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What is AIS?
AIS is short for Automatic Identification System, an anti collision system for shipping. The main component in an AIS system is a transponder that listens for broadcasts from other ships and regularly transmits details of the ship it is fitted to with information about it's position and performance. Ships receiving the transmissions can build up a 'picture' of where local vessels are located.
A typical example is
© MaritimeTraffic.com
There are several web sites that present uptodate AIS information and they are easily found on the internet.
Transponders are either Class A or B, where Class A is designed for commercial use and Class B for leisure use. Class A is mandatory on ships over 300 Ton. It is also possible to obtain receivers which only have the ability to monitor AIS transmissions.
Class A transponders have more powerful transmitters, and transmit more information about the vessel and it's behaviour. The transmitted information comprises two parts, static and dynamic data.
Static data includes details of the vessel and it's characteristics.
| Static Data | Class A | Class B | |
| MMSI Number | Yes | Yes | |
| Callsign | Yes | Yes | |
| Ships name | Yes | Yes | |
| Overall dimensions, ref for position | Yes | Yes | |
| IMO Number | Yes | No | |
| ETA | Yes | No | |
| Destination | Yes | No | |
| Max present static draught | Yes | No |
Dynamic data is primarily about how the vessel is behaving.
| Dynamic Data | Class A | Class B | |
| Position | Yes | Yes | |
| SOG/COG | Yes | Yes | |
| Heading | Yes | Yes | |
| ROT | Yes | No | |
| MMSI Number | Yes | Yes |
Note the MMSI is the Maritime Mobile Service Identity which is unique to a vessel.
Update rates are different for Class A and Class B Transponders and the transmission technologies are different.
Because it transmits in the VHF band the system is essentially limited to line of sight and reliability is governed primarily by installation factors such as cable connections, location of the VHF antenna and connection to other systems such as GPS (where the postion information comes from) rather than the transmission system. The chosen transmission system has plenty of spare capacity. A factor that needs to be considered is the operators/navigators familiarity with the installed system.
AIS is a very a great bonus to navigation and when used with existing navigation systems can usefully add additional information. For example conventionl radar cannot see over headlands whereas AIS can.
© True Heading SL
It is also worth remembering that only vessels fitted with AIS transponders can be seen, so if no AIS is fitted or the AIS is switched off the vessel will not be visible. This is why it is importanmt that any AIS system supports the navigation process and is not treated as a replacement for proper navigation.
Installing AIS - is it that simple?
An AIS Receiver is quite straight forward especially if you connect to a PC. The True Heading Receiver, for example comes with a USB port (as well as NMEA0183 port) to power it from a PC and is especially useful if you want to use it on board a leisure vessel and do your navigation on a portable PC. Using the NMEA0183 port needs external power but then you can feed the information to a chart plotter.
For the Transponders installation does require a fair degree of preparation since you need certain information available to program the device. The programming is done from a PC via a windows programme. Some of the static information can only be entered once so preparation and care is needed. Any installation needs to be safely and securely fitted and if in you are in any doubt about doing the installation then get a suitably qualified tradesperson to undertake the task. After all when you really need AIS to perform loose connections will not help your safety. AIS also has to work with other systems and there may be interactions between systems that you had not expected.
For both the Transponder and Receiver you will need a VHF antenna and this can be shared with your VHF radio when an antenna splitter is fitted. In the case of a Transponder you will also need a GPS antenna to connect to the GPS receiver in the Transponder. Knowing the position of the GPS antenna on the vessel is important particularly on larger vessels. This information is programmed into the Transponder and is crucial because it is used to determine where precisely the vessel is and the space around it.
AIS and legislation
Legislation continues to evolve and since 31st December 2004 certain sizes and types of commercial vessels are required to fit Class A transponders. The hurdle is being lowered and by 2014 all fishing vessels, within the European Union, over 15 mtrs in length will need AIS. AIS is also being adopted for yacht races and it is not too difficult to envisage a situation where leisure vessels over certain sizes will be required to carry AIS.
Some countries are looking at making the use of AIS more widelspread and in the US there are fines for sending out incorrect AIS data.
Do I need AIS?
Well I guess we would say yes!
Our waters are getting busier every year and anything which can make our use of the waterways safer for everyone has to be worthwhile. AIS is considered by many to be a significant development in navigation safety.
In leisure vessels an AIS receiver must be a major advantage to safety of life at sea, and since they readily work with PC's and are relatively cheap then they must rank alongside GPS and VHF radio even if you still use good old paper charts, dividers, parallel rule and soft pencils!
For any commercial vessel they are an essential part of the kit list by now. Compared to Radar and chart plotters and other technology they are relatively inexpensive and sending out and receiving the position and performance of vessels relative to yours is a major consideration for safer navigation.
AIS Technical
Autopilot
Magnetic Compass
NMEA
Satellite Compass
Weather Instrument
True Heading CTRX Carbon + Class B Transponder
RRP £822.05 (Ex Del and VAT)
True Heading Carbon Pro Class A Transponder
RRP £2,183.21 (Ex Del and VAT)
True Heading Carbon + AIS Receiver
RRP £292.19 (Ex Del and VAT)