You are the officer of the watch. It's a dark night. You are tracking a dozen or more targets on your marine radar system. One of the blips on the radar screen seems to be turning to its right. You pick up the VHF microphone and check to see that it is set for the correct hailing channel.
"Vessel on my starboard bow, this is MV Eversail. It appears you may be making a turn to starboard. Do you intend to cross my bow? Over."
"Eversail, this is MV Seafarer. Are you the ship in the inbound lane near buoy 23? Over."
"Seafarer, this is Eversail. That's a negative. I am at the junction buoy near Deadman's Reef. Over."
"This is Seafarer. Roger out."
Silence...
"Eversail, this is MV Oceanbreeze. I think I am the vessel off your starboard bow. I am outbound in the auxiliary channel from the tanker berth. I am slowing to disembark the pilot. Over."
"Oceanbreeze, this is Eversail. I have you on my radar. You are not the ship I was calling. Over."
Silence...
"Vessel five miles off my starboard bow, this is MV Eversail in the outbound channel passing Deadman's Reef Junction Buoy. What are your intentions? Over."
"Eversail, this is MV John Brown. I think I am the vessel off your starboard bow. Over."
"John Brown, this is MV Seafarer. I believe I am astern of you. Are you the ship that's just passing Buoy 23? Over."
And so forth...
Radio exchanges like these are a common occurrence on ships at sea, especially when transiting a busy shipping lane. All ocean-going ships are required to carry collision-avoidance marine radar systems that automatically plot course and speed vectors for targets being tracked. The weak link, however, is the inability to identify any given radar target on the screen when multiple contacts are being tracked. This is especially true at night or in reduced visibility when it is impossible to verify a ship's identity visually.
Which blip belongs to which ship? This is one of the most confusing areas of sailing navigation. And this inevitable confusion is a contributing factor in many collisions and near-collisions at sea.
A new technology called Automatic Identification Systems (AIS) helps to resolve this difficulty by providing a means for ships to exchange ID, position, course, speed and other vital data with all nearby ships and shore stations through a standardized data transponder.
The AIS concept derives from the pioneering work of Swedish inventor Hakan Lans, who developed a scheme called Self-Organizing Time Division Multiple Access (STDMA). This scheme permits a large number of transmitters to send data bursts over a single narrowband radio channel by synchronizing their data transmissions to a precise timing standard. In the case of AIS, the timing signal derives from GPS.
The Safety of Life at Sea (SOLAS) treaty requires ships over 300 gross tons, that are on international voyages, to be equipped with an approved AIS transponder. In addition to ship-to-ship reporting, AIS can be used for ship-to-shore and shore-to-ship transmissions. A number of nations in the European Union are constructing inland AIS-based infrastructure to monitor movements of vessels on rivers and canals. Many coastal nations also are establishing automated AIS networks of shore stations for surveillance of ships sailing through their coastal waters.
A new standard called AIS-B recently has been developed for voluntary installation on smaller vessels that are not subject to the SOLAS carriage requirements. AIS-B is designed for private fishing boats, pleasure boats and the like.
The new generation of marine radar systems frequently has built-in capability to overlay AIS data on the radar picture. Thus, the vessel's ID, course, speed and other data are shown as a tag or in a separate window for each AIS target.
If you're interested in learning more about AIS, you can find a great deal of useful information at the U.S. Coast Guard Navigation Center. www.navcen.uscg.gov/enav/AIS/default.htm Another good resource is Saab Transponder Tech, the company that did much of the pioneering work in AIS technology in the late 1990s. In 2008 Saab was one of the first companies to introduce an approved AIS-B transponder for smaller craft. www.saabgroup.com/en/AboutSaab/Organisation/SaabTransponderTech/News.htm
"Vessel on my starboard bow, this is MV Eversail. It appears you may be making a turn to starboard. Do you intend to cross my bow? Over."
"Eversail, this is MV Seafarer. Are you the ship in the inbound lane near buoy 23? Over."
"Seafarer, this is Eversail. That's a negative. I am at the junction buoy near Deadman's Reef. Over."
"This is Seafarer. Roger out."
Silence...
"Eversail, this is MV Oceanbreeze. I think I am the vessel off your starboard bow. I am outbound in the auxiliary channel from the tanker berth. I am slowing to disembark the pilot. Over."
"Oceanbreeze, this is Eversail. I have you on my radar. You are not the ship I was calling. Over."
Silence...
"Vessel five miles off my starboard bow, this is MV Eversail in the outbound channel passing Deadman's Reef Junction Buoy. What are your intentions? Over."
"Eversail, this is MV John Brown. I think I am the vessel off your starboard bow. Over."
"John Brown, this is MV Seafarer. I believe I am astern of you. Are you the ship that's just passing Buoy 23? Over."
And so forth...
Radio exchanges like these are a common occurrence on ships at sea, especially when transiting a busy shipping lane. All ocean-going ships are required to carry collision-avoidance marine radar systems that automatically plot course and speed vectors for targets being tracked. The weak link, however, is the inability to identify any given radar target on the screen when multiple contacts are being tracked. This is especially true at night or in reduced visibility when it is impossible to verify a ship's identity visually.
Which blip belongs to which ship? This is one of the most confusing areas of sailing navigation. And this inevitable confusion is a contributing factor in many collisions and near-collisions at sea.
A new technology called Automatic Identification Systems (AIS) helps to resolve this difficulty by providing a means for ships to exchange ID, position, course, speed and other vital data with all nearby ships and shore stations through a standardized data transponder.
The AIS concept derives from the pioneering work of Swedish inventor Hakan Lans, who developed a scheme called Self-Organizing Time Division Multiple Access (STDMA). This scheme permits a large number of transmitters to send data bursts over a single narrowband radio channel by synchronizing their data transmissions to a precise timing standard. In the case of AIS, the timing signal derives from GPS.
The Safety of Life at Sea (SOLAS) treaty requires ships over 300 gross tons, that are on international voyages, to be equipped with an approved AIS transponder. In addition to ship-to-ship reporting, AIS can be used for ship-to-shore and shore-to-ship transmissions. A number of nations in the European Union are constructing inland AIS-based infrastructure to monitor movements of vessels on rivers and canals. Many coastal nations also are establishing automated AIS networks of shore stations for surveillance of ships sailing through their coastal waters.
A new standard called AIS-B recently has been developed for voluntary installation on smaller vessels that are not subject to the SOLAS carriage requirements. AIS-B is designed for private fishing boats, pleasure boats and the like.
The new generation of marine radar systems frequently has built-in capability to overlay AIS data on the radar picture. Thus, the vessel's ID, course, speed and other data are shown as a tag or in a separate window for each AIS target.
If you're interested in learning more about AIS, you can find a great deal of useful information at the U.S. Coast Guard Navigation Center. www.navcen.uscg.gov/enav/AIS/default.htm Another good resource is Saab Transponder Tech, the company that did much of the pioneering work in AIS technology in the late 1990s. In 2008 Saab was one of the first companies to introduce an approved AIS-B transponder for smaller craft. www.saabgroup.com/en/AboutSaab/Organisation/SaabTransponderTech/News.htm
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