Department for Transport

Navigational warnings

The United Kingdom Hydrographic Office (UKHO) acts on behalf of the United Kingdom Government as the NAVAREA I Co-ordinator and UK National Co-ordinator for Radio Navigational Warnings within the World-wide Navigational Warning Service.  As such the UKHO is the focal point for receipt and assessment of information on potential navigational hazards and issues any necessary Radio Navigational Warnings relevant to its area of responsibility.  The UKHO element of providing this service is funded by the UK Government through the Ministry of Defence.

Broadcast of warnings

The Maritime and Coastguard Agency (MCA) is responsible for broadcasting the warnings issued by the UKHO to vessels at sea.

NAVAREA I warnings

NAVAREA I warnings are broadcast via EGC SafetyNET within thirty minutes of receipt of original information or at the next scheduled broadcast time on Inmarsat's AOR-E satellite (0530 - 0600 or 1730 - 1800 UTC).  Those relevant for the appropriate service areas of the UK NAVTEX transmitters are also broadcast twice per day on NAVTEX.  Navigational warnings remain in force until cancelled and are broadcast for as long as the information is valid.  Warnings may no longer be broadcast after a period of six weeks if the details are readily available in Notices to Mariners.

UK coastal navigational warnings (WZs)

Warnings are broadcast by the appropriate NAVTEX station(s) (Cullercoats, Niton, Portpatrick, Malin Head or Ostende) at each routine transmission time, every four hours, or upon receipt for information of a VITAL nature.  They are also broadcast by radio telephony (RT-voice) on VHF and/or MF from selected MCA locations (utilising at least three aerials) during the routine broadcast schedule and at 12 hourly intervals thereafter.

All "in force" WZ and NAVAREA I warnings are also available on the UKHO website at:

MCA leaflet 'Maritime Safety Information' (MCA/064) provides the schedules for routine NAVTEX and RT broadcast times. A copy of this leaflet can be obtained from the MCA storage company, EC Group, on:

Tel:    0845 6032431
Fax:    01375 484556

Criteria for warnings

The UKHO follows joint International Maritime Organization and International Hydrographic Organization guidance in both the selection of information to be issued as warnings and in formatting the warning messages.  Subjects in the following list, which is not exhaustive, are considered suitable for broadcast as a WZ or NAVAREA warning:

  • casualties to lights, fog signals, buoys and other aids to navigation affecting main shipping lanes
  • the presence of dangerous wrecks in or near main shipping lanes and, if relevant, their marking
  • establishment of major new aids to navigation or significant changes to existing ones when such establishment or change, might be misleading to shipping;
  • the presence of large unwieldy tows in congested waters;
  • drifting hazards (including derelict ships, ice, mines, containers, other large items, etc);
  • areas where search and rescue (SAR) and anti pollution operations are being carried out (for avoidance of such areas);
  • the presence of newly discovered rocks, shoals, reefs and wrecks likely to constitute a danger to shipping, and, if relevant, their making;
  • unexpected alteration or suspension of established routes;
  • cable or pipe laying activities, the towing of large submerged objects for research or exploration purposes, the employment of manned or unmanned submersibles, or other underwater operations constituting potential dangers in or near shipping lanes;
  • the establishment of research or scientific instruments in or near shipping lanes;
  • the establishment of offshore structures in or near shipping lanes;
  • significant malfunctioning of radio-navigation services and shore-based maritime safety information radio or satellite services;
  • information concerning special operations which might affect the safety of shipping, sometimes over wide areas, e.g. naval exercises, missile firings, space missions, nuclear tests, ordnance dumping zones etc.  It is important that where the degree of hazard is known, this information is included in the relevant warning.  Whenever possible such warnings should be originated not less than five days in advance of the scheduled event and reference may be made to relevant national publications in the warning; acts of piracy and armed robbery against ships;
  • tsunamis and other natural phenomena such as abnormal changes to sea level;
  • World Health Organization (WHO) health advisory information; and
  • security related requirements.

To inform the UKHO about such hazards with a view to a navigational warning being issued, contact the UKHO Radio Navigational Warning Section on:

Tel: +44(0)1823 353448

Fax: +44(0)1823 322352


The UKHO will determine the type of warning needed, the text, the broadcast system(s) to be used and the period of time over which a message needs to be broadcast.

Charges for warnings

The MCA will raise an invoice against the "causer" of the hazard to contribute toward the cost of broadcasting any necessary warnings.  The fees currently charged for each transmission of a warning are 30p plus VAT per word for RT voice broadcasts by HM Coastguard Radio and 8p plus VAT per word for NAVTEX broadcasts.

When requesting a navigational warning the UKHO should be provided with sufficient contact details and (whenever possible) a purchase order number to assist both the MCA with issuing an invoice and the recipient of the invoice in identifying the originator of the message and so facilitating payment.


For details of the World-wide Navigational Warning Service and in particular the UK aspects of this service, including the NAVTEX and RT broadcasts, please refer to Admiralty List Radio Signals Volumes 3 & 5 and The Mariner’s Handbook NP100.