There is a joke, somewhat antiquated by modern standards, which suggests that antivirus software is developed in a two-story building: the viruses are written on the first floor, while the countermeasures are devised on the second.
Have you ever found yourself in that “magical” situation – sailing in open water, far from any navigational hazards, only to have your chart plotter insist you are currently driving down a winding road toward your ex’s house? It is a disorienting, almost surreal experience.
In our world, saturated with electronics and permeated by radio waves, such incidents are becoming increasingly commonplace. These anomalies are the result of Electronic Warfare (EW). The Baltic Sea, in particular, has become a “hot zone” where this issue has reached a fever pitch. Today, official warnings from the maritime administrations of Finland, Sweden and Estonia are issued almost as frequently as the weather forecast.
Let us examine the mechanics of this phenomenon and what it means for the modern mariner.
Two Systems under attack
Over the last decade, we have surrendered nearly all our navigational agency to tablets, plotters and smartphones. It is, undeniably, convenient and accessible – but every coin has a flip side.
Electronic interference targets the two systems we rely on the most:
GNSS Global Navigation Satellite Systems
Colloquially known as “GPS”, today, this is a multi-constellation environment including Navistar (USA), GLONASS (Russia), Galileo (EU) and BeiDou (China). They all operate on the same principle: a receiver on your boat catches a faint signal from a satellite and calculates distance to the satellite based on time-of-flight. Typically 4+ satellites are needed for a reliable fix.
AIS – Automatic Identification System
The system that exchanges course, position and vessel data via VHF frequencies. AIS lets you see vessels around and be seen.
The Two Faces of Interference
Jamming and spoofing are common forms of interference. While jamming simply aims to block the signal, spoofing is more sophisticated and evolves quickly, creating new challenges.
Jamming – the Brute Force
Jamming is essentially radio-frequency “white noise.” A jammer creates a powerful blast of static on satellite frequencies, drowning out the actual signals. It is akin to trying to hold a nuanced conversation in a roaring train carriage: words are lost and eventually, you lose the thread entirely. Your plotter will trigger a “Loss of GPS Fix” error, and may alarm and/or disengage route tracking. It is frustrating, but it is honest – you know immediately that you are blind.
Spoofing – the Sophisticated Lie
Spoofing is far more insidious. Rather than drowning out the signal, it replaces it. Spoofers may simulate one or multiple constellations depending on sophistication. A modern receiver does not blindly trust the strongest signal. It performs correlation and consistency checks. However, if a counterfeit signal is sufficiently strong and carefully synchronized, it can capture the receiver’s tracking loops and slowly “pull off” the true solution without triggering immediate alarms.
The primary danger here is the Autopilot Trap. A spoofer can “drift” your position gradually – mere meters per second. Your autopilot will obediently “correct” its course to stay on the programmed track while, in reality, it is steering the vessel elsewhere. On the screen, everything looks perfect.
Furthermore, false GNSS data can poison your NMEA 2000 backbone – feeding bad position and time to every instrument connected to NMEA network.
Separately, AIS can be manipulated too: transponders can be switched off, or false AIS broadcasts can create ‘zombie’ targets.
The View from the Second Floor: Methods of Resistance
The engineers on the “second floor” have not been idle. The escalating arms race in the ether has brought new technology to the civilian cockpit. Here are the primary lines of defense:
Two frequencies instead of one
GPS satellites transmit on two frequencies L1/1575.42 MHz and L5/1176.45 MHz. L1 has long carried the common civil service; L5 is an additional civil signal designed for higher performance and robustness. The L1 frequency is narrow, weak and now thoroughly mapped by bad actors. A jammer for L1 can be built “on a kitchen table.” Modern constellations provide additional civil signals on L5 frequency (e.g., GPS L5, Galileo E5).
L5 has higher transmitted power and much greater bandwidth than L1. It is harder to ‘smother’ and is generally more resilient to multipath reflections, improving accuracy in difficult environments. To fool a dual-band receiver, an attacker must generate consistent counterfeit signals on both bands and keep them mutually consistent over time. That’s significantly harder than spoofing a single frequency and gives receivers more ways to detect inconsistencies.
Galileo OSNMA: The Digital Key
Adding second frequency L1/L5 is a physical barrier, Galileo OSNMA is a cryptographic one. Until recently, civilian GPS was “open code” – your chart plotter receiver believed any signal that sounded right. OSNMA (Open Service Navigation Message Authentication) turns your plotter into a digital customs officer. Galileo satellites broadcast coordinates accompanied by a “digital signature.” Every few seconds, the satellite applies a unique “seal” that cannot be forged without the Galileo OSNMA signing keys; receivers verify it using certified public keys published via the European GNSS Service Centre. Even if a spoofer perfectly mimics the frequency and power, it cannot fake the math. This is a new cryptographic way to fight spoofing – introduced in 2025.
Inertial Measurement Unit
If GNSS is your eyes, the IMU is your inner ear. It is a self-contained unit of gyroscopes and accelerometers that measures rotation and acceleration in three dimensions. Unlike satellite navigation, it does not depend on radio signals – it relies purely on physics. On its own, an IMU cannot provide a perfect long-term position since inertial measurements drift over time. But when combined with GNSS in a sensor-fusion system, it becomes a powerful consistency check. If jamming occurs, a high-quality 9-axis sensor allows the autopilot to hold a course accurately for several minutes based purely on inertia, giving you time to transition to manual control.
NMEA NET Protect
This is a “firewall” for your NMEA 2000 backbone. Should spoofing compromise your antenna, the false data begins to “poison” the entire network. NET Protect analyzes traffic and blocks suspicious packets, preventing them from hijacking your autopilot or sensors.
Practical Advice: Plan “B”
If you are traversing the Baltic or any other contested region, it is wise to go old school.
Paper Charts are not anachronisms – and they cannot be “hacked.” So it is wise to maintain the habit of plotting your position with a pencil. Sounds old school and modern at the same time.
The echo sounder – this is your “third coordinate” and your most honest sensor. If the chart says you are in 40 meters of water but the depth sounder says 5, believe the sounder.
The compass and bearings: Re-learn the art of taking a bearing on a visible lighthouse or landmark. A magnetic compass is immune to spoofing.
Radar: utilize the Overlay function. If the coastline on your radar does not align perfectly with the coastline on your chart, the might be the influence of EW.
Conclusion
We must accept that this is our current reality. Maintaining a “Plan B” is not a retro-hobby; it is a critical dimension of robustness, as we discussed in our previous piece on “Black Swans.” Technology is a tool, not an absolute truth. Let us be prepared for the electronics to lie and always verify their claims with your own eyes and basic instruments. Fair winds!
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