Seaways Free Article: When GNSS fails
Navigation and seamanship when PNT fails
by Capt Sercan Perdahlı AFNI
Between 12 and 16 September last year, our vessel was loading vegetable oil at Pivdennyi and Chornomorsk, with Ghent as our discharge port. We knew that we were operating in a high risk area, and security warnings, military activities and navigation restrictions were already part of our voyage planning. But reading a security warning is one thing. Seeing the situation developing around your own vessel is completely different.
The situation started with a drone attack towards the Odesa area. Drones passed over our area and the atmosphere on the bridge changed immediately. Shortly after, we received urgent information from Chornomorsk VTS. Their traffic monitoring and radar capability had become unavailable. We understood that this was possibly connected with the ongoing attack, but of course from the vessel we could not confirm the exact technical reason. Either way, the result was clear. Shore based traffic monitoring could no longer be fully relied upon. Vessels were instructed to weigh anchor and proceed towards Sulina without delay.
GNSS
Then another problem started. We began experiencing serious GNSS interference. GPS positions became unreliable and we had indications of both jamming and spoofing. When this happens, the first thing you do is check your own equipment. Maybe one GPS has failed. Maybe there is an antenna problem. But when information from different sources starts becoming abnormal at the same time, you understand that something bigger is happening.
This is where spoofing is especially dangerous. If GPS completely fails, at least you know that you have lost it. Spoofing is different. The equipment can continue giving a position. The numbers look correct. Your ship symbol is still moving on ECDIS. But you may not actually be where it tells you that you are. Sometimes wrong information is more dangerous than no information.
Back to ‘basics’
There were alarms, communications and military activity around us. A busy bridge, for sure, but no panic. My instruction to the bridge team was simple: do not trust the GPS position for now. We knew our last reliable position. We had X-band and S-band radars. We had visual information, echo sounder and our own navigation experience. So we went back to basics.
Radar became one of our main navigation tools. We concentrated on ranges, bearings, relative movements, coastline and identifiable radar targets. Parallel indexing was very useful because it allowed us to monitor our movement without depending on the GNSS position shown on ECDIS. Dead reckoning (DR) was maintained continuously. Our last reliable position, course, speed and elapsed time became vital. Very basic navigation, maybe, but very effective. Visual lookout was also essential. Wherever possible we compared what we could physically see with what our equipment was showing.
The echo sounder gave us another independent source of information. Of course, depth cannot give an exact position, but together with charted depths, radar and DR it gave another confirmation that our track was reasonable. No single method was enough. We used all available information together and continuously cross-checked our decisions.
Working as a convoy
Soon we understood that other vessels were facing similar problems. With shore based monitoring affected and satellite navigation unreliable, maintaining an organised movement towards Sulina became very important.
Other vessels started following our movement. Eventually, four vessels were following us. Without any formal arrangement, our vessel had effectively become the convoy leader. This changed the feeling on the bridge. Navigating your own ship safely is one responsibility; knowing that four other ships are following your movement is another. Every course alteration had to be considered carefully. Speed had to remain predictable. Communication had to be clear and short. We kept it to course, speed, intentions and alterations, nothing more than necessary.
Working together
This experience reminded me about another important part of seamanship. A Master’s first responsibility is always his own vessel, crew and cargo, but seafarers also have a long tradition of helping each other when it can be done safely. Assistance at sea does not always mean a rescue operation. Sometimes another vessel needs reliable information, and sometimes it needs a reference. On the other hand, sometimes when normal navigation systems are not trustworthy, it simply needs a vessel ahead maintaining a safe track. We did not plan to lead other vessels. It just happened because the situation required it.
Maintaining skills
I am certainly not against modern navigation systems. ECDIS, GNSS, AIS and Arpa have made our work safer and more efficient. We use them every day. But using technology and completely depending on technology are not the same thing.
Normally the GPS position is always available. ECDIS shows the vessel continuously, Arpa calculates targets and AIS provides additional information. Because of this, traditional navigation skills can slowly become something we practise mainly during training or audits – until the day we really need them. An officer who has not taken manual bearings for a long time may suddenly need to do it immediately. Parallel indexing can suddenly change from a training subject into an important navigation tool. Dead reckoning becomes real again.
That night these were not examination questions. They were our navigation; and it was important that we had practised them.
Verifying information
One lesson became very clear to me after this experience. We should not train only for equipment failure. We should also train for equipment giving us wrong information. A failed GPS tells you that something is wrong. A spoofed GPS may tell you everything is normal, and that is precisely what is dangerous. A navigator must always be ready to question the electronic position. We should constantly be asking ‘GPS says we are here – but what does the radar say? What does the echo sounder show? What can we see outside? Where should we be according to our course, speed and last reliable position?’
We finally proceeded safely towards the Sulina area. When I remember that night, I remember the drones overhead, the attack towards Odesa, the VTS communication, the loss of shore based traffic monitoring and the GNSS interference. But I also remember what still worked. Radar, visual bearings, parallel indexing, echo sounder, DR, proper lookout, bridge teamwork and clear communication. And above all, seamanship.
For me, that night was seamanship in its purest form. Technology will continue developing, and we should develop with it. But we should never lose the basic navigation skills. Old school navigation is not really old. It is still navigation.
And when GNSS can no longer be trusted, the navigator must still know the way.