Marine Fatigue

Marine fatigue explained: what the rules require and what happens on watch

Key takeaways

• Fatigue at sea is regulated through rest hours, and rest hours are self-recorded. STCW and the Maritime Labour Convention both set a floor of 10 hours of rest in any 24-hour period and 77 hours in any seven days. Compliance is evidenced by the crew’s own paperwork.
• The records and the reality diverge. Port State control inspections show compliance between 90 and 99.3%. Seafarers surveyed about the same regulations report between 11.7 and 16.1%.
• The consequence lands on the lone night watch. In the MAIB’s bridge watchkeeping study, fatigue contributed to 82% of the groundings that occurred between 0000 and 0600.
• Orca AI adds an independent record of the watch. SeaPod keeps detecting and tracking surrounding traffic at any hour, without waiting for the officer of the watch to notice first.

What is marine fatigue?

Marine fatigue is a reduction in physical or mental capability caused by sleep loss, extended waking hours, disrupted circadian rhythm, or sustained workload. On board it degrades attention, reaction time, judgment, and the ability to hold a picture of a developing traffic situation. The IMO addresses it in MSC.1/Circ.1598, Guidelines on Fatigue.

That circular was approved by the Maritime Safety Committee at its 100th session in 2018 and issued in January 2019. It replaced MSC/Circ.1014 from 2001, and it sits alongside Assembly resolution A.772(18) on fatigue factors in manning and safety, adopted back in 1993. The IMO has been writing about this for more than 30 years.

The guidance runs to six modules: fatigue itself, fatigue and the company, fatigue and the seafarer, awareness and training, ship design, and the role of Administrations and port State authorities. Transport Canada groups the causes it identifies into five categories: the seafarer, on board and shore-based management, the vessel, the environment, and operational requirements.

What causes marine fatigue at sea?

Fatigue on board is rarely one thing. It accumulates.

• Watch patterns that fight the body clock. The 6-on/6-off system used on many short-sea and coastal vessels never allows a single long sleep. An uninterrupted 6-and-6 cycle lets the body partially adapt, but frequent port calls break the cycle before adaptation happens.
• Port workload. Pilotage, cargo operations, audits and inspections all land on the same officers who keep the sea watch. In a short-sea trade with voyages measured in hours, departure from the normal watch pattern is close to unavoidable.
• Noise, motion and accommodation quality. Cardiff University’s Seafarers International Research Centre found seafarers attributing insufficient sleep to vessel movement and noise, and reported that both had increased since comparable data was collected in 2011 and 2016.
• Work-related anxiety. In the same study, sleep loss caused by anxiety was most acute among senior officers, the people whose judgment carries the most weight.

What do the rest hour rules require?

Two instruments govern rest at sea, and they set the same floor by different routes.

Under STCW Code section A-VIII/1, anyone assigned duty as an officer in charge of a watch, or as a rating forming part of a watch, must receive a minimum of 10 hours of rest in any 24-hour period and 77 hours in any seven-day period. Rest may be split into no more than two periods, one of which must be at least 6 hours long, and the interval between them cannot exceed 14 hours.

The Maritime Labour Convention, 2006, Standard A2.3, lets a flag State regulate either maximum hours of work or minimum hours of rest. Both routes are legal. They are not equivalent.

The weekly gap between the two MLC routes is 19 hours. A flag State that regulates by work hours delivers a materially better-rested crew than one that regulates by rest hours, and both are compliant.

Canada’s coastal figure sits in the table as a reminder of how wide the spread gets once national regimes apply. Six consecutive hours of rest in 24 is a long way from 10.

Why do rest hour records show compliance when crews report fatigue?

Because the records are written by the people whose workload they document.

A 2024 study in Marine Policy compared port State control outcomes from inspection campaigns on hours of work and rest against a global survey of seafarers. PSC-recorded compliance ran between 90.0% and 99.3%. Seafarers reporting on the same regulations put compliance between 11.7% and 16.1%.

That gap is the single most useful number in any discussion of marine fatigue. It says the measurement instrument is broken.

Accident investigators reached the same conclusion two decades earlier. The MAIB wrote in its Bridge Watchkeeping Safety Study that, in its own opinion, “the records of hours of rest on board many vessels, which almost invariably show compliance with the regulations, are not completed accurately.”

The World Maritime University’s EVREST study, funded by the ITF Seafarers’ Trust and published in 2020, went further. It found that recordkeeping software “effectively incentivise[s] crew to adjust their records,” identified insufficient manning as the root cause of violations at peak workload, and described seafarers as “trapped in cognitive dissonance, where deviance is normalised.”

The Seafarers Happiness Index for Q2 2026 reported the same practice in crews’ own words: rest hours recorded “just for authorities and filing.”

How does fatigue show up on the navigational watch?

It shows up as one officer, alone, in the dark, asleep.

The MAIB study examined 66 accidents involving 75 vessels, drawn from 1,647 collisions, groundings, contacts and near collisions reported between 1994 and 2003. Of the 23 vessels that grounded, 11 grounded between 0000 and 0600. Fatigue was a contributory factor in nine of those 11, or 82%.

In eight of those nine, the pattern was identical.

The pattern is the point. Eight ships, one failure mode, 35% of every grounding in the study.

The MAIB also did the arithmetic on the 6-and-6 pattern. A watchkeeper on 6-on/6-off spends 84 hours on watch in a seven-day period. Add the 77 hours of rest the regulations require and 7 hours remain, one hour per day, for everything else a master or chief officer has to do. The MAIB’s conclusion was blunt: either those tasks don’t get done, or the rest hour rules get broken.

Its sole-watchkeeper grounding profile is equally specific. Of the 12 vessels that grounded with a sole watchkeeper, 84% were under 3,000gt, 92% carried only two deck officers, 75% ran aground in darkness, and all of them had clear or good visibility. Nothing about the weather made these accidents happen.

Is marine fatigue getting better?

Not by the available evidence.

Cardiff University’s SIRC surveyed 1,240 cargo ship workers and 1,202 cruise sector workers for its 2024 overview of seafarer health. More than a third of the cargo ship workers who were on board when they completed the questionnaire had not had enough sleep in the previous 48 hours. Among cruise workers who were at sea, the figure was just under half. Seafarers attributed the shortfall to hours worked, work patterns, port duties, vessel movement and noise, all of which they reported as worse than in 2011 and 2016.

Professor Helen Sampson, who directs SIRC, put it this way: “Despite better monitoring of staff work/rest hours, fatigue remains an intractable problem for seafarers.”

The Seafarers Happiness Index for Q2 2026 recorded overall happiness at 6.87 out of 10, down from 7.18 the previous quarter. Workload management scored 6.20. The report describes a relentless cycle of 6-on/6-off watchkeeping, rapid port turnarounds, heavy paperwork and constant inspections.

The oldest figures still in circulation set a floor. A US Coast Guard study of 397 investigated casualties, published in 1996, found fatigue contributing to 16% of critical vessel casualties and 33% of personnel injury casualties. Those figures predate ECDIS, the MLC and the Manila Amendments, so treat them as a starting point.

How is marine fatigue managed on board?

Fatigue risk management systems are the direction of travel, and they run into real friction.

• Electronic rest hour logging makes recording easier without making the underlying workload smaller. The WMU found it can make record adjustment easier too.
• Bridge navigational watch alarm systems are mandated by SOLAS and are designed to escalate to the master if the watchkeeper stops responding. They only help when they are switched on, and casualty reports repeatedly find them off.
• Alarm burden works against the officer it is meant to protect. When a bridge generates more alerts than a person can act on, the rational response is to silence them, which is a safety risk in its own right.
• Manning levels sit underneath all of it. The MAIB documented two vessels of similar size, similar cargo and similar route, both under different flags, where one required a crew of seven and the other a crew of five. West of England’s loss prevention team has argued for a move from minimum manning to optimal manning.
• Training and awareness help crews recognize impairment in themselves and each other, which is one of the areas crew training programs can address directly.

None of this is quick. Cybersecurity, crew acceptance and compatibility with existing bridge equipment are ordinary obstacles to any change in how the watch is supported, and they deserve to be planned for rather than assumed away.

How Orca AI supports crews working under fatigue

The officer of the watch stays in command. What the platform adds is a second set of eyes that doesn’t get tired, and a record of the watch written by something other than the person standing it.

• Continuous detection through the night watch. SeaPod combines day and thermal cameras with mandatory ship sensors, including AIS, Radar, GPS, gyro, depth and wind. It detects, tracks and classifies targets, including vessels and objects that carry no AIS, and surfaces collision risk indicators such as CPA, TCPA, COG and SOG. Detection performance at 0400 is the same as at 1400.
• Earlier warning, so action can be taken in ample time. Surfacing a developing close encounter earlier gives a tired officer the one thing fatigue takes away first, which is time to think. That supports the situational awareness the watch depends on, and it works alongside Radar and ECDIS.
• An objective record of what happened on watch. FleetView records navigational events continuously and makes them reviewable ashore. Safety teams can see how encounters were handled across a fleet, which is a different kind of evidence from a rest hour log.
• Visibility for the master. MasterView brings the same event and risk picture to the master, scoped to their own vessel, so patterns in watch performance surface while the ship is still at sea.

Fatigue is a manning and scheduling problem. No camera fixes a 6-and-6 rotation. What technology can do is stop the consequences from arriving unannounced, and give shore teams something better than paperwork to look at.

For more on how this plays out across a fleet, read tackling crew fatigue, the maritime safety glossary entry, and our safety report with NorthStandard.