Miscellaneous Notices to Mariners
4.2 Reference Level for Vertical Clearances
The reference level for vertical clearances in Norwegian charts is the highest astronomical tide (HAT). Analysis has shown that the tidal levels in Norway often exceed this level. Therefore extra safety margins should be added by navigators in order to ensure safe navigation.
By increasing the safety margins by the following amounts in the designated areas, the vertical clearance should be safe:
- Inner Oslofjorden (North of Drøbaksundet): 80 cm
- From the Swedish border to Hordaland: 50 cm
- From Hordaland to the Russian border: 30 cm
Observed water levels and water level forecasts for the next days are available at Se havnivå. The service also provides tide tables and vertical reference levels.
Download illustration showing reference levels in Norwegian charts (Norwegian text), pdf 87 kB (opens in a new window).
Read more about tidal waters.