AIS to improve search and rescue

Work currently underway by the Radio Technical Commission for Maritime Services (RTCM) will create two new life saving electronic devices, a replacement for the search and rescue transmitter (SART) now carried in lifeboats on Safety of Life at Sea (SOLAS) and other vessels, including yachts, and a new type of 406-MHz EPIRB that will transmit an AIS signal. The new AIS SART (allowed on SOLAS vessels starting Jan. 1, 2010) will derive its position from an integral GNSS (GPS) receiver and will broadcast its position eight times each minute, updating its position once each minute. Final approval for this new device is still underway at the International Electrotechnical Commission (IEC).

The present SART is a transponder, a combination of a receiver and transmitter that responds to the signal emitted by a marine X-band radar by emitting a signal that appears on the searching vessel’s radar screen as a unique series of “blips.” The signal from the new AIS SART does not depend on illumination of the SART by the searching vessel’s radar, but will appear on the AIS capable radar or chartplotter of any vessel in range, normally beyond five miles for a surface ship.

The second improved device now under consideration is an EPIRB that will, in addition to the 406-MHz satellite signal and the 121.5-MHz homing signal, emit an automatic identification signal (AIS) that, like the signal from the new SART, can be detected by any ship or vessel equipped with an AIS receiver or AIS transponder.

The immense value of an AIS capable EPIRB can be appreciated when you consider the following scenario. An EPIRB signal is received by a rescue coordination center. Among other actions the RCC checks for the presence of Amver (Automated Mutual-Assistance Vessel Rescue System) reporting ships in the vicinity of the EPIRB. An alerted ship will proceed to the reported location of the EPIRB to search for the vessel or person in distress.

While distress signaling has employed the latest in satellite and GPS technology, the ship’s search will be conducted visually, entirely without electronic aid (with the possible exception of the ship’s radar). The ship does not carry radio receivers capable of receiving or homing on either the 406-MHz or the 121.5-MHz signals being emitted by the EPIRB. The addition of the AIS signal will make the location of the EPIRB visible on the ship’s radar/chartplotter.

Effective reception range for both the new AIS SART and the likely AIS enhanced EPIRB will depend on the VHF radio propagation, including the height of the receiving antenna above the sea, the elevation of the transmitting antenna in the EPIRB or SART and the sea-state.

Chuck Husick

By Ocean Navigator