GPS jamming in the Baltic and North Sea: what to do?

For several years now, yachtsmen, fishermen and commercial shipping have reported disrupted satellite signals in the Baltic, especially its eastern part, and increasingly in the North Sea too. GNSS jamming makes the signal drop out. Spoofing is worse, because the plotter carries on showing a confident but wrong position, sometimes miles inland. AIS targets can be wrong as well, since other ships rely on the same positioning. Coastal states publish warnings through NAVTEX and their navigational warnings, and the UKHO publishes navigational warnings that can include GNSS interference.

A disturbance often shows up in small contradictions: a position that does not fit the heading, a speed over ground that does not match the log, a ship on AIS standing on dry land. That is when traditional seamanship returns. Carry a paper chart of the area, write position, course and log reading into the logbook at regular intervals, take bearings of landmarks and buoys with a hand bearing compass, and work up a dead reckoning position from course, time and speed. Depth sounder and radar, where fitted, help to cross check. The RYA teaches these skills in its navigation courses, and they are worth refreshing before a Baltic cruise.

For insurance, what counts is how you navigated. Running aground because of a false GPS position is a grounding like any other, so check whether your policy treats grounding as an insured accident and what it says about negligence. An owner who relies solely on the plotter despite published warnings, with no chart and no cross check, may face the argument that the loss was caused by gross negligence, and depending on the wording that can reduce or remove the claim. A properly kept log with positions and bearings is your best evidence after an incident.

Worth remembering

If you can work up a dead reckoning position, you get in without GPS.