Radio Survey

The NAVTEX system provides the automatic dissemination of local Maritime Safety Information (MSI) by Narrow Band Direct Printing (NBDP) operating in the Forward Error Correction (FEC) broadcast mode (see Section 0 for more details on FEC operation). Depending on the geographical features of its area of responsibility (in main, the length of coastline), the NAVTEX system may be chosen by Administrations as an alternative to providing such information by the Inmarsat-C EGC service.

The system provides navigational safety information, weather warnings and forecasts relevant to vessels within specified coastal areas.

Range is generally within 300 – 400 n miles.

Due to its large length of coastline and the limited communications range of the NAVTEX frequencies, Australia has no plans to provide a NAVTEX service. Coastal MSI is disseminated by Inmarsat EGC. The NAVTEX system is presently used by countries in Asia, the Middle East, Europe and North America.

Broadcasts of local MSI by land stations operating in the NAVTEX service are made on the (MF) frequency of 518 kHz. A second NAVTEX (MF) frequency of 490 kHz is available for national language broadcast. The (HF) frequency of 4 209.5 kHz is also allocated for nation NAVTEX transmissions. There is also provision for transmissions on other nationally assigned frequencies for national transmissions, which also be in language other than English. Some of these are on 424 kHz (refer to ALRS for details).

To receive NAVTEX broadcasts, a ship must be equipped with a dedicated NAVTEX receiver tuned to 518 kHz. Once switched on and programmed, the receiver will provide fully automatic operation and broadcasts will not be missed even if the bridge watch keeper is busy with other duties. Messages are received in printed form on a paper roll, and on recent models, displayed electronically with local storage.

These ‘MSLS’ or ‘MOB’ devices and systems are intended for very short-range crew retrieval applications. The MSLS is designed to allow for self help from the vessel or organisation where there is a risk of crew falling overboard by sounding an alert from the onboard receiver.

They are not part of the GMDSS, but may use frequencies which can be detected by both GMDSS vessels and non-GMDSS vessels.

One example is a device transmitting on VHF Ch.70 using DSC, having an integral GNSS receiver, and transmits periodically, an automated Distress-priority alert and DSC message with the associated text ‘MAN OVERBOARD’. The DSC message contains the GNSS position and time, which will be displayed on the vessel’s VHF DSC receiver. The units may also be fitted with an alerting light flashing at not-less than 20 flashes/min. If fitted, the light shall be capable of operating at least 6 h, which is also the main battery operation requirement. It may also be capable of being water activated.

A number of devices used as Man Overboard Devices (Maritime Survivor Locating Systems/Devices) use AIS technology based on the burst transmissions defined in Annex 9 of Recommendation ITU-R M.1371. Early versions of these devices have the maritime identity of the format 970xxyyyy, but newer units starting from 2011, use the format 972xxyyyy, (see footnote 1 below the Table), which has been internationally agreed in Recommendation ITU-R M.585-6, Annex 2, Section 2.

The devices should be certified by a competent testing house that they are sufficiently compliant with the IEC 61097-14 for the purpose it is intended, or fully compliant with overseas standards, such as RTCM 11901.1 (June 2012). Additional overseas standards for these devices are under development.

Portable two way VHF radiotelephone equipment is used for communications between survival craft and rescue vessels. It may also be used for onboard communications on channels 15 and 17. Newer models automatically reduce the power to 1 W when these channels are selected. The equipment typically comprises a small hand-held transceiver with integral antenna.

The equipment is operated in the same fashion as any hand held (or ‘walkie-talkie’) type unit. Controls are provided for volume, squelch and channel operation. Transmission – reception is controlled by a ‘push-to- talk’ switch located on the side of the unit.

GMDSS vessels over 500 GRT are required to carry three portable survival craft VHF transceivers. Vessels of 300–500 GRT carry two. They are usually stored on or near the navigating bridge, for easy transport to survival craft. As the equipment uses re–chargeable batteries, the transceivers are stored in a ‘drop in’ type of battery charging cradle.

The effective radiated power should be a minimum of 0.25 W. Where the e ective radiated power exceeds 1 W, a power reduction switch to reduce the power to 1 W or less is required. When this equipment provides for on–board communications, the output power should not exceed 1 W on these frequencies.

Primary batteries should have a shelf life of at least 2 years, and if identified to be user–replaceable should be of a yellow or orange colour or marking.

Since 1 January 2010, AIS – Search and Rescue Transmitters can be carried in lieu of Search and Rescue Radar Transponders on vessels subject to the 1974 SOLAS Convention.

The AIS-SART is designed to transmit AIS messages that indicate the position, static and safety information of a unit in distress. An AIS-SART has an integral position source (e.g. a GPS receiver) and accordingly, AIS stations receiving the AIS-SART signal are able to display the range and bearing to the AIS-SART.

AIS-SARTs can only be detected by AIS installations. They cannot be interrogated, and transmit autonomously once activated. AIS-SARTs use the Self-organizing Time Division Multiple Access (SOTDMA) protocol in the similar way to a Class A mobile AIS station.

An AIS-SART is designed to be deployed in a similar way to a SART in that it is designed to operate from a survival craft at a height of 1 m above sea level. It may be fitted as an integral part of a survival craft, and can be manually activated or de-activated. Automatic activation may be provided. It is supplied with a buoyant lanyard of highly visible yellow/orange colour to secure it to the survival craft.

An AIS-SART is to be equipped with a means which is either visual or audible, or both visual and audible, to indicate correct operation locally and be provided with test facilities for all functionalities using specific test information. An indication will be provided to show that the AIS-SART has been activated, is undergoing test and has completed test. There will also be an indication of the position fixing system status when the AIS-SART is activated.

The pre-set broadcast messages of SART TEST or SART ACTIVE should be seen as text adjacent to an AIS-SART target symbol on AIS installations fitted on vessels or shore stations in VHF reception range of the unit in distress, and is to be clearly distinguished from an AIS installation (i.e. a ship, AIS AtoNs, etc). In ships fitted with an AIS MKD (Minimum Keyboard and Display), the text only will be seen, together with range and bearing.

Search and rescue radar Transponders (SARTs) are the main means in the GMDSS for locating ships in distress or their survival craft, and their carriage on board ships is mandatory. The SART is a small, battery powered, omni–directional radar receiver and transmitter. They may also be incorporated into a float–free satellite EPIRB. The batteries fitted to a SART allow operation in the standby condition for at least 96 h, plus a further 8 h whilst being interrogated.

A SART operates in the 9 GHz (3 cm or ‘X-band’) radar frequency band and, on receiving a signal from a ship or aircraft radar, transmits a series of response (homing) signals. The SART can be activated manually or automatically (in some cases) so that it will thereafter respond when interrogated. The method of using and activating SARTs varies over the type available, but instructions are marked on the sides of all SARTs.

These response signals will be seen on the ship or aircraft radar screen as a line of 12 dots (0.64 n miles apart) extending approximately 8 n miles outward from the SART’s position along its line of bearing. This unique radar signal is easily recognised and allows the rescue vessel or aircraft to locate the survival craft. As the SART becomes closer, another 12 dots are produced, also 0.64 n miles apart (see Section 11.1.4).

A SART will not respond to 3 GHz radar (also referred to as 10 cm or ‘S-band’) radar.

On activation the SART will provide a visible and/or audible indication of its correct operation. It will also provide an indication when it is being interrogated by radar signals from a searching ship or aircraft.

A SART should respond when interrogated by a shipborne X-band radar with a scanner height of 15 m within 8 n miles. A SART should also respond when interrogated by a compatible X-band radar fitted to an aircraft operating at a height of 3 000 feet at a distance of at least 30 n miles.