After the publication of our article about the free nautical chart BOOTE spoke to Thomas Dehling, Head of the Nautical Hydrography Department at the BSH, about Freenauticalchart.net and the disappearance of point soundings from BSH data. The conversation provides important clarity about the difference between open data nautical charts and official navigation products - and contains a clear warning to users of the free nautical chart.
Two fundamentally different data sets
The BSH provides two different types of nautical chart data, which are fundamentally different:
1. quality-assured navigation data (for official nautical charts): This data is specially analysed for safe navigation. They are checked for up-to-dateness, accuracy and reliability in accordance with the international standards of the International Hydrographic Organisation (IHO). Particularly important: All shallow areas are guaranteed to be included, the number of depth contours is limited so that the chart remains legible. This data is only available from licence holders.
2. open data bathymetry data (freely available): This data is provided in accordance with the Geodata Access Act and serves other purposes: morphologically correct representation of the seabed for the offshore industry, storm surge forecasting, anglers - but not for navigation. "We give no guarantee that this is nautically correct," explains Dehling.
Even navigation marks are not guaranteed to be up to date
Particularly explosive: the positions of buoys, beacons and other navigation marks in the BSH's open data services are not intended for navigation either. "We cannot guarantee that changes are included," says Dehling. If a navigation mark is moved, replaced or removed, the change appears in the Notices to Mariners (NfS) and in the official electronic nautical charts - but not at the same time in the open data services.
"That would be a huge effort. That's not what it's designed for," explains the head of department. For users of the free nautical chart, this means that even if buoys and beacons are nicely displayed on the chart, the position may be out of date or the buoy may have already been moved.
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Why two different data sets?
The difference lies in the evaluation of the survey data. When the BSH surveys the seabed, very detailed depth information is generated. Two different products are created from this:
For navigation: A special surface model that is guaranteed to contain all shallow areas and depth contours in such a way that they can be used safely by sailors and commercial shipping. Individual depth figures are specifically selected - especially the shallow areas.
For other purposes: A morphological model that reproduces the seabed as realistically as possible. "What anglers need or what you need for the offshore industry or for storm surge forecasting," explains Dehling. "Where are the holes? Where are the fish?" This data may contain depth contours, but not the guaranteed shallow areas.
Licence model and quality control
The BSH only passes on the quality-assured navigation data to fixed partners (licence holders). The reason: "If we put it online freely, then we can no longer guarantee that the data is correct, up-to-date and fulfils the quality requirements," says Dehling. "We don't know who can make what out of it."
What's more, the Federal Court of Auditors is demanding market prices for the data from the BSH. "This is nowhere near enough to cover the production costs, which are of course financed by taxes," explains Dehling. A general release of all nautical charts would be a political decision that would have to be taken at federal government level.
S-100: The future of electronic nautical charts
A look into the future: with the new S-100 standard for electronic nautical charts, even more detailed depth data will be possible. Users will then be able to display safety lines based on their individual draught - for example, a 3.5 metre line instead of just 3 or 4 metres. "The data must be good enough for this," emphasises Dehling. This function will initially be available for ships requiring equipment (ECDIS systems); so far, only pilots have been able to use it.
What does this mean for Freenauticalchart users?
The BSH's statements are clear: The free nautical chart Freenauticalchart.net uses data that is expressly not authorised for navigation by the BSH. Neither the depth data nor the positions of navigation marks are reliably up to date. The BSH does not guarantee the nautical accuracy of this data.
The fact that Freenauticalchart.net cannot replace an official nautical chart has been emphasised by developer Adam Lucke from with a warning notice right from the startwhich he confirmed to us once again. In addition, the warning must now be actively confirmed before the website can be used.
In practice, this means
- Trip planning, overview, training: Freenauticalchart.net remains a valuable free tool
- Backup navigation in the event of GPS failure: Basic orientation possible
- Safe navigation in critical areas: Not suitable according to BSH
- Replacement for official nautical charts: Explicitly not intended
- News for seafarers: It is essential to continue to observe
The attractive presentation and weekly updates of the open data sources should not hide the fact that the data is intended for other purposes. "The data that may look nice is not necessarily correct," summarises Dehling.
The sneaky thing is that the deviations are only noticeable in direct comparison with maps created from licensed data. For example, in the form of stones that have no depth information. The most noticeable discrepancies are in the soundings, which in the Wadden Sea often deviate from the licensed data by more than half a metre.
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Hauke Schmidt
Test & Technology editor
