Dear readers,

The other day I was scrolling through my monthly direct debits and got stuck on a familiar item: Nautical chart subscription. Another year, another hundred euros for up-to-date electronic nautical charts. Not that I wouldn't spend the money - safe navigation has its price. But hand on heart: doesn't it sometimes annoy you that data collected by government agencies with our tax money costs extra?

Adam Lucke, a developer, apparently had exactly the same thought when he asked himself: If the Federal Maritime and Hydrographic Agency (BSH) publishes its survey data as part of open data anyway - why doesn't someone turn it into a freely accessible nautical chart?

No sooner said than done. The result is called freenauticalchart.net and is currently causing quite a stir in the sailing world. Free online nautical charts for German waters and the Dutch Wadden Sea, automatically updated weekly, with tide forecast, tidal current atlas and plotting tools. Can be used in the browser or as an app, completely without registration or subscription trap.

Sounds almost too good to be true, doesn't it?

When I opened the tool for the first time, I was impressed. The charts look like real nautical charts - with all the familiar symbols, depths and buoys. You can plan routes, enter bearings and even construct current triangles. Particularly practical for single-handed sailors: everything works on the tablet via touchscreen. No more going down to the chart table to quickly determine a course.

I find the integration of the tidal current atlas particularly successful. A click on a BSH forecast point shows the tidal curve, and a slider lets you scroll through the hours before and after high tide on Heligoland. Nautical chart, tide calendar and current atlas in one tool - that's very convenient.

This is a great tool for planning trips at your desk at home or as a training tool. Map sections can even be printed out, including coordinates and scale. And installed as a progressive web app, the whole thing also works offline.

But then came the "but".

Following our publication on freenauticalchart.net, Thomas Dehling from BSH got in touch. His message was unmistakable: the open data nautical chart data on which the tool is based are not for safe navigation released.

Wait a minute, I thought. The same data that commercial providers use should not be suitable for navigation?

Not quite. The BSH provides two fundamentally different data sets. The quality-assured navigation data - checked according to international standards, with all shallow areas guaranteed - only goes to licensed partners. The freely available open data bathymetry data, on the other hand, is intended for other purposes: offshore industry, storm surge forecasting, anglers. "We give no guarantee that this is nautically correct," says Dehling.

Particularly controversial: the positions of buoys and beacons in the open data services are also not maintained with the same timeliness as in official nautical charts. If a navigation mark is moved, the change appears in the notices to mariners and in the official charts - but not necessarily at the same time in the open data services.

That's sneaky. Because at first glance, everything looks correct. The deviations only become apparent in direct comparison - for example in the case of depth data, which in the Wadden Sea can sometimes deviate from the licensed data by more than half a metre.

What does this mean for us sailors?

The way I see it: Freenauticalchart.net is a great tool for trip planning, overview and training. It's fun to work with and it costs nothing. It is definitely suitable as a backup navigation tool or for rough orientation in the event of a GPS failure.

But - and this is an important but - it does not replace official nautical charts. Especially not in critical areas such as the Wadden Sea, where centimetres can make the difference. The Ship Safety Ordinance still requires up-to-date paper charts or authorised electronic nautical charts on board. And the notices to mariners remain indispensable.

It's a bit like Wikipedia: Great for an initial overview and often surprisingly good. But when it really comes down to it, you need reliable sources.

Nevertheless, I am glad that freenauticalchart.net exists. It shows what is possible with open data. It democratises access to nautical chart information. And it poses uncomfortable questions to the commercial nautical chart industry: Why does it take weeks or months for new BSH data to become available when a hobby developer can do it fully automatically?

Perhaps that is the greatest value of this project: it brings movement to a market that urgently needs movement. And it reminds us that navigation is more than just blindly relying on a display. It requires critical thinking, multiple sources of information - and, when in doubt, still a view from the cockpit.

Do you use freenauticalchart.net for planning? Or do you rely exclusively on commercial providers? I look forward to hearing about your experiences.

Hauke Schmidt

YACHT editor

*** Vote/click to see the result! ***

Recommended reading from the editorial team

• Click here for all previous "YACHT Week" columns