Chart Correction and Notices to Mariners

Keeping charts up to date is a legal requirement for commercial vessels and a matter of safety for all mariners. The primary mechanism for chart correction is the weekly edition of Admiralty Notices to Mariners (NMs), published by the UKHO. Each weekly edition contains corrections, new editions, and important navigational warnings.

Notices are categorised into several types. Permanent notices describe lasting changes such as new buoys, altered lights, or changed depths. Temporary (T) notices cover changes that will last for a limited time, such as a temporary light on a construction site. Preliminary (P) notices give advance warning of expected changes. T&P notices are marked on charts in pencil so they can be erased when cancelled.

The chart correction procedure involves: (1) recording the NM number and date on the chart's correction log (bottom left corner), (2) applying the correction in waterproof violet ink for permanent changes or pencil for T&P notices, and (3) striking through any superseded information neatly. The correction log allows anyone to verify which NMs have been applied.

For leisure sailors, chart correction packs (Admiralty Small Craft Editions) simplify the process. Electronic chart updates can be downloaded from chart providers. Regardless of the method, navigating with an out-of-date chart is a serious safety risk — hazards, buoyage, and depths can all change.