New Zealand's Hydrographic Authority has published Edition 21 of the Notices to Mariners, delivering official chart and navigation updates for local waters. The changes in this edition are modest in scale, but their importance to safe navigation should not be underestimated.
Two areas in particular draw attention. At the Manukau Harbour Entrance, six subsurface scientific instruments have been deployed as part of ongoing research. Mariners transiting the area are advised to refrain from anchoring, grounding, or fishing near the marked coordinates, and to navigate with care. The charts affected are NZ 42, NZ 43, and NZ 4314.
Further south, Milford Sound / Piopiotahi is the subject of updates to chart NZ 7621. The revisions reflect new construction, revised depths, and changes to navigation aids in the vicinity of the ferry terminal at Deepwater and Freshwater Basins. A new Light List entry, numbered 4465.5, has been added for the Fresh Water Basin Breakwater Head.
The International Hydrographic Organization (IHO) has made available a free dataset designed to help skippers verify that their ECDIS (Electronic Chart Display and Information System) correctly displays new chart features. The tool is available for download from iho.int, and mariners are encouraged to run the appropriate checks and report any issues to their system provider.
Updates to HF radio frequencies used by Taupō Maritime Radio (ZLM) are also included in this edition, supporting maritime communication over distances of up to 1,000 nautical miles.
On the publications side, both the New Zealand Nautical Almanac and Light List have received amendments covering several locations, among them Marsden Cove, Sinclair Point, One Tree Point, Shell Cut Reach, and Milford Sound. Outdated entries have been removed to improve accuracy. Mariners working from printed editions will need to apply these corrections manually.
The notice also serves as a reminder that local harbourmasters publish their own Local Notices to Mariners. These should be consulted regularly, particularly in busy areas such as Auckland and other high-traffic regions.
Any one of these updates might look routine on its own, but the Hydrographic Authority is clear that precision in navigation data carries real consequences. A newly deployed instrument, a revised depth figure, or a changed buoy position can all become deciding factors when a vessel is operating close inshore or in conditions of reduced visibility. Skippers who come across new or suspected hazards are encouraged to report them to ntm@linz.govt.nz, and current coastal and NAVAREA warnings can be found through Maritime NZ and AMSA.
