Tag Archives: radar transponder

AIS and the radar transponder (II)

We talked the other day about the differences between radar transponders and AIS transponders, because we are often asked what are they when we explain the benefits of AIS. We found today a very interesting conversation in La Taberna del Puerto, the well-known association of boaters in Spain, about an accident that took place last year close from England, particularly a collision between a 7.5m long yacht and a ferry with destination Bilbao.

There is a detailed explanation, and a report from the British Authority about the probable malfunction of the radar transponders.

There are many reasons to explain why a Class B AIS transponder is far superior to a radar transponder. It is important to understand that, nevertheless, no electronics nowadays will be able to substitute a good captain on board.

AIS and the radar transponder (I)

When we explain the functionalities of an AIS class B Transponder, we are often asked if that is the same as a radar transponder. The answer is clearly no. A radar transponder is an emergency device included in the internationally proposed GMDSS measures for search and rescue at sea, i.e., a radar transponder is used at critical situations, to detect radar targets at emergencies. This system is also called SART (Search And rescue Radar Transponder)

It works by answering to a radar eco signal. That is why it is sometimes called “responder”. When activated, it starts transmitting signals as soon as it detects one from a radar. It is expected to be mandatory in Spain since 2009.

Therefore, essential differences between a radar transponder and AIS, are:

- SART does not work on a regular basis, but only under emergency situations.

- SART does not identify ships, only sends a signal that lets a radar know that there is somebody out there.

- Therefore, SART does not let you tracking a fleet, and identifying them; it is only able to show unidentifiable targets with no extra information.

AIS has nevertheless it’s own emergency standard, proposed by IMO here. The proposal is the AIS-SART, not to be confused with the radar transponder, since it actually means: AIS Search And Rescue Transmitter. But we will write about this in future posts.