WAYPOINT - GNSS interference, workload and fatigue

27 Jan 2026 The Navigator

Managing a new addition to the established workload – and what maritime regulation can learn from civil aviation

Responsibility for fatigue management of a ship’s crew lies largely with the Master of the vessel. They must implement a fatigue management plan in accordance with their company’s safety management systems. These should in turn adhere to the ISM Code. Problems related to fatigue are often exacerbated under stressful navigational conditions, particularly if lean manning systems mean there are fewer crew members available to offer support on the bridge.

A recent investigation undertaken on behalf of the Royal Institute of Navigation explored the impact of increased workload and stress resulting from GNSS interference.

Mariners were asked to estimate the impact of GNSS interference on their workload. Of 245 mariners who responded to the survey, just 25% reported little to no impact on their workload from GNSS interference. Contrastingly, 42% reported a moderate impact and nearly 33% reported a large impact on their workload.

Stressful situations need support

A further question asked respondents to describe the actions they took to counter any increase in workload. Over 60% of 241 answers supplied required calling on additional people. This include:

  • Calling the Master to the bridge;
  • Asking an AB to steer the ship during periods when the autopilot was not functioning normally;
  • Seeking assistance to help silence alarms;
  • Seeking assistance to adjust equipment settings to compensate for interference or revert to traditional navigation;
  • Calling an engineer to the bridge to check equipment.

All of these would require additional people on the bridge, potentially disturbing someone else’s rest hours.

One survey respondent wrote, “No actions possible, as extra crew cannot join the vessel in the middle of the ocean. All crew are already fixed into their watches and extra workload is inadvisable.”

This suggests that their vessel is very lean-manned. While it is hoped that they close up extra personnel for a fog watch, this is a clear example of a situation where safety and lack of rest are at odds with one another.

More than half of those who replied said GNSS interference had a large impact on the safety of the vessel. Even more stated it had a moderate or large impact on their personal safety, physical or psychological well-being. In demanding situations like this, it is reasonable to conclude that mariner fatigue could present a critical risk to operational effectiveness and even safety.

Managing fatigue at sea and in the air

Let’s compare mariner fatigue with fatigue management for civil aviation pilots. Civil aviation pilots and crews have stringent and uniformly enforced working-hour and rest regulations. The aviation sector places the onus of compliance on the airline rather than the pilot. By contrast, maritime responsibility for fatigue management lies primarily with the ship’s Master.

Airlines apply working regulations rigorously, using a formal fatigue risk management system to manage pilots’ hours. Work and rest periods are extensively monitored with limits on: actual flight hours per flight/month/year; total flight duty hours per duty period and per month; working hours per year and rest hours at base and away, per previous duty length and per week.

The maritime working environment is quite different, so no direct read-across is possible. However, this illustrates the extent to which operational and duty hours must be controlled to prevent safety being compromised.

Ivana Carrioni-Burnett FRIN is a marine pilot at the Port of London Authority and Chair of the Maritime Navigation Group at the RIN

Return to listing