The Maritime Labour Convention sets minimum rest for seafarers in Standard A2.3, and almost every commercial vessel, including most professional yachts, lives under it through its flag state's law. The headline numbers are easy to recite. The days that get vessels into trouble are the borderline ones, where the outcome turns on subtleties the headline never mentions. This article covers both. It is not legal advice; your flag's marine notices and your management company carry the detail for your vessel.
The three rules
- At least 10 hours of rest in any 24-hour period.
- At least 77 hours of rest in any 7-day period.
- Rest may be divided into no more than two periods, one of which must be at least 6 hours long, and the interval between consecutive periods of rest must not exceed 14 hours.
Rest means time off duty. Short breaks inside a working stretch do not count: under MCA guidance a break has to reach one hour before it counts as rest at all. A 40-minute lunch between two working stretches is work, as the rules read it.
"Any 24-hour period" means rolling, not the calendar day
The rule does not say "each day". It says any 24-hour period, and that is a harder test: draw a 24-hour window starting at every point in the schedule, and the rest inside every one of those windows must reach 10 hours. A crew member can be comfortably rested on Monday and on Tuesday as calendar days, and still fail the window that runs from Monday noon to Tuesday noon, because a late finish and an early start landed in the same window. The 77-hour rule works the same way across any 7 days.
This is the single most common surprise in rest-hour compliance: tools and paper forms that only check calendar days will miss breaches the regulation defines, and a Port State Control officer is entitled to check the windows.
Extra rest counts toward the week
The two-period rule governs how the minimum 10 hours may be structured. It does not mean rest beyond those periods is ignored. MCA guidance (MSN 1877, Amendment 2) is explicit: additional rest periods of one hour or more, on top of the one or two periods making up the 10-hour minimum, count toward the weekly 77-hour total. A third rest block in the middle of a working day, if it is at least an hour long, is real rest in the weekly arithmetic. Some tools discard it and read stricter than the rules require; the regulation, and MCA's own words, say it counts.
Who the rules apply to
MLC applies to seafarers on commercially operated vessels, which for yachts generally means every crew member on a commercially registered yacht, with flag codes such as the Large Yacht Code applying the regime to the sector. Watchkeepers additionally sit under STCW's near-identical rest rules, which carry their own exception clauses; the differences are covered in STCW vs MLC rest hours.
The record is part of the rule
A2.3 also requires records of daily rest to be kept, in a standardised format, signed by the master or an authorised officer and by the seafarer, with the seafarer given a copy. The record, and what an inspection does with it, is its own subject: rest-hour records and inspections.
How The Muster App applies these rules: crew log their day on their own phone and the app checks it on the spot, offline included, against three named rules: the 10 hours in 24, the 77 hours in 7 days, and the two-period structure. The checks run over rolling windows, the way the rules are written, not calendar days; short breaks under an hour are not counted as rest; and additional rest of an hour or more counts toward the weekly total, per the MCA guidance above. When a day crosses a limit, the rule it crossed is named on the screen, and the day cannot be saved until a comment explains it. You can try the arithmetic yourself on the rest hours calculator.