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Miscellaneous Notices to Mariners

6 Tidal Waters

Tide tables are available at Se havnivå, our web service on sea level for the Norwegian coast.

Reference Level for Depths and Heights in the Tidal Tables

The vertical datum in Norwegian charts is based on the lowest astronomical tide (LAT). LAT is determined by measuring the tides over the last 19 years, and picking out the lowest tide. In areas where the tidal contribution is relatively small compared to the meteorological contribution, an extra safety margin has been added so that the datum is lower than LAT.

For Norwegian waters, the vertical datum is as follows:

  • From Utsira and north to the Russian border (including Svalbard) the datum equals LAT.
  • From the Swedish border to Utsira, the datum is 20 cm lower than LAT.
  • In inner Oslofjorden north of Drøbaksund, the datum is 30 cm lower than LAT.

This definition of the vertical datum was introduced into the Norwegian charts in January 2000. The datum of charts made prior to this date refer to Mean High Water Spring.

On the Swedish side of nautical chart no.1 the soundings refer to a different datum, and they are approximately 60 cm shallower than the Norwegian ones. When navigating Swedish waters, Swedish charts should be used.

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