of the other vessels, it will provide the course and speed, lat & long and if it is on a collision course with you and when that will happen. You can also put in guard zones and closest permitted passing distance. It has a world map built in showing all the coastlines.
The alternative are the 'passive' types of AIS which of course are much cheaper but do not let the 'ship' you are calling know which, of all the pleasure boats it has on it's radar, is you,,,, It comes in various forms with either their own display or via your laptop in the boat. You will still need a dedicated GPS antenna and a VHF antenna which are not included in the price shown below.
Nasa AIS Radar
requires GPS antenna or splitter
Clipper AIS Enginee 3Nasa
AIS Engine 3
(requires a laptop)
XM Yachting ST/STEEL MASTHEAD ANTENNA AIS
To call the NASA a radar is hyperbole - Radar is something which enables you to be out in zero visibility with some degree of safety. It will also show vessels of less than 500 tons, buoys, land, objects in the sea. AIS is only required on vessels of over 500 tons and bits of land or other hard stuff will not show up. I get the impression with these two NASA / AIS you need a GPS feed and an a VHF antenna. (With the Simrad and Icom they supply the GPS antenna but not the VHF antenna.
(Technical details of all of the above are at the bottom of this page.)
I am fairly certain that if you are in the market for a new chart plotter or new radar, it will come with a built in AIS transponder, still requiring GPS and VHF antenna as extras but none the less is of course the perfect solution. Whilst most radar systems have had MARPA (mini-automatic radar plotting aid) for years, I suspect most of this and the next generation will have AIS built in as standard.
I installed the Simrad A150 myself, which took most of the day. the hardest part being the cable run and finding a nice bit teak to mount the display in front of the wheel.
Normally I turn the chart plotter off, once we are out at sea, and tend to rely on the GPS display and in poor visibility on the radar. Now I will have the important, additional information, from the AIS in front of me.
For almost all the Transponder type AIS you need to install a GPS antenna which they supply with the receiver as well as a VHF antenna or splitter.
I have a pole with a T on the top, mounted on the stern of. On it is the Navtext antenna, the Raytheon system GPS antenna and the stern light - (the lower one being masked by the dinghy when it is on the davits.) To the above I added the GPS antenna supplied by Simrad and the XM yachting antenna that was reccomended for the SIMRAD AIS system.
The GPS antenna on the left came with the Simrad and the VHF antenna is a XM Yachting ST/STEEL MASTHEAD ANTENNA AIS which did not come with the kit..
Displayed above the helm is the Simrad AIS, the GPS and the Radar/Chart plotter not to mention the compass which is almost certainly driven crazy by all the electronics around it but none the less useful. I have yet to have a season with the new Simrad AIS but I am optimistic it will be invaluable and make contacting large vessels much easier.
All the above is just my opinion - if you think I am wrong or want to add to the article please email me - here
scroll down for technical details of AIS mentioned above
For my sailing books and French canal guides please go to
The prices mentioned are circa 2015 and are for comparison.
Clipper AIS Engine 3Nasa
AIS Engine 3
French Canal Routes to the Mediterranean
Gentle Sailing Route to the Mediterranean
CRUISING SOUTHERN SPAIN AND THE COSTA DEL SOL
Gentle Mediterranean Routes to the Islands
Caribbean Islands Cruising Guides
Living Aboard Around the World
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