Miscellaneous Notices to Mariners
4.1 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.
All nautical charts in the scale 1:50 000 or larger are projected in Gauss conform cylinder projection (Gauss-Krüger). Nautical charts in scales less than 1:50 000 are usually constructed in a Mercator projection.
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
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.
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. 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.
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.
Leading lines indicate that waters are commonly used as fairways.
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.
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.
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.
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.
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.
A rock awash is a rock which lies between chart's vertical datum and 0.5 meters below chart's vertical datum.
A rock is covered and uncovered by water. Its height is above the chart's vertical datum.
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.
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.
The coastline (the border between sea and land) in Norwegian charts is defined to be Mean High Water.
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.