Further warnings about GPS disruptions
There have been increasing reports of satellite navigation malfunctions in the Baltic Sea region for some time now. This should prompt sailors to review their own navigation procedures.
The Finnish Transport and Communications Agency, Traficom, has reported ongoing disruptions to satellite navigation and mobile communications. According to the agency, GNSS disruptions have increased in the spring of 2026. With regard to shipping, Traficom specifically identifies the eastern Gulf of Finland as a relevant area and advises boaters not to rely solely on their chartplotters and to carry a paper nautical chart.
Estonia has also issued a warning about increasing GNSS interference in the Gulf of Finland. The authorities point out that time and position data from satellite systems are used in many navigation systems. Interference can therefore not only affect position displays, but also impact other on-board systems, such as autopilot functions or AIS data.
In Sweden, the Swedish Maritime Administration had also warned of GPS interference in the Baltic Sea. The YACHT reported on the Warning from the Swedish Maritime Administration regarding widespread GPS disruptions. Among other things, it recommends alternative methods of position fixing, up-to-date paper nautical charts and monitoring navigational warnings.
In practical terms, the cause is of secondary importance at first glance. Whether it is widespread GNSS interference, a faulty antenna, a software issue, a power cut, an overheated tablet or a flat battery: what matters is whether the crew knows how to cope when the electronic position is missing or no longer reliable.
When the plotter is running but isn't working properly
A GPS problem doesn’t always start with a black screen. That’s precisely what makes it dangerous. The plotter may continue to run whilst displaying incorrect or implausible data. The yacht then jumps around on the electronic chart, appearing to be next to the fairway or even on land. The ground speed fluctuates wildly, even though the yacht is travelling at a steady pace. The track zigzags, the estimated time of arrival changes erratically, or several devices suddenly show different positions.
Checking the satellite display can be helpful. If only a few satellites are being used, or if the accuracy shown fluctuates significantly, the crew should scrutinise the position data. Even more important is checking against reality: does the position match the buoy ahead? Does the heading towards the fairway match the compass reading? Does the water depth correspond to the chart? Is a landmark located where it should be according to the electronic chart?
Even AIS is no substitute for visual observation in such situations. The positions of other vessels are also based on satellite data. If GNSS data is disrupted or tampered with, AIS targets may also become implausible. AIS remains useful, but it should be cross-checked against visual observation, radar, compass heading and a healthy dose of scepticism.
The most important rule is: don’t wait until things have completely broken down. If you carry out regular checks during normal operation, you’ll spot any glitches in the electronics sooner. Navigation doesn’t just start when the plotter fails. The YACHT-An account of GPS malfunctions and a return to map and compass.
Preparation begins before setting sail
The best aid in the event of a breakdown is on the chart table. An up-to-date paper nautical chart of the area, a pencil, an eraser, a compass, a protractor or navigation ruler, and a working compass are all part of the basic equipment. The YACHT guide explains which materials are useful for chart work You will need this navigation kit for map work. A hand-held compass is particularly useful when you need to determine your location without GPS.
Before setting sail, you should do more than just enter the day’s route into the chartplotter. It is a good idea to draw up a brief, traditional navigation plan: where are the narrow passages, shoals, traffic separation zones or fairways? Which buoys, beacons, jetties, headlands, church towers or distinctive buildings are suitable as landmarks? Where are there safe alternative harbours, anchorages or open water in case navigation becomes more difficult? The YACHT article is ideal for preparing for the leg Routing: planning the day’s route before setting off.
It is equally important to be aware of the interdependencies on board. Chartplotters, tablets, AIS, autopilots, instrument displays and apps may all use the same GNSS source or process the same data from the on-board network. A second screen is therefore not automatically an independent backup. If several devices adopt the same incorrect position value, a false sense of security can easily arise.
One simple habit can significantly reduce the risk: regularly noting down your last known position. If you record your position, the time, your course and your route on a chart or in a logbook every 30 minutes, you won’t be left with a blank page in the event of a failure. You can then continue from this last known position.
It is also worth checking your compass before setting sail. It should be easy to read, even at night. You should be familiar with its deviation, or at least have verified that it is reasonable. Anyone who has to continue sailing without GPS needs a compass they can rely on completely.
You should keep this to hand
- up-to-date paper nautical chart of the area
- Pencil and eraser
- Compass
- Compass or protractor
- a functioning navigation compass
- Hand-held compass
- Logbook
- easy-to-read fish finder
- Plan for alternative ports or safe waiting areas
In an emergency, safety comes first
If the chart plotter or app fails or provides implausible data, the crew should not rush to adjust the settings. The situation on deck is what matters most. Reduce speed, increase lookouts, check for traffic, and, if possible, increase the distance from shoals, buoys and the edges of the fairway.
In poor visibility, heavy traffic or power surges, the need to act becomes more urgent. In such cases, a decision should be made at an early stage as to whether to continue the journey, wait it out or head for a safe place.
The next step is to note the last reliable position of the vessel. If the electronic position was still plausible a few minutes ago, it should be immediately plotted on the paper chart, along with the time. If the last position is uncertain, visual observations, water depth, compass heading and bearings can help to narrow down the likely area.
This is where dead reckoning begins. Course, speed and elapsed time are plotted on the chart. The position calculated in this way is no substitute for GPS accuracy, but it enables the crew to take appropriate action. The YACHT article explains how this method works From map navigation to compass navigation and cross-country navigation.
It is important to allow for a generous margin of error. Wind, currents, navigation inaccuracies and logging errors can cause the yacht to drift. The longer you sail without a confirmed position, the greater the uncertainty becomes. Wind and currents in particular can alter the planned course over ground, as explained in the YACHT article on Taking wind and electricity into account shows.
Continue navigating using bearings, depth soundings and waypoints
From a national perspective, the terrestrial navigation the most reliable aid. A bearing taken from a clearly identifiable object yields a position line. Two bearings taken from different objects provide an observed position at their intersection. Suitable landmarks include lighthouses, fixed navigation marks, piers, headlands, church towers, distinctive buildings or other objects that are clearly marked on the chart. YACHT summarises the basics of this in the article Terrestrial navigation: How to determine your course without technology together.
That too echo sounder It then becomes more than just a depth reading. It can help to verify the presumed location. If the chart shows a depth of twelve metres at the presumed location, but the depth sounder consistently reads three metres, something is amiss. In areas with clearly defined depth contours, depth can be a key factor in verifying your position.
Radar is, if available and the crew are familiar with it, a valuable backup. Distances to coastlines, islands, buoys or harbour jetties can be checked against the chart. Radar can be particularly helpful in poor visibility for narrowing down an uncertain position. However, this is only effective if the crew do not wait until an emergency to try out the equipment.
Without a view of the countryside, the Link navigation the navigation aid. Course, speed and time are updated from the last known position. As soon as landmarks, buoys, beacons or a distinct coastline become visible again, the position is checked and corrected. The YACHT guide also provides a concise overview Navigating without GPS: Traditional methods for emergencies.
The chart plotter is an excellent tool. However, it does not relieve the crew of their responsibility to check its data. Those who prepare charts, a compass and bearing procedures, think ahead regularly and note down the last safe location will not lose their bearings in the event of GPS interference or technical problems. The journey may then be slower and more cautious. But it remains manageable.
Lars Bolle
Chief Editor Digital
