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.
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.