Watch and Fatigue Management Explained

Prerequisites

You should already hold, or be at the standard of, RYA Coastal Skipper, and have experience of night passages as crew and as skipper. In particular you should know:

COLREGs Rules 5 (lookout), 7 (risk of collision), 8 (action to avoid collision) and 19 (restricted visibility), and the lights of power-driven vessels, sailing vessels, fishing vessels and vessels restricted in their ability to manoeuvre.
How to use radar and AIS at a basic level, including CPA and TCPA.
How to keep a deck log.

The Yachtmaster Offshore qualifying experience includes 2 overnight passages; you will be expected to describe how you organised watches on them.

Learning Objectives

Choose and design a watch system suited to crew numbers, experience and passage length (RYA syllabus: skippering, watchkeeping).
Explain how dog watches rotate the schedule.
Conduct a structured watch handover.
Explain how fatigue develops, recognise its signs (including microsleeps), and apply countermeasures.
Know the MCA/STCW minimum rest standards and apply them sensibly on recreational passages.
Keep a proper lookout by sight and hearing, integrating radar and AIS without relying on them.
Write standing orders and night orders.
Manage sleep in double-handed and single-handed sailing.
Explain the legal and practical duties of the skipper and the watchkeeper under COLREG Rule 5 and SOLAS Chapter V.
Plan crew welfare (food, hydration, warmth, sleep) and decide what to do when crew are lost to seasickness or injury.

These map to the RYA Yachtmaster Offshore syllabus topics "Watchkeeping and fatigue management" (watch systems, handover, fatigue recognition and mitigation, lookout including radar and AIS, standing orders) and "Skippering: crew management", and to the shorebased Offshore content on passage planning for crew rotation. They also underpin the Yachtmaster Ocean topic of extended crew management.

Exam-style tip: the Yachtmaster Offshore examiner will ask you to explain your watch system for an overnight passage with the crew you have, to justify it, and to describe what you would change if conditions deteriorated or two crew were seasick. Expect to produce a watch bill during the preparation week, to show your standing orders, and to be observed handing over. The strongest candidates show that they look after their own rest, and give a reason for every choice.

Why Watchkeeping Matters

Most offshore collisions and groundings involving yachts trace back to the same root causes: nobody was looking, or the person looking was too tired to understand what they saw. COLREG Rule 5 requires every vessel to "at all times maintain a proper look-out by sight and hearing as well as by all available means appropriate in the prevailing circumstances". The watch system is how a skipper meets that legal duty 24 hours a day while still giving the crew enough sleep to function.

Watchkeeping failures rarely happen suddenly. They develop slowly, as accumulated fatigue erodes alertness and judgement, until a ship is missed or a wind shift is not noticed.

Watch Systems

The right system depends on crew numbers and ability, the length of the passage and the expected conditions. Whatever the system, each watch should contain someone competent to handle the boat and make collision avoidance decisions, and the skipper must have protected rest.

Four on, four off

The traditional two-watch system splits the crew into two teams that alternate four-hour watches: six watches in 24 hours.

Advantages: simple, predictable, and each watch has several people. Disadvantages: the maximum unbroken sleep is about three and a half hours once you allow for handover, getting undressed and dressed; and with six watches, the same team gets the same night watches every night.

Dog watches

To rotate the schedule, the 1600 to 2000 watch is split into two two-hour "dog watches". This gives seven watches per day, an odd number, so each team's watch times shift by one slot each day.

The dog watches also fall conveniently around the evening meal, so both watches can eat together.

Three-watch systems

With six or more crew, three watches of two, each standing four hours on and eight hours off, give much better rest. With a crew of three, a three-watch system of single watchkeepers can work in benign conditions with a good autopilot, but the lone watchkeeper must be able to call for help instantly and must not leave the cockpit without someone awake.

Three-watch system: four hours on, eight hours off, rotating A, B, C

Variations include shorter night watches (three hours on, six off) when it is cold or rough, and longer day watches when it is pleasant. Some skippers use a "Swedish" system with five watches a day of unequal lengths to rotate the schedule.

Choosing a system

Crew	Typical system	Notes
2	Alternating watches with timer naps	See double-handed section; very tiring
3	3 hours on, 6 off (single watchkeepers)	Skipper often floats; needs good autopilot
4	4 on, 4 off in pairs, or 3 hours on, 6 off singles with skipper floating	Pairs give mutual support
6 or more	4 on, 8 off in threes, or 4 on, 4 off with dog watches	Spare hands for sail changes

The skipper may stand a watch or float. A floating skipper is free to navigate, plan and respond to calls, but must still schedule real sleep. A tired skipper making a critical decision is a hazard.

Worked example: sleep arithmetic for a four-on, four-off watch

A crew member on a strict four-on, four-off system is on watch 0000 to 0400, 0800 to 1200 and 1600 to 2000. Realistic sleep per off period, allowing 30 minutes to hand over, change and eat, and 15 minutes to wake and dress:

Off period	Length	Realistic sleep
0400 to 0800	4 h	about 3 h
1200 to 1600	4 h	about 3 h (daytime sleep is lighter)
2000 to 0000	4 h	about 3 h (but difficult to fall asleep early in the evening)

That is about 9 hours of fragmented sleep in 24 at the very best, and the longest unbroken period is about 3 hours. After three or four days the sleep debt is real. Compare a three-watch system of four on and eight off, where each person gets at least one long block of about 7 hours of sleep. For the same crew size you may be able to achieve this only with six or more people; with fewer, you need to shorten watches, float the skipper, or accept that passages longer than two days will be tiring.

Watch Handover

The incoming watch arrives on deck from a warm bunk with no situational awareness, eyes not yet adjusted to the dark. The handover is when information is most easily lost. Use a fixed checklist so nothing is omitted, and keep it to three to five minutes.

Position: latest fix or EP, how it was obtained, and how confident it is.
Course and trim: course being steered, autopilot setting, sail plan, any reefs.
Weather: wind trend, barometer reading and tendency, visibility, anything forecast in this watch.
Traffic: every contact by eye, radar and AIS, with bearing, range, CPA and TCPA and whether the bearing is changing.
Standing orders: any special instructions from the skipper, including when to call.
Equipment: anything behaving oddly, such as a navigation light, autopilot wandering, engine temperature, bilge pump cycling.
Next waypoint or hazard: what is coming up and when; any alteration due.
Crew below: who is sleeping, anyone seasick or unwell.

Good practice:

The incoming watch comes up five to ten minutes early, puts on lifejacket and tether below, and lets their eyes adapt to the dark before taking over.
The outgoing watch does not leave until the incoming watch says, "I have the watch", after confirming they have seen each contact.
Do not hand over in the middle of a collision avoidance manoeuvre or sail change; finish it first.
Log the handover.

Fatigue

Fatigue is the silent killer offshore. It degrades every skill a watchkeeper needs: perception, attention, memory, reaction time and judgement. Its worst feature is that the tired person is the least able to recognise how impaired they are.

How fatigue builds

Alertness falls with time awake and with sleep debt accumulated over several days. After about 17 to 19 hours awake, performance is similar to having a blood alcohol level of 0.05%; after 24 hours it is comparable to 0.1%, above the UK drink-drive limit.

Alertness declining with hours awake through impaired judgement to microsleeps

The circadian low

The body clock adds a daily cycle. Alertness is lowest, and the risk of error highest, between about 0200 and 0500, when core body temperature is lowest. There is a smaller dip in the early afternoon.

Circadian rhythm with the danger zone from 0200 to 0500

Put the most experienced watchkeepers on watch through the small hours when possible, keep night watches shorter in hard conditions, and expect the first night at sea (before the crew has adjusted) to be the hardest.

Microsleeps

A microsleep is an involuntary lapse of a few seconds during which the brain stops processing what the eyes see, even though the eyes may be open. The sufferer is often unaware it happened.

Microsleep episodes: eyes open, brain offline for two to five seconds

At 6 knots a yacht travels about 15m in a 5-second microsleep; a ship at 20 knots closing head-on covers about 70m in the same time. A watchkeeper who suffers repeated microsleeps can miss a ship's lights changing aspect entirely.

Warning signs

Heavy eyelids, frequent yawning, rubbing eyes.
Irritability, apathy, loss of humour.
Fixation on unimportant details while missing important ones.
Missed radio calls; slow responses to questions.
Poor helming: wandering course, gybes, sails flapping.
Forgetting what you just checked.
Seeing things that are not there (hallucinations occur with severe sleep deprivation, especially in single-handed sailing).

Countermeasures

Before departure:

Bank sleep: arrive at the boat well rested; avoid a late night before an early departure.
Plan the watch system so everyone gets protected sleep from the first night.

At sea:

Sleep hygiene: dark, ventilated, quiet berths with lee cloths; earplugs and eye masks; sleep whenever off watch, even in the day.
Food and drink: regular hot meals with complex carbohydrates and protein; avoid relying on sugar. Enforce hydration: mild dehydration mimics fatigue and worsens seasickness.
Warmth: cold accelerates fatigue. Dress for the watch, including a warm layer you can add.
Activity: change tasks on watch, take turns on the helm, stand up and move.
Shorter watches in heavy weather or cold.
Seasickness management: seasick crew become fatigued very quickly. Treat early and rest them.

Sleep inertia, napping and sleep debt

Waking from deep sleep leaves a period of sleep inertia lasting 5 to 20 minutes, sometimes more, when thinking is poor. A person woken suddenly in the middle of a sleep cycle may be disoriented. Practical implications:

Wake the incoming watch early enough (10 to 15 minutes before handover) so that inertia has passed before they take responsibility for the boat.
Do not wake a crew member and send them straight to the helm in a difficult situation unless there is no alternative.
A nap of about 20 minutes refreshes without deep sleep; a nap of 90 minutes covers a full sleep cycle and is more restorative. Naps of 30 to 60 minutes risk waking from deep sleep and bring the worst inertia.
Sleep debt accumulates. If you lose two hours of sleep each night for four nights you have lost eight hours, and it takes several nights of full sleep to recover. Short rest can improve alertness for a few hours but does not clear the debt.
Banking extra sleep before a passage helps a little, but cannot be stored indefinitely.

The skipper should keep a simple record of when each person last had a block of sleep of at least four hours. A crew member who has had none in 18 hours is a risk.

Caffeine

Caffeine is a useful tactical tool but a poor strategy. It takes about 20 to 30 minutes to work, peaks at about an hour, and has a half-life of around 5 hours, so a coffee before going off watch can stop you sleeping.

Use it before a known difficult watch, such as the 0200 to 0400, or before a demanding landfall. Do not use it to replace sleep; heavy regular use leads to dependence, reduced effect and withdrawal headaches when supplies run short.

Crew Welfare Offshore

Fatigue is not only about sleep. Food, water, warmth and morale all change how well people stay alert.

Food. Plan menus before departure. Most crew eat less when seasick or tired, so provide small, frequent portions, plain carbohydrates, and warm food at the start and end of night watches. A mother watch or designated cook who is off the watch rota for part of the day makes this easier.
Hydration. About 2 to 3 litres per person per day in temperate conditions, more in heat. Dehydration looks like tiredness: headache, poor concentration, dark urine.
Warmth. A cold crew member burns energy and loses attention. Check clothing before the first night. Offer dry spare layers. Do not allow anyone to stay on deck beyond their watch if they are shivering.
Seasickness. Encourage prevention before sailing, and treat quickly. A seasick crew member loses sleep, water and food and becomes fatigued within a day.
Morale. Recognise good work, share jobs fairly, rotate unpopular tasks, and mark the passage milestones. Poor morale leads to disputes over watches and rest.

Rest Hour Standards

The MCA applies the STCW and Maritime Labour Convention rest hour rules to commercially operated vessels. A Yachtmaster with a commercial endorsement must know them.

MCA/STCW minimum rest hours: 10 in any 24, at most two periods, one of at least 6 hours, 77 in 7 days

At least 10 hours of rest in any 24-hour period.
At least 77 hours in any 7-day period.
Rest may be split into no more than two periods, one of which must be at least 6 hours.
Intervals between rest periods must not exceed 14 hours.
Records of hours of rest must be kept.

A strict four-on, four-off gives 12 hours off in 24 but in three separate blocks, none longer than four hours, so it does not meet the STCW pattern. Recreational skippers are not legally bound by these rules, but they are an excellent benchmark: if your watch system cannot come close, your crew will accumulate sleep debt over a multi-day passage. Watch systems with a longer off period (for example a six-hour daytime off watch) help.

Lookout

Systematic scanning

Casual glances around the horizon miss things. Train every watchkeeper to scan systematically.

Near water: debris, fishing floats, other boats close by, and the boat itself (sails, chafe, crew).
Horizon sweep: in overlapping sectors of about 10 to 15 degrees, pausing on each, because the eye detects objects better when still. Look all the way round, including behind the sails and the headsail blind spot (look under the genoa).
Instruments: compass course, wind speed and direction, depth, boat speed.
Radar and AIS: correlate every contact with what you can see.
Repeat every three to five minutes.

At night, protect night vision: red lights only in the cockpit and at the chart table, screens dimmed to night mode. Full night vision takes 20 to 30 minutes to develop and is lost in seconds with white light. When taking a bearing of a light, use a hand-bearing compass and note whether the bearing is changing over a few minutes; a steady bearing with decreasing range means risk of collision (Rule 7).

Integrating radar and AIS

Electronics extend the lookout but never replace it.

What radar and AIS show compared with what they miss

AIS shows vessels that transmit: all ships over 300gt on international voyages, passenger vessels, and many fishing vessels and yachts. It does not show small fishing boats, many yachts, or anything with a switched-off transponder. AIS data can also be wrong (incorrect heading, stale position).
Radar detects targets that reflect. Steel ships show well; GRP yachts, wooden fishing boats and kayaks may be lost in sea clutter or rain clutter, especially close in.
Visual lookout catches what both miss, and gives aspect from a vessel's lights.

The correct approach is to correlate every visual contact with a radar return and, where it exists, an AIS target, and to treat any contact you cannot see but which shows on radar (or vice versa) as needing extra attention. Use AIS CPA alarms and radar guard zones as an extra safety net, never as the lookout.

Standing Orders and Night Orders

The skipper's standing orders are written instructions for every watch for the whole passage. Night orders are added each evening for the specific night ahead. They tell the watch what to do and, critically, when to call the skipper. A typical set:

Call the skipper immediately if:

Any vessel will pass within 1nm, or if in any doubt about another vessel's intentions.
The wind exceeds 20 knots apparent, or shifts by more than 30 degrees.
The barometer falls more than 2 hPa in an hour.
Visibility drops below 2nm.
You are unsure of the position, or a light or mark expected is not sighted on time.
Any equipment fails or anything unusual happens.
You feel too tired to keep a proper watch.

Other standing orders: lifejackets and tethers on deck at night and in Force 5 or above; nobody goes forward at night without telling someone and clipping on; log entries every hour. Every watchkeeper should read and sign the orders.

The last item, "call me if you feel too tired", is important. It tells the crew that admitting fatigue is professional, not weak.

A template for night orders

Many skippers leave a short written note in the log for each night. A suitable template:

Date and time written: and the skipper's name.
Course and intended track for the night, with expected waypoints and times.
Expected hazards: lights to expect and the time you should see them; shipping lanes or fishing fleets; tidal streams and their times.
Weather: the forecast for the night and what would trigger a reef or a change of course.
Calling criteria in addition to the standing orders: for example, "call me at 0100 or sooner if the lighthouse is not seen by 0030".
Engine, battery, and fuel notes.
Signature of the watch leaders acknowledging that they have read the orders.

Review night orders after each night: remove those that were never useful, and add those that would have helped.

Log Keeping on Watch

The deck log is a legal record. Each watch records, at least hourly: time, position (and how obtained), course steered, log reading, speed, wind direction and force, sea state, barometer, visibility, sail plan, engine hours, and remarks (traffic, events, changes). Entries should be contemporaneous and factual. Mistakes are struck through with a single line and initialled, never erased.

Double-Handed and Single-Handed Watchkeeping

With two people, continuous full watches are impossible for long. With one, there is no watch at all when the sailor sleeps. Both situations involve a conscious acceptance of risk, and Rule 5 still applies.

Double-handed

Common approaches:

Alternate watches of two or three hours by night, with the off-watch person sleeping fully, and longer, flexible watches by day.
In busy waters, the person on watch stays awake; in open ocean, the watchkeeper may take short timed naps of around 20 minutes, waking to a loud alarm, scanning the full horizon and checking instruments before resetting.
Use AIS CPA alarms, radar guard zones and the autopilot as safety nets.

A 20-minute interval is used because a ship at 20 knots appearing on the horizon about 6 to 8nm away will take roughly 20 minutes to reach you.

Single-handed

Solo sleep management: scan, set alarms, sleep 15 to 30 minutes, repeat

Single-handers use polyphasic sleep: many short naps of 15 to 30 minutes, totalling perhaps 5 to 6 hours a day. Before each nap: a full 360 degree scan, radar check, AIS alarm set, course safe and sails set conservatively. Single-handers plan routes to cross shipping lanes and approach coasts while awake, and sleep only in open water.

Emergencies and Calling All Hands

A watch system works for steady conditions. In an emergency, such as a gale, a collision risk, a fire or a person overboard, the skipper calls all hands. Some principles:

Call early. It is better to wake the off watch for a reef that was not strictly needed than to struggle short-handed.
Brief quickly. Tell the crew what the problem is, who does what, and how long it should last.
Re-establish the watch system as soon as possible. After the emergency, send the tired crew to bed, and get the skipper to rest. A crew that stays up for 24 hours after an incident is the next incident.
Log it. Record the event, the decisions and the times.

For a man overboard, the watchkeeper shouts, points, throws the lifebuoy and danbuoy, presses the MOB button on the GPS and starts the engine as the skipper directs. Practise this at night as well as by day, because the watch on deck at 0300 may be one or two people. Wear a lifejacket with a light and, ideally, a personal AIS beacon or PLB at night.

Worked Example: Watch Bill for a 48-Hour Passage

Crew: skipper (Yachtmaster), Anna (Coastal Skipper), Ben (Day Skipper), Chris (Competent Crew, first offshore passage). Passage 48 hours, departure 0800.

Decision. Two watches, four on and four off with dog watches. Because the skipper wants to float, only three people are available for two watches, so the skipper fills the gap at night:

Watch A: Anna (watch leader) and Chris, so the least experienced crew member is always paired with the strongest watch leader.
Watch B: Ben alone by day, with the skipper on call; Ben plus the skipper by night, so there are always two on deck in darkness.
The skipper sleeps during Watch A's night watches, protected unless called under the standing orders, and catches up during Watch A's daytime watches.

Schedule (day 1): A 0800 to 1200, B 1200 to 1600, A 1600 to 1800 (first dog), B 1800 to 2000 (second dog), A 2000 to 2400, B 0000 to 0400, A 0400 to 0800. The next day the pattern shifts, so A takes the 0000 to 0400.

Briefing. Standing orders read and signed. Handover checklist pinned by the companionway. Night orders written each evening. Chris is told explicitly that calling the skipper is always correct.

Worked Example: Two Crew Down

Hour 36 of a 60-hour passage. Two of four crew are badly seasick and cannot stand a watch. You and the other fit crew member have been standing six on, six off for 24 hours. You are 40nm from the destination, approaching a busy shipping lane, and you notice that you are making simple errors.

Assessment. Lookout is impaired; you are effectively double-handed and fatigued; the area ahead is high-risk.

Options. Heave-to clear of the lane and rest in turns, crossing in daylight; divert to a closer port if one exists; inform the Coastguard of your situation and intentions; continue with all alarms set, accepting high risk. The safest is to stop clear of the traffic, sleep in short shifts, rehydrate the sick crew, and cross the lane when rested and in daylight. Log the decision and the reasoning.

Worked Example: Rest-Hour Audit

Over 24 hours a crew member's log shows: on watch 0000 to 0400, off 0400 to 0800 (slept 3 hours), on watch 0800 to 1200, off 1200 to 1600 (slept 2.5 hours), on watch 1600 to 1800, off 1800 to 2000 (ate and cooked, slept 0), on watch 2000 to 2400.

Rest hours in 24: 4 + 4 + 2 = 10 hours of off-watch time, so on paper the 10-hour minimum is just met. But it is in three periods, none of them 6 hours, so the rule of no more than two periods with one at least 6 hours is not met.
Actual sleep: 3 + 2.5 + 0 = 5.5 hours.
Conclusion: the person is about 2.5 hours a day short against a typical need of 8 hours. After four days they are 10 hours down. The skipper should lengthen the off-watch periods, lighten the duties (the cook should not also stand a watch), or add a crew member.

An examiner will be impressed by a candidate who can do this arithmetic on the spot and propose a fix.

Sleep Science and Fatigue Risk Management

Sleep stages and why interrupted sleep is poor sleep

Sleep runs in cycles of roughly 90 minutes, passing through light sleep, deep (slow-wave) sleep and REM sleep. Deep sleep dominates the first half of the night, REM the second half. Because four-hour rest blocks are broken by the need to get up for the next watch, a sailor often misses the longer cycles. A minimum useful block is about 90 minutes (one cycle), and a block of at least four hours is needed to let deep sleep consolidate. Two blocks of four hours (four-on, four-off) are workable; a pattern of 90-minute fragments is not, so avoid it unless the crew is small.

Sleep debt arithmetic

Most adults need 7 to 8 hours in 24. A watchkeeper who gets 5 hours a day builds a debt of 2 to 3 hours a day. After four days the cumulative deficit is about 10 hours, roughly equivalent to missing a full night, and performance deteriorates to a level comparable with a blood alcohol level of 0.05 percent. After 17 to 19 hours awake the effect on reaction times is similar to 0.05 percent, and after 24 hours awake to about 0.10 percent, which is above the UK drink-drive limit. This is the physiological reason for the limits on hours of rest.

Worked example: a rest-hour calculation

A crew member works the following in a 24-hour period: watch 0000 to 0400, rest 0400 to 0800, watch 0800 to 1200 (with an extra two hours on the sail change from 1200 to 1400), rest 1400 to 1600, watch 1600 to 2000, rest 2000 to 2400.

Rest periods: 0400-0800 (4 hours), 1400-1600 (2 hours), 2000-2400 (4 hours). Total = 10 hours.
Number of periods: three, which exceeds the limit of two.
The longest period is 4 hours, below the required 6 hours.

Although the total reaches 10 hours, the pattern breaches both the maximum of two rest periods and the minimum six-hour period. The fix: remove the 1400 extension, combine the rest into 1200 to 1600 and 2000 to 2400 with a watch swap so that one block reaches six hours, or have another crew member take the sail change.

Fatigue risk management as a system

Treat fatigue like any other hazard: identify, assess, control, review. Identification: pattern of watches, passage length, weather, experience, seasickness, stress. Assessment: use a simple traffic-light score at each handover (green rested, amber tired, red unfit). Controls: schedule, napping, stimulating tasks, double watch in the circadian low, reduced sail in the evening before fatigue builds, a decision to heave to or enter port when two or more crew are red. Review: record hours in the log and adjust each day.

Fatigue and seasickness

Seasickness and fatigue combine. Vomiting dehydrates; the sick crew member cannot eat or sleep, and may be fit for no useful watch for 24 to 48 hours. Anti-emetics such as hyoscine can cause drowsiness, so the helmsman should not take them without checking the effect during daylight first. Start medication before sailing, not after the first symptoms. Keep the seasick person warm and fed with small amounts of dry food, and put them on a shorter, simpler watch such as lookout in the cockpit with a bucket rather than at the chart table.

Cold, heat and nutrition

Core temperature affects alertness. A cold crew member loses dexterity and concentration quickly, and hypothermia begins below 35 degrees C core temperature. In hot sun, dehydration of only 2 percent of body weight impairs concentration. Plan: 2 to 3 litres of fluid per person per day offshore, a hot meal every 6 to 8 hours, simple snacks that can be eaten with one hand, and regular drinks on every watch change. Alcohol is excluded at sea, because it degrades sleep quality as well as judgement.

Fatigue indicators the skipper should watch for in others

Watch for slowed speech, repetition of the same question, failure to log or plot, poor mood, clumsiness, delays in responding to a call, skipped meals, and a crew member who denies being tired. People are poor judges of their own fatigue. Make a rule that the watch leader or the skipper may stand down anyone who shows two or more indicators, without argument.

Common Mistakes

Unstructured handovers. Use a written checklist; do not leave until the new watch confirms they have seen each contact.
Relying on AIS and alarms. Rule 5 requires a lookout by sight and hearing.
Skipper never sleeping. A fatigued skipper makes poor decisions; delegate and schedule rest.
Same people always on the 0000 to 0400. Use dog watches or another rotating system.
Ignoring early fatigue signs. Treat irritability and poor helming as signals to act.
Caffeine instead of sleep. Use it tactically only.
White light in the cockpit at night. It destroys night vision for 20 minutes.
Not looking under the genoa. A large blind spot exists on the lee bow.
Waking a crew member and expecting instant performance. Allow time for sleep inertia.
Ignoring welfare. Cold, hungry, thirsty crew fatigue faster. Plan meals and warm clothing.
Weak night orders. Orders that do not say when to call, or are not signed, leave the watch guessing.

Summary

The watch system is how the skipper meets Rule 5 while letting the crew sleep.
Choose the system by crew number and experience; dog watches rotate a two-watch system.
Use an eight-point handover checklist: position, course and trim, weather, traffic, orders, equipment, next waypoint, crew.
Fatigue builds with time awake and sleep debt; alertness is lowest from 0200 to 0500; microsleeps occur without the sufferer knowing.
STCW/MCA: 10 hours rest in 24, 77 in 7 days, at most two periods with one at least 6 hours.
Scan systematically every three to five minutes, preserve night vision, and correlate visual, radar and AIS.
Standing and night orders tell the watch when to call the skipper.
Double-handed and solo sailors accept extra risk and manage it with timed naps, alarms and route choice.

Check Your Understanding

1. Why are dog watches used in a four-on, four-off system?

Answer: Splitting 1600 to 2000 into two two-hour watches gives seven watches a day, an odd number, so each team's watch times shift daily and the same people do not always stand the 0000 to 0400.

2. List the eight items in a watch handover.

Answer: Position, course and trim, weather trend, traffic contacts with CPA and TCPA, standing orders, equipment status, next waypoint or hazard, and status of the crew below.

3. When is a watchkeeper's alertness typically lowest, and how should the skipper plan for it?

Answer: Between about 0200 and 0500. Put experienced watchkeepers on then, keep night watches shorter in hard conditions, and use caffeine tactically before those watches.

4. What is a microsleep and why is it particularly dangerous?

Answer: An involuntary lapse of a few seconds in which the brain stops processing visual information, even with eyes open. The sufferer is often unaware it happened, so they do not know they have missed something.

5. Does a four-on, four-off system meet STCW rest-hour requirements? Explain.

Answer: No. Although it gives 12 hours off in 24, it is split into three periods none of which is 6 hours long. STCW requires at least 10 hours rest in 24 in no more than two periods, one at least 6 hours.

6. Why can a small wooden fishing boat be missed by both radar and AIS?

Answer: It probably carries no AIS transponder, and wood or GRP gives a weak radar echo that can be lost in sea or rain clutter, especially close in. Only a visual lookout reliably detects it.

7. Give five situations in which standing orders should require the watch to call the skipper.

Answer: Any vessel passing within 1nm or of doubtful intentions; wind above a set threshold or a big wind shift; barometer falling fast; visibility below 2nm; doubt about position or a light not sighted when expected; any equipment failure; the watchkeeper feeling too tired.

8. Why do double-handed sailors often use a 20-minute nap interval?

Answer: A fast ship appearing over the horizon at about 6 to 8nm can reach the yacht in about 20 minutes, so waking every 20 minutes to scan gives a chance of seeing it before it is too close.

9. How should caffeine be used on a long passage?

Answer: Tactically, before a difficult watch or landfall, allowing 20 to 30 minutes for it to act, and not shortly before going off watch to sleep. It should not replace sleep, and heavy use leads to dependence and withdrawal.

10. A crew member has slept three hours in the last 24 and is cold and quiet. What should the skipper do?

Answer: Treat it as a fatigue and possible hypothermia concern: bring them below, warm and feed them, let them sleep, adjust the rota and take their duties. Log the decision. Do not wait for them to complain, because tired people rarely notice their own impairment.

11. What is sleep inertia and how does it affect the handover?

Answer: A period of reduced alertness and poor thinking lasting 5 to 20 minutes after waking, especially from deep sleep. Wake the incoming watch 10 to 15 minutes early so that they are alert at handover, and do not hand over responsibility to someone who is still groggy.

12. A skipper in the cockpit at 0300 sees a ship's lights on AIS but cannot see them. What should be done?

Answer: Treat it as a real contact and check radar and the horizon in the direction of the bearing. Take a bearing if visible, assess CPA and TCPA, and call the skipper if the standing orders require it. Do not assume that AIS is accurate, and do not assume that the ship has seen you.