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Miscellaneous Notices to Mariners

4 Nautical Charts

Nautical charts are the foundation for safe navigation. When navigating narrow channels, charts in the largest scale available should always be used as these give the best and most detailed information about the waters. Smaller scale charts are very simplified and are not edited to support navigation in coastal waters.

The publication date can be found in the title area. This date will provide the user with a guideline to how reliable the chart is. Please check the "Printing and Maintenance" section for further information.

4.1 Reliability

Due to the rapid development of both shipping and electronic navigational aids, the demand for reliability in nautical charts is now greater than ever. The chart reliability is very much dependent on the technology available to the hydrographical service.

Charts based on older surveys do not fully meet today's reliability standards. Therefore, Norwegian Hydrographic Service frequently receive discrepancy reports. These reports are promptly handled.

If required, a notice will be published in the Etterretninger til sjøfarende (Efs). Nautical charts are updated at the next print.

4.1.1 Projections

All nautical charts in the scale 1:50 000 or larger are projected in Gauss conform cylinder projection (Gauss-Krüger). (Older charts may also be constructed in other projections.)

Nautical charts in scales less than 1:50 000 are usually constructed in a Mercator projection.

4.1.2 Chart Scale

Norwegian Hydrographic Service publishes navigational charts over Norwegian and bordering waters. The charts are mostly based on Norwegian hydrographic surveys.

Navigational charts are published in the following scales:

  • Main chart series 1:50 000 – 1:100 000
  • Harbour chart series 1:5 000 – 1:25 000
  • Coastal chart series 1:200 000 – 1:350 000
  • General chart series 1:700 000 – 1:10 000 000

4.1.3 Chart datum

From Utsira and northwards, including Svalbard, the chart datum (vertical) is identical to "lowest astronomical tide" (LAT). In Oslofjorden (north of Drøbaksundet) the chart datum is 30 cm below LAT, and between the Swedish border and Utsira the chart datum is 20 cm below LAT.

Meteorological conditions can cause depths to be less than specified in the chart. More information can be found in the publication Tide Tables for the Norwegian Coast and Svalbard (Tidevannstabeller for den norske kyst med Svalbard) and in the Norwegian pilot guide sailing directions, Den norske los, Volume 1, Alminnelige opplysninger.

4.2 Symbols and Abbreviations

The publication Symbols and Abbreviations on Norwegian Maritime Charts provides an overview of symbols and abbreviations used for Norwegian nautical charts. The text is in both Norwegian and English.

4.2.1 Place names

In some charts the spelling of place names are out dated. Place names are currently under revision and creation.

When new releases of charts are published, all place names will be revised and updated.  It will therefore take a while before all the charts are updated.  There is currently a transition period with maps and publication using both the old and new spellings of certain place names.

In new editions of charts place names a will be updated in accordance with the laws on place names.

4.2.2 Leading Line

Leading lines indicate that waters are commonly used as fairways.

4.2.3 Ferry route

To inform mariners of crossing traffic, ferries are marked on the chart by the contours of a red ferry along a dashed line. This symbol is not to be regarded as a recommended track.

4.2.4 Overhead- and Submarine Cables

Overhead cables, telephone and power lines that cross salt water are inserted onto the nautical charts after if Norwegian Hydrographic Service is notified about them. Notices about new cables are frequently issued in Efs.

As both overhead and underwater cables may carry very high voltages, it is important that the navigator show extreme caution when navigating near them. The navigator should also be aware that new cables may not be displayed in the chart.

Underwater and overhead cables which are installed after the latest print of the chart have to be inserted manually.

4.2.5 Depth Contours

The depth contours have been drawn through points with the same depth, and have then been generalized. Thus, the contours may not always be accurate, but they do show the nature of the topography of the sea floor. By generalizing the depth contours, the line is always moved towards deeper waters to ensure safe navigation.

In areas where the topography is complicated, normal cartographic practice is to merge or generalize the depth areas. This is very common in the complex Norwegian waters.

4.2.6 Soundings

A sounding is the depth in a position relative to the chart's vertical datum. Its value is a positive number. Its position is the centre of the number.

4.2.7 Underwater rocks

An underwater rock is an area of limited size which stretches towards the surface, but is deeper than 0,5 m below the chart's vertical datum.

0 – 9,9 m are displayed with decimals.

10 – 20 m are rounded down to the nearest meter

> 20 m are displayed as soundings, in italics.

4.2.8 Rock awash

A rock awash is a rock which lies between chart's vertical datum and 0.5 meters below chart's vertical datum.

4.2.9 Rock

A rock is covered and uncovered by water. Its height is above the chart's vertical datum.

4.2.10 Danger Line

The Norwegian "danger line in general" is still in use in some areas of several of our charts.

In sheltered waters, it is a dotted line which indicates an approximate depth of 6 m.

In more open waters, it may be drawn in deeper waters, normally 6 to 20–30 m.

4.2.11 Intertidal Areas Above Chart Datum

The area of the seafloor between 0,5 m below the chart's vertical datum and the coastline. This area is limited by the Charts Low Waterline.

4.2.12 Coastline

The coastline (the border between sea and land) in Norwegian charts is defined to be Mean High Water.

4.2.13 Depth Over Wreck

Wrecks and large debris on the seafloor may over the course of time have shifted so much that the depth above such wrecks may be less than the charted depth.

4.3 Tidal Waters

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

4.3.1 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.

4.4 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

More information on the Norwegian tides can be found at Se havnivå.

Download illustration showing reference levels in Norwegian charts (Norwegian text), pdf 87 kB (opens in a new window).

More information on the Norwegian tides can be found at:

www.sehavniva.no

4.6 Submarine Cables, Overhead Cables and Submarine Pipelines

Both submarine and overhead cables can carry very high voltages, and mariners should be careful when navigating near them. They should also be aware that submarine and overhead cables may not be displayed in the charts. The vertical clearance may also vary due to extreme weather conditions.

4.6.1 Damage to Submarine Cables

Mariners should avoid anchoring and fishing in areas where a submarine cable is displayed on the chart. Anchors and fishing gear can cause severe damage, and disrupt telecommunications or the power supply.

4.6.2 Damage to Pipelines

Gas from a damaged oil or gas pipeline could cause an explosion, loss of a vessel's buoyancy, serious pollution or other hazards.

Pipelines on the seafloor are not always buried and their presence may effectively reduce the charted depth by as much as 2 meters. They may also span seabed undulations and cause snagging, putting a vessel in severe danger.

Trawling across pipelines at angles of 45° or more is recommended.

4.7 Marine Farms. Moorings

Fishing within 100 m, and sailing within 20 m of a marine farm is prohibited.

The chart symbol for a marine farm is used only where a license has been given by the Directorate of Fisheries. A marine farm may not be located in the given position as one company may have been given several licenses and alternate between these locations. Some marine farms may not be charted.

The moorings may stretch for several thousand meters from the marine farm. Not all of them are displayed in the charts.

Additional information can be found at the Directorate of Fisheries' website.

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