by John Franklin

A Growing Problem

The purpose of this article is to bring to the attention of the recreational cruising community the increasing problem of interference with GNSS/GPS transmissions on which we have all become dependent.

GPS – Global Positioning System – was a development of the US Department of Defense (DOD) in the 1970s with the system becoming fully operational in 1993. Other similar systems now exist, namely Glonass (Russian),  Galileo (EU) and BeiDou (China).

All work in a similar manner and collectively are known as Global Navigation Satellite Systems (GNSS) which is a general term describing any satellite constellation that provides positioning, navigation, and timing (PNT).

GNSS satellites are placed in a medium Earth orbit (MEO) of around 20,000 km which means they circle the earth approximately every 12 hours. The electronic signal emanating from a satellite is very weak electronically and consequently is easily interfered with over a local receiving area by broadcasting a stronger false GPS signal.

When this is done maliciously it is known as “spoofing”. Essentially, this misleads the GPS receiver into believing it is located somewhere it is not, resulting in the device providing inaccurate location data.

A related phenomenon is when a broadcast signal contains noise or interference on the GPS frequency which overwhelms the true GPS signal and the receiver is unable to register a position. This is known as GPS jamming.

Increase in incidents

Until recently instances of spoofing and jamming were relatively rare but during 2024 there was almost an explosion of incidents particularly affecting the civil aviation sector. Regional areas particularly affected were “conflict zones” of the Middle East, Eastern Mediterranean, Black Sea, Ukraine, Belarus, Russia and the Baltic Sea.

The problem became so acute that it led to a multi-agency investigation and report by the OPS GROUP¹ published in September 2024. This report considered only instances of spoofing in the aviation sector but one of the most startling revelations was that in one month alone in 2024 there were 41,000 reports of GPS interference from civil aircraft.

This report had such an impact on the navigational community that the Royal Institute of Navigation (RIN) in August 2025 formed a working group to study the effects of GPS spoofing on the maritime sector led by the RIN Director, Dr Ramsay Faragher. In introducing the formation of the working group the RIN stated:

“Interference has been pervasive for years now in areas such as the Baltic Sea and the Black Sea. In the Strait of Hormuz alone, almost 1000 ships per day experience GNSS interference, impacting crew safety and the security of their cargo. Collisions and groundings are a very real threat, with the Frontier Eagle and MSC Antonia accidents being the most recent examples.  The RIN Maritime Spoofing Working Group is appealing to ALL mariners to report to it any recorded instances of GPS spoofing or jamming and specifically to complete their survey.”

A Very Real Threat

GPS interference is a very real threat. It is here to stay and at present it seems there is little we can do to counter it. A White Paper published by Spirent² shows that a working spoofer may be easily constructed by an amateur using readily available components for a couple of hundred dollars. With conflict areas spreading throughout the world and an increase in drone warfare, GPS interference is very likely to become more commonplace.

Fortunately, areas in which maritime GPS interference is presently being experienced, with the possible exception of the Baltic Sea, are not popular recreational sailing destinations, but recreational mariners need to be aware and to be prepared.

How prepared are you for loss of a reliable GPS signal? Think about it! Do you keep an hourly position log? Are you still familiar with other position fixing methods? Do you carry a sextant and know how to use it? Do you carry paper charts or know how to plot on your electronic charts?

BE AWARE, BE PREPARED

John Franklin
Yachtmaster Ocean, MRIN
Past Commodore Ocean Cruising Club
Member OCC, Cruising Club of America, Cruising Association, Royal Thames YC
Founding Director Ocean Sailing Association of Southern Africa

References

¹       Final Report by OPS GROUP on GPS spoofing September 2024
²       White Paper published by Spirent Group on GNSS Spoofing

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Related Links:

• RIN Maritime Report – Exploring GNSS Interference
• Sweden Reports Sharp Rise in GPS Disruptions Over the Baltic

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