Understanding Notices to Mariners: Importance in Safe Maritime Navigation

A nautical chart is only as safe as its most recent correction. The seabed shifts, wrecks appear, buoys move, and depths change. A chart printed last year may already show a hazard in the wrong place or miss a new one entirely. Notices to Mariners exist to close that gap, and keeping charts corrected with them is both safe practice and a carriage requirement that port state control will check.

What Are Notices to Mariners?

Notices to Mariners (NtM) are official corrections to nautical charts and publications, issued regularly by hydrographic offices. A Notice carries only information that affects safety at sea: a new wreck, a relocated buoy, a changed depth, a discontinued light, or a new restricted area.

Over 60 countries that produce nautical charts also issue their own Notices. The two most widely used services are:

• ADMIRALTY Notices to Mariners, published weekly by the UK Hydrographic Office (UKHO) for its worldwide chart series.
• U.S. Notice to Mariners, published weekly by the National Geospatial-Intelligence Agency (NGA) and the U.S. Coast Guard.

The rule is simple: mariners must keep charts corrected up to date with the relevant Notices until a new edition is published. A Notice only applies to an edition currently in force. Once an edition is cancelled and replaced, earlier Notices no longer apply, and corrections begin fresh against the new chart.

What a Notice to Mariners Contains

A weekly ADMIRALTY Notices to Mariners booklet follows a fixed structure, which makes finding the right correction faster. The booklet opens with explanatory notes, then a geographical index, then the index of charts affected that matches each chart number to the Notices correcting it, followed by the individual corrections themselves. Separate sections cover navigational warnings and amendments to publications such as Sailing Directions and the List of Lights.

Notices come in three types:

• Permanent Notice: corrects a chart until its next edition.
• Temporary (T) Notice: covers a short-lived change, such as a buoy off station, and is applied in pencil so it can be removed.
• Preliminary (P) Notice: gives warning of planned work, such as dredging or construction, before full details are confirmed.

How to Correct a Chart Using Notices to Mariners

Correcting a paper chart follows a consistent sequence. The steps below apply whether you maintain a single chart or a full outfit. Work carefully, because a vessel's safety depends on the accuracy of each correction.

Step 1: Gather Your Materials

Collect the weekly Notices to Mariners, the affected charts, violet waterproof chart-correction ink, a pencil for temporary corrections, and a straightedge. Approved chart correction and plotting tools keep the work precise and legible.

Step 2: Check the Index of Charts Affected

Turn to the index of charts affected at the front of the weekly Notice. Locate each chart you hold by its number. Listed beside it are all the Notices that apply to that chart for the week.

Step 3: Apply Each Correction in Sequence

Work through the listed Notices in order. Use violet ink for permanent corrections and pencil for temporary (T) ones. Where a change is too complex to draw by hand, the Notice supplies a printed "block," an adhesive patch that you cut out and paste over the affected area.

Step 4: Record the Notice Number

After each correction, write the Notice number in the bottom margin of the chart. Recording it there creates the on-chart record that shows the chart is corrected to date.

Step 5: Log and Verify

Enter every applied Notice in the vessel's chart correction log. Before a voyage, confirm that each chart for the intended passage is corrected to the latest available Notice. The log is the audit trail a port state control officer examines.

Why Keeping Charts Corrected Matters

Corrected charts are the difference between trusting outdated data and verifying it at the moment accuracy matters most. A chart showing 12 meters where shoaling has reduced depth to 6 meters can ground a vessel. A chart still showing an extinguished light sends a bridge team chasing a reference that no longer exists.

Corrected charts are also a legal carriage requirement. SOLAS Chapter V obligates vessels to carry adequate and up-to-date charts for the intended voyage, and a vessel with uncorrected charts can be detained during a port state control inspection. Electronic chart services such as AVCS apply weekly updates digitally, but the navigator still confirms, applies, and verifies them on ECDIS.

Keep Your Charts Current, Sail With Confidence

Notices to Mariners turn a static chart into a living record of the sea as it is right now. Applying them is one of the clearest expressions of professional diligence on any bridge. For corrected nautical charts, ADMIRALTY and NGA publications, and chart maintenance resources, contact American Nautical Services at +1 (954) 522-3321 or sales@amnautical.com.

Frequently Asked Questions

Q. What is the meaning of Notice to Mariners?

A Notice to Mariners (NtM) is an official correction issued by a hydrographic office to update nautical charts and publications with safety-critical information, such as changes to depths, wrecks, aids to navigation, and restricted areas.

Q. How often are Notices to Mariners issued?

ADMIRALTY Notices to Mariners are published weekly by the UK Hydrographic Office. The U.S. Notice to Mariners is also published weekly by the NGA and U.S. Coast Guard. Over 60 countries issue their own national Notices.

Q. What is the difference between a permanent, temporary, and preliminary Notice?

A permanent Notice corrects a chart until its next edition. A temporary (T) Notice covers a short-lived change and is applied in pencil. A preliminary (P) Notice gives advance warning of planned work before full details are confirmed.

Q. Are vessels required to correct their charts?

Yes. SOLAS Chapter V requires vessels to carry adequate and up-to-date charts for the intended voyage. A vessel with uncorrected charts can be detained during port state control inspection.

Q. How do you correct a paper chart using NtM?

Identify affected charts using the index at the front of the weekly Notice, apply each listed correction in sequence using violet ink or pencil, paste any block corrections, then record each Notice number on the chart and in the correction log.

Q. Do electronic charts still need Notices to Mariners?

Yes. ENC services such as AVCS deliver weekly updates digitally, which the system applies once confirmed. The navigator remains responsible for receiving, applying, and verifying updates and for ensuring no charts have lapsed.