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Miscellaneous Notices to Mariners

1 Important attachments to the Efs

The attachments will be published in their entirety in the first edition of the Norwegian Notices to Mariners, Etterretninger for sjøfarende (Efs), every year.

It is important that you as seafarers regularly read these attachments, as changes may occur.

The Norwegian Hydrographic Service emphasizes that the complete pdf version of the Efs is the official document. Professional users/subscribers are responsible for downloading the latest pdf version of the Efs from the Internet service at

1.1 Updating and Printing of Charts

The year of publication is shown in the title block. This information will help the mariner in judging the reliability of the chart. As charts are subject to frequent changes, they are reprinted regularly.

The month and year of printing as well as the latest Notices to Mariners it is updated to,is shown in the lower left-hand corner of the chart. See example below.  "POD: 22. Dec 2016. Corrected to "Efs" No 23/16." means that map file is generated 22.12.2016 and the notices published in Efs no. 23/16 is corrected in the chart.

Hydrographic charts on paper are now sold only as POD-Charts (Print on demand) and must be ordered from authorized POD dealers. Charts are subject to frequent changes, and important amendments are continuously published in the Norwegian Notices to Mariners, Etterretninger for sjøfarende (Efs).

It is therefore the responsibility of the mariners to keep their charts updated in accordance with Efs after the date of printing. A Norwegian chart is updated when all corrections from the Efs concerning that chart are applied.

Overview with printing dates for Norwegian charts (pdf).

1.2 Terms Used When Issuing Charts

The following terms are used when referring to the issue of charts. The text is in accordance with the International Hydrographic Organization's (IHO) publication S-4 "Chart Specifications of the IHO", Section B-100, point 128.

1.2.1 New Chart

The “New Chart” is the first publication of a chart that either:

  • covers an area not previously charted to the scale shown.
  • includes new coverage for an existing chart.
  • includes a modernised version of an existing chart (with regards to symbols and general presentation).
  • includes the adoption of an international (INT) or national chart, first published by another nation.

A new chart renders any existing version of the chart obsolete.

1.2.2 New Edition (NE)

A new edition of an existing chart contains amendments of navigational importance derived from newly received information. It will include additional changes to those previously published in the Norwegian Notices to Mariners, Etterretninger for sjøfarende (Efs).

A new edition will render the existing edition of the chart obsolete.

1.2.3 Reprint

Since the Norwegian Hydrographic Service stopped printing paper charts in March 2015, the term ‘reprint’ has received a new meaning. The whole chart portfolio (231 charts) is now offered as updated PDF files through the POD service twice per month. All charts that are not announced as being ‘new editions’ are considered to be ‘reprints’.

Reprints consist of a new print of the current edition of a chart incorporating no amendments of navigational significance other than those previously published in the Efs (if any). It may however contain amendments from other sources provided they are not essential to navigation.

Previous printings of the current edition of the chart remain in force.

1.3 Quality in Norwegian Charts and Electronic Charts

The Norwegian Hydrographic Service aims to provide charts of the entire Norwegian coast based on modern source data. In Hordaland and the northern part of Norway there are still charts partly based on surveys that are up to 100 years old. To conduct new surveys and provide modern charts of these areas has high priority.

1.3.1 Mixture of old and new depth data

To ensure optimal use of resources, the Norwegian Hydrographic Service has conducted external market research in order to ascertain users' evaluation of how remaining areas should be prioritized. The recommendations are taken into account in the production plans. This means that there will be a mixture of old and new depth data within the same ENC or paper chart.

1.3.2 Source diagram in charts

The source diagram printed in the chart title box shows when the survey was performed and the quality of the depth data. This provides an indication of the accuracy of the product. Areas surveyed before about 1960 did not receive full seafloor coverage and depth anomalies may be expected.

There may be undiscovered depths in older surveyed areas. Caution must therefore be taken when sailing in these areas. It is dangerous to sail outside marked areas/recommended track.

1.4 Quality of Norwegian Charts and Electronic Charts in the Waters Around Svalbard

Uncritical use of older charts and modern positioning systems (like GPS) can, because of discrepancies etc. related to the datum, lead to serious mistakes (several hundred meters) during navigation. This further means that the safety margin that sailors should always apply may not be in place as expected.

In some of the older charts, information is given showing the displacement between the graticule of the chart and the World Geodetic System (WGS-84).

New charts for the area are made in accordance to the World Geodetic System (WGS84), while new prints of the older charts retain the existing graticule.

The Norwegian Hydrographic Service reminds the users that the paper charts in the area are on a scale of 1:100 000 or less, and that these charts often form the basis for electronic charts over these waters.

For general information about the quality of the charts around Svalbard, reference is made to The Norwegian Pilot, Volume 7 and the information given in each chart.

The users should be aware that all given corrections (shifts in datum) must be considered to be approximate. The coastline can have considerable discrepancies when compared to the graticule of the chart. Furthermore, the lines of survey for these waters are spaced out to such a degree that the occurrence of undiscovered shoals and rocks cannot be excluded.

Accordingly, navigation in these waters requires extra caution. The navigator should, in keeping with established navigational traditions, use all accessible navigation aids (including radar), continuously compare the observations from the different aids, remain vigilant and ensure that the navigation at all time is carried out applying a sufficient safety margin.

Use of electronic charts does not relieve the navigator from these tasks, and will still require the same professional and critical attitude as with traditional navigation using paper charts.

1.4.1 Changes in glacier fronts and coastline – glaciers used in conjunction with leading lines

The glacier fronts seawards are continually changing. In general, the glacier fronts are receding: observations exist where the glaciers have receded several hundred meters during the last decades.

It is also usual that the glaciers have shorter periods when advancing considerably ("surging glaciers"). Large quantities of ice then move downward from the top of the glacier and collapse below. For this reason contour lines and terrain close to the glacier can deviate from contour lines on the chart. As an example the Fridtjovbreen in van Mijenfjorden advanced about four kilometres from autumn 1995 and the next two and a half years.

In the chart the glacier fronts seawards can refer to a certain year, but such information does not always exist. Changes in the front of a glacier can cause a considerable difference between the existing front and the charted front. In areas where the glacier fronts have receded compared to fronts shown on the chart, no depth information exists.

Also the coastline can change, in particular close to large rivers. The user should bear this in mind and ensure that the utmost care is taken when navigating close to glacier fronts and river estuaries.

Glaciers are in some cases used as a reference in conjunction with leading lines. These can be old and well-known points which have been used for decades. Changes in the form and outline of glaciers might, however, cause changes in the reference point. Where glaciers are used as reference points great care must be taken during the navigation, and it must always be done in conjunction with other navigation aids.

1.4.2 Unsurveyed areas

Surveys are incomplete in some areas of Svalbard. Large areas are not surveyed at all. These areas are presented as white areas limited by a red dashed line and the text "Unsurveyed". We will strongly advise against any navigation in these areas – even if some soundings and underwater rocks are shown. The areas should be referred to as unsurveyed.

Areas inside the 50 meters depth contour in areas with old surveys are not safe. We advise against all navigation in such areas.

In newly surveyed areas of Svalbard, the surveying is performed at depths deeper than 3 meters only. Shallow areas are not surveyed.

Refer to the Warnings and Source diagram in the Charts.

1.5 Zones of Confidence – ZOC diagram

In digital charts the data quality is specified in Zones of Confidence (ZOC).

The ZOC diagram describes the quality of the bathymetry in the different areas. There are five quality categories in the ZOC diagram (A1 to D).

Until autumn 2013, mainly category B and C are used for Norwegian coastal waters based on the following classifications: ENCs with source data from older surveying (before 1960) are given ZOC value C, while ENCs with source data from surveying younger than ca 1960 are given ZOC value B.

From 1st of January 2014 the areas measured with multibeam sonar and which otherwise meets the requirements will be given the categories A1 or A2. The delimitation of the different zones will be added in the ENCs to always show which zone you are in.

Navigators must show great care when using (D)GPS and electronic charts in areas with older surveys as accuracy and completeness of the depth indicators are not in accordance with modern standards.

Additionally, the navigators should ensure that navigation at all times is conducted with good safety margins and in accordance with proper navigational practices.

For a full description: S57 IHO Transfer Standard for Digital Hydrographic Data.

ZOC Category
ZOC1 Position Accurancy2 Depth Accurancy3 Seafloor Coverage Typical Survey Characteristics5
A1 ± 5 m + 5% depth = 0.50 + 1%d Full area search undertaken. Significant seafloor features detected4 and depths measured. Controlled, systematic survey6 high position and depth accuracy achieved using DGPS or a minimum three high quality lines of position (LOP) and a multibeam, channel or mechanical sweep system.
Depth (m) Accurancy (m)


± 0.6
± 0.8
± 1.5
± 10.5

A2 ± 20 m = 1.00 + 2%d Full area search undertaken. Significant seafloor features detected4 and depths measured. Controlled, systematic survey6 achieving position and depth accuracy less than ZOC A1 and using a modern survey echosounder7 and a sonar or mechanical sweep system
 Depth (m) Accurancy (m)
± 1.2
± 1.6
± 3.0
± 21.0
B ± 50 m = 1.00 + 2%d
Full seafloor coverage not achieved; uncharted features, hazardous to surface navigation are not expected but may exist. Controlled, systematic survey achieving similar depth. But lesser position accuracies than ZOCA2, using a modern survey echosounder5, but no sonar or mechanical sweep system.
Depth (m) Accurancy (m)

± 1.2
± 1.6
± 3.0
± 21.0

C ± 500 m = 2.00 + 5%d Full seafloor coverage not achieved, depth anomalies may be expected. Low accuracy survey or data collected on an opportunity basis such as soundings on passage.
Depth (m) Accurancy (m)

± 2.5
± 3.5
± 7.0
± 52.0

D worse than ZOC C worse than ZOC C Full seafloor coverage not achieved, large depth anomalies may be expected. Poor quality data or data that cannot be quality assessed due to lack of information.
U Unassessed – The quality of the bathymetric data has yet to be assessed


To decide on a ZOC Category, all conditions outlined in columns 2 to 4 of the table must be met.

Explanatory notes quoted in the table:

1 The allocation of a ZOC indicates that particular data meets minimum criteria for position and depth accuracy and seafloor coverage defined in this Table. ZOC categories reflect a charting standard and not just a hydrographic survey standard. Depth and position accuracies specified for each ZOC category refer to the errors of the final depicted soundings and include not only survey errors but also other errors introduced in the chart production process. Data may be further qualified by Object Class 'Quality of Data' (M_QUAL) sub-attributes as follows:

a) Positional Accuracy (POSACC) and Sounding Accuracy (SOUACC) may be used to indicate that a higher position or depth accuracy has been achieved than defined in this Table (e.g. a survey where full seafloor coverage was not achieved could not be classified higher that ZOC B; however, if the position accuracy was, for instance, ± 15 metres, the sub-attribute POSACC could be used to indicate this).

b) Swept areas where the clearance depth is accurately known but the actual seabed depth is not accurately known may be accorded a 'higher' ZOC (i.e. A1 or A2) providing positional and depth accuracies of the swept depth meets the criteria in this Table. In this instance, Depth Range Value 1 (DRVAL1) may be used to specify the swept depth. The position accuracy criteria apply to the boundaries of swept areas.

c) SURSTA, SUREND and TECSOU may be used to indicate the start and end dates of the survey and the technique of sounding measurement.

2 Position Accuracy of depicted soundings at 95% CI (2.45 sigma) with respect to the given datum. It is the cumulative error and includes survey, transformation and digitizing errors etc. Position accuracy need not be rigorously computed for ZOCs B, C and D but may be estimated based on type of equipment, calibration regime, historical accuracy etc.

3 Depth accuracy of depicted soundings = a + (b*d)/100 at 95% CI (2.00 sigma), where d = depth in metres at the critical depth. Depth accuracy need not be rigorously computed for ZOCs B, C and D but may be estimated based on type of equipment, calibration regime, historical accuracy etc.

4 Significant seafloor features are defined as those rising above depicted depths by more than:

a. <40 m 2 m
b. >40 m 10% depth

A full seafloor search indicates that a systematic survey was conducted using detection systems, depth measurement systems, procedures, and trained personnel designed to detect and measure depths on significant seafloor features. Significant features are included on the chart as scale allows. It is impossible to guarantee that no significant feature could remain undetected, and significant features may have become present in the area since the time of the survey.

5 Typical Survey Characteristics - These descriptions should be seen as indicative examples only. 19 S-57 Supplement No. 2 June 2009

6 Controlled, systematic surveys (ZOC A1, A2 and B) - surveys comprising planned survey lines, on a geodetic datum that can be transformed to WGS 84.

7 Modern survey echo sounder - a high precision single beam depth measuring equipment, generally including all survey echo sounders designed post 1970." (See also 1.Cl.42).

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