Automatic Identification System (AIS) Introduction
I have read this take me back to the AIS Receivers COMPARE section.
Selecting the right AIS device.
Before selecting an AIS unit it is important to know, the following
- What is AIS and what does it do?
- How I can best benefit from the technology?
What is AIS?
AIS was originally developed as a collision avoidance tool to enable commercial vessels to ‘see’ each other more clearly in all conditions and improve the helmsman’s information about his surrounding environment. It enables ships and coastal stations to accurately locate and identify one another. An AIS transceiver (often referred to as a transponder) uses VHF radio and GPS technology to communicate with other nearby ships.
Due to the great safety benefits offered by AIS, this technology was made compulsory throughout the world in 2002 for all passenger ferries and vessels over 300 gross tonnes. The range or coverage of the system is similar to a VHF radios. The system also has the advantage that VHF radio signals will travel around bends and over islands giving better coverage than RADAR or enhancing a RADAR picture when used together.
The AIS system is designed to transmit and receive information about a vessel. This information includes its identity, position, speed and course along with other relevant information. Vessels within AIS range can receive information transmitted by other vessels and display this information on a dedicated AIS display, a Chartplotter, or PC navigation software. Combined with a shore station, this system also offers port authorities and maritime safety bodies the ability to manage maritime traffic and reduce the hazards of marine navigation.
The AIS system uses 2 dedicated VHF frequencies. It is important to note the AIS system enables AIS messages to be transmitted by different vessels on both channels simultaneously. This is important to remember when selecting an AIS receiver. See the section “What t look out for when selecting an AIS receive only product.
AIS transponders both send and receive AIS messages so they can both see and can be seen by other vessels within VHF range. Both Class A and Class B transponders have integral GPS receivers and 2 TDMA VHF radio receivers and a radio transmitter.
AIS receivers only receive AIS messages so vessels can only see other vessels within VHF range, they CANNOT be seen by these vessels.
What type of AIS product is on the market?
There are 3 different categories of AIS unit on the market
Class ‘A’ AIS transponder.
These were the first devices introduced to meet the IMO specification for mandatory installation on all passenger vessels and commercial vessels over 300 GT’s. As determined by the IMO specification, the frequency AIS information is transmitted by a Class ‘A’ device is dependent on the speed and navigational status (anchored, turning etc.) of the vessel and the time of transmission. No further information on Class ‘A’ will be provided in this section as these products are specifically for the commercial market.
These were the first devices introduced to meet the IMO specification for mandatory installation on all passenger vessels and commercial vessels over 300 GT’s. As determined by the IMO specification, the frequency AIS information is transmitted by a Class ‘A’ device is dependent on the speed and navigational status (anchored, turning etc.) of the vessel and the time of transmission. No further information on Class ‘A’ will be provided in this section as these products are specifically for the commercial market.
Class ‘B’ AIS transponder.
Class ‘B’ transponders have been developed to provide safety and navigation benefits of AIS to smaller vessels with lower cost and simpler installation when compared to Class ‘A’. As determined by the IMO specification, the frequency AIS information is transmitted by a Class ‘B’ device is every 30 seconds for vessels moving faster than 2 knots and every 3 minutes for vessels at anchor or moving slower than 2 knots.
Class ‘B’ transponders have been developed to provide safety and navigation benefits of AIS to smaller vessels with lower cost and simpler installation when compared to Class ‘A’. As determined by the IMO specification, the frequency AIS information is transmitted by a Class ‘B’ device is every 30 seconds for vessels moving faster than 2 knots and every 3 minutes for vessels at anchor or moving slower than 2 knots.
AIS receivers.
A wide variety of receivers are available on the market today. Most are compatible with modern Chartplotters and PC navigation programs. Most are ‘black box’ devices. Some come integrated with a small dedicated AIS display.
A wide variety of receivers are available on the market today. Most are compatible with modern Chartplotters and PC navigation programs. Most are ‘black box’ devices. Some come integrated with a small dedicated AIS display.
Buying a Class ‘B’ transponder or buying an AIS receive only device?
The decision is actually quite simple. If you believe your safety is going to be enhanced by seeing other vessels, then by definition they are going to benefit by seeing you. This particularly applies if you are planning to do night passages, passages in bad weather or cruise in areas where there is a high volume of commercial and fast ferry activity. In these circumstances you should consider a Class ‘B’ transponder.
If the above does not apply to you and all you want to be able to do is to view other vessels around you, a “receive only” unit is probably the solution for you.
Class ‘B’ Transponders
A Class ‘B’ transponder is the solution for the leisure, light commercial and non-mandatory market as it offers all the advantages of AIS and can be easily installed and connected to most chart plotters or PC based navigation software. Class ‘B’ units are also built to and IMO specification and should be Type Approved.
Benefits of installing Class ‘B’ AIS transponder
- “See and be seen”.
A Class ‘B’ transponder continuously receives information form all Class A and Class B equipped vessels around you and displays this information on your standard chart plotter or PC. At the same time your Class B will transmit your position to all AIS equipped vessels automatically. - Safety at night and in poor weather conditions
The Class ‘B’ AIS is a vital navigation tool in poor visibility conditions. The information received from other AIS ‘targets’ provides the user with vital navigation information and the position transmission alerts other vessels to the users location. - Combined with radar, AIS gives you the best possible picture of your situation in all conditions
- Safety in high traffic / commercial shipping areas
- Position transmission to authorities / nearby vessels in case of emergency
- Best possible picture of a dynamic environment (moving vessels)
- Graphically view your position in relation to other vessels when connected to suitable display
- Ability to ‘see around the corner’
- Track vessels of interest such as friends/ colleagues “See and be seen”.
What else will I need to consider for my Class ‘B’ installation?
You will need to consider the following items dependent on your installation.
1. Power requirement to suite the unit specification.
2. A dedicated VHF antenna or a VHF splitter specifically designed and approved for use with AIS
3. A dedicated GPS antenna
4. NMEA Multiplexer
5. To use the Class ‘B’ AIS to transmit your position it should be programmed with your vessels MMSI number. If you don’t already have one (e.g., for a VHF DSC radio) it can easily be obtained from the local radio licensing authority.
What to look out for when selecting an AIS receive only product.
Single channel, dual channel or dual parallel channel receivers.
As this is a safety product, there are a couple of things to bear in mind.
1. To cope with the volume of traffic AIS messages are transmitted on 2 channels simultaneously by different vessels.
2. The same ship can also change channels according to the time slot it is allocated for its next transmission.
3. Vessels with Class ‘B’ are only transmitting every 30 seconds or 3 minutes if at anchor or moving at less than 2 knots.
The only way to receive all messages is with a dual parallel channel receiver. Single channel or dual channel multiplex receivers will only on average receive half the number of transmissions from other vessels so not giving you a true position of their current location.
Will I need a multiplexer?
Very often a Chartplotter only has one NMEA input and therefore you may need an NMEA multiplexer. Some AIS receivers are now supplied with a multiplexer integrated into the receiver. In other words NMEA in and out. Talk to your Chartplotter supplier for more information.
Very often a Chartplotter only has one NMEA input and therefore you may need an NMEA multiplexer. Some AIS receivers are now supplied with a multiplexer integrated into the receiver. In other words NMEA in and out. Talk to your Chartplotter supplier for more information.
How do I know if my Chartplotter is AIS compatible?
Check with your supplier. Most modern plotters are AIS compatible. You may need to upload the latest software.
Will I need a splitter?
If you don’t want to add another VHF antenna and want to use the existing VHF antenna as a feed for your AIS, you will need a splitter. Some AIS receivers are now supplied with a splitter integrated into the receiver.
If you don’t want to add another VHF antenna and want to use the existing VHF antenna as a feed for your AIS, you will need a splitter. Some AIS receivers are now supplied with a splitter integrated into the receiver.
Will I need a dedicated display?
If you are planning to display your AIS targets on a chart plotter or use PC Navigation software programs then it is probably not necessary to have a dedicated AIS display unless you are looking for a solution with built in redundancy.
What else will I need to consider for my ‘receive only’ installation?
This will depend on the device and how you are planning to display the AIS targets. However you will need to consider the following
1. Power
2. VHF antenna. (Or a VHF splitter. Discuss with your installer for a well tested splitter)
3. NMEA Multiplexer
Benefits of installing an AIS receiver
- “Be seen”.
An AIS receiver continuously receives information from all Class A and Class B equipped vessels around you and displays this information on your standard AIS compatible chart plotter or PC. - Safety at night and in poor weather conditions
An AIS is a vital navigation tool in poor visibility conditions. The information received from vessels transmitting AIS offers the user vital navigation information and an easy way to make radio contact with vessels you may not be sure have seen you. - Combined with radar, AIS gives you the best possible picture of your situation in all conditions
- Safety in high traffic / commercial shipping areas
- Best possible picture of a dynamic environment (moving vessels)
- Graphically view your position in relation to other vessels when connected to suitable display
- Ability to ‘see around the corner’
- Track vessels of interest such as friends/ colleagues “See and be seen”.
I have read this take me back to the AIS Receivers COMPARE section.
This section focuses on the AIS technology most applicable to the leisure marine market and is supplied courtesy of AIS COMAR systems ltd.
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