Maritime Safety Information (MSI) which includes both weather information and navigational warnings is broadcast on VHF by the Coastguard Maritime Rescue Co-ordination Centres (MRCC) every three hours.
MSI is defined in the Safety of Life at Sea (SOLAS) Convention, Chapter IV as comprising “navigational and meteorological warnings, meteorological forecasts and other urgent safety related messages broadcast to ships”.
The Global Maritime Distress and Safety System (GMDSS) is the name given to the maritime communication system for all types of vessel to vessel and vessel to shore communication, including routine communications as well as emergency and distress messages.
Within the GMDSS there are two independent systems for broadcasting MSI, the International SafetyNET Service (a system using satellite communications) and the International NAVTEX Service (which is a medium frequency telex system). In addition to meeting its international obligations the UK also currently provides MSI using VHF and MF radiotelephony. Although an increasing number of recreational boaters are choosing to fit NAVTEX, many still rely on VHF for access to MSI whilst on the water.
The content of the VHF and NAVTEX broadcasts and the schedule to which they are issued is published in the MCA's MSI leaflet.
An announcement is made on CH 16 as an alert to the broadcast, detailing the channel that should be selected - this information is also published in the MSI leaflet.
The content of the broadcast that follows (Routine A, B or C) will vary depending on the time of day it is being transmitted.
The information that the UK is required by international convention to transmit is issued on 518kHz backed up by further useful information on 490kHz such as actual weather conditions as recorded by selected weather stations around the UK coast. Details can be found in the MCA MSI leaflet.
Navigational warnings (WZ) for NAVAREA1 and the UK Coast can also be obtained from the UKHO web-site. Many of these warnings are of a temporary nature, but others may remain in force for several weeks and may be superseded by Notices to Mariners.
Rig moves and pipe laying operations have been deemed to be sufficiently visible by sight, by radar and through local navigation warnings, therefore these will not be included with the VHF MSI broadcasts (NAVTEX remains unchanged).