Sleep matters - how to cope when short-handed
Psychologist Chris Sharpley delves into the latest research on sleep and the lessons it holds for the cruising yachtsman or woman.
We spend about one-third of our lives sleeping and about one-quarter of that time dreaming. Lack of sleep can affect our ability to do many of the tasks involved in cruising, from concentrating on a navigation problem to just being civil to our crew or skipper.
Although the record of going without sleep is 11 days, the 17-year-old student who did that without drugs (even caffeine) became irritable, nauseous, had trouble recalling things and experienced delusions. Of interest, all these symptoms disappeared after the first sleep he had and there were no lasting harmful effects.
What is sleep?
The medical textbooks define sleep as "unconsciousness from which a person can be wakened relatively easily". People differ in terms of wakefulness, with some sleeping very soundly and requiring "a bomb" to wake them, while others wake at the slightest noise or change in their environment (eg, heeling to a breeze shift). We sleep in "stages" of about 1.5 hours, possibly waking for a few minutes between these stages.
What happens when we sleep?
When allowed to sleep without interruption, most people experience two types of sleep.
The first is called "slow-wave sleep" because the electrical activity of the brain takes the form of strong low frequency waves. Slow-wave sleep is very deep, restful and occupies most of our sleeping time (about 75 percent of the sleeping time of young adults). It's particularly dominant during the first hour or so after going to sleep. Blood pressure, breathing, and temperature slow down as much as 30 percent during slow-wave sleep. We tend not to move much during slow-wave sleep, and then only to adjust our position. If you have been awake for more than 24 hours, then this is the kind of sleep that you will experience in the first hour or so when you (finally!) go to bed. It's very refreshing and you may even wake from slow-wave sleep after about 90 minutes or so and feel ready to get up and start the day.
The second type of sleep is called "rapid eye movement sleep" or REM sleep, because our eyes move quickly when we are in this type of sleep. Occupying about one-quarter of our total sleeping time, REM sleep occurs about every 90 minutes for between 5 and 30 minutes. It's not as restful as slow-wave sleep and often includes vivid dreams and sometimes active body movements. Brain activity increases by up to 20 percent and includes more of the high-frequency waves that are associated with thought when we are awake.
As might be expected, the ratio of slow-wave sleep to REM sleep changes during the night as we become more rested. When we first go to sleep, slow-wave sleep takes up most of the time, with only short bursts of REM sleep. As we become more refreshed, REM sleep becomes more common. These two kinds of sleep cycle alternatively throughout our sleeping period
Brain waves, sleep and recuperation
It has been suggested that the main reason we need to sleep is to refresh our brains, which are composed of billions of nerve cells called neurons, joined together in various networks that allow signals to move from one part of the brain to another. Each neuron works by becoming charged with a small electrical current and then transmitting this current to adjoining neurons. Because it's so active, the brain uses about 15 times more oxygen than other parts of the body and also consumes a lot of energy. This is part of the reason why you may not be able to think so well when you are very hungry. It also means that prolonged wakefulness (such as an overnighter) will mean we have to eat more food to "top up" the energy sources stored in our cells.
The small electrical currents in our brains occur in waves, which can be classified according to their frequency in Hertz. When we are in slow-wave sleep, we experience delta waves (less than 3.5 Hz) that are of relatively high voltage. The next relevant waves are alpha waves (about 8 to 13 Hz), and these are associated with deep relaxation. Some forms of meditation produce alpha waves, giving a restful feeling that is very enjoyable and can leave us mentally and physically refreshed. When we are awake and concentrating on something, we produce beta waves. These vary in their frequency, ranging from 14 Hz to as high as 80Hz when we are really concentrating (eg, how strong is the tide and how far off is that sandbank?).
How much sleep do you need?
While this varies between people and according to age, most people need about 5 to 10 hours per night, the average being 7.5 hours. Teenagers' sleep requirements don't change when puberty strikes but the time at which teenagers can fall asleep does change. They find it more difficult to fall asleep early and to wake early, resulting in many young people being chronically sleep-deprived. If we think of how kindly we feel about the world when we haven't had enough sleep for several nights, we can better understand the attitudes and behaviour of teenagers early in the morning.
Older adults appear to require less sleep, but this can vary according to their levels of exertion and health. It's important to remember that the best indicator of how much sleep we need is how we feel and function during the day. If we feel alert and can solve problems and get along with others easily, then that's the sign that we have had enough sleep. If we feel sluggish, can't quite focus upon the problem at hand or think that the world is out to annoy us, then we probably need to consider getting a bit more sleep.
Sleep problems and disorders
Slow-wave sleep is usually deep and restful. However, sometimes people will become active during the final part of a slow-wave sleep period. They may speak (usually not intelligibly), move about, walk, scream or become distressed. It's best not to try to wake these people but simply lead them back to bed. Most times they won't remember anything about their experience in the morning. Children have sleep terrors and nightmares, the former usually passing with age, but we all sometimes experience the latter throughout our lives.
Perhaps one of the most common sleep complaints is waking up and remaining awake during the early hours of the morning. This can be distressing for a number of reasons, including the anxiety that we won't get back to sleep again before a demanding day, that we feel tired and need a rest, and that the time we have woken up is a bit unearthly (between 1-4am). This is the time that the body's circadian rhythms are at their lowest, and we will consequently feel worst Ð it's not all in your head.
Some people also have difficulty falling asleep, and that is usually due to either diet or worry. Some tips for getting to sleep are provided in the breakout box "Some steps towards a good night's rest."
Others suffer from more serious sleep problems and may have a sleep disorder. These can include sleeping too little, sleeping too much, not being able to stay awake and disturbances during sleep.
What can we do to maximise our chances of sleeping well?
There are several practical steps we can take to sleep better, get a good rest and not feel too bad about losing sleep. The essence of all those suggestions is to treat sleep like other aspects of your life. True, you will feel less than 100 percent when you sleep poorly, but you will survive a few nights' poor sleeping.
Particular demands of sleeping at sea
Not only is our bed moving through several dimensions quite quickly - thus making it difficult to remain still while asleep on board during a passageway - the noise of the boat's progress and the demands of watchkeeping can make complete rest hard to get. The subject of watchkeeping is large and complex but one aspect of it that is relevant here is the broken nature of our rest when at sea.
Several research studies have shown negative effects from broken sleep, mainly by reducing the level of alertness of watchkeepers. The National Transportation Safety Board 1990 report into the Exxon Valdez disaster of 1989 concluded that fatigue experienced by the watchkeeper (who had between 5 and 6 hours sleep split between afternoon and early morning) contributed to errors in navigation and the subsequent grounding of the ship.
The longer the better
The second major finding that emerges from the research literature is that one longer sleep per day is better than several shorter sleeps. This is based upon reports from the sailors themselves who were on watch as well as evaluations of their level of alertness. The most common watch schedule on the ships that were studied was the 4-on, 8-off, which resulted in "critical" fatigue levels in watch-keepers as much as 24 percent of the time because there was insufficient time to eat, relax and then sleep for about 7-8 hours uninterrupted.
It appears that having 5 to 6 hours sleep induces fatigue and reduced alertness in the average person, whereas having 7 to 8 hours uninterrupted sleep reduces fatigue and increases alertness. This critical (but average) figure of 7 to 8 hours uninterrupted may be quite difficult to achieve when there are only two people onboard (and may explain why so many couples sail only relatively few days per week). If you fit this category, then there is some good news from one study that showed that a nap of about 20 minutes taken between six and ten hours after waking was able to partially compensate for the fatigue and alertness problems associated with restricting sleep to only four hours.
Suggestions for sleeping (and resting) at sea
One of our breakout boxes shows some of the possible ways the research findings could be incorporated into a tyHow particular crews handle the interrupted nature of sleep at sea is largely an individual matter. For instance, some of us like to sleep early in the evening, some like to be awake at midnight and some relish the early hours of the morning in bed. It's vital that your crew discusses each individual's preferences to see if there is any reciprocal arrangement that can be made. If your crew is composed of a mix of age groups, older persons may prefer to sleep between late afternoon and midnight, whereas the younger crew members will probably find it easier to stay awake for that period and go to bed later and rise later. Older people are generally more alert in the morning and sleepier in the evening.
Stick to it
If there are immediately obvious reciprocal arrangements that come to mind after discussions of sleep preferences, then try these first. If no such arrangements are obvious, working out a schedule can help reduce the discomfort of waking when we really wish to sleep. Then, when each member of the crew has a designated sleep/wake pattern, stick to it. Research on shift workers has repeatedly shown that the most stress comes from changes in shifts. So, if you elect (or are given) the graveyard shift, keep it. As you become used to it, you will also manage the initial discomfort more effectively, maybe even eliminating it. Rotating shifts daily or weekly can prevent people adjusting to a sleep-wake pattern and this in turn increases the demands and damage upon the body (and decision-making ability).
However, even more important than this is the assurance that each person has a chance to get the kind of sleep that is needed for full brain recovery when off-watch. The critical factor appears to be the chance of getting a complete sleep of about 7 to 8 hours at a time on average. This may suggest that, even where short-handed, longer shifts may enable people off-watch to recover by being able to sleep for the length of time they need to recover their brain capacity. While this may initially appear to be tough on the watch-keeper who is awake, it appears not to be as harmful to alertness as shorter shifts, which also only allow shorter sleep periods. And, there is the thought of that lovely uninterrupted period relaxing and sleeping after completing the watch!
Your own boat
I must emphasise that the ideas reported here are based upon research literature. Quite obviously no one is an expert on what works best for everyone else. If you have developed a system that works in terms of reducing fatigue, maintaining alertness and can do so without hiring a crew of 20, then go with your own discoveries.
Chris Sharpley is a retired Professor of Psychology and now sails his Endurance 35 (Panacea) along the Queensland coast between various consulting and research jobs. He tries not to sail overnight if he can help it.
some steps towards a good night's rest.
HAVE A PLACE TO SLEEP
Identify a bunk, bed, floor or whatever place you are going to sleep in; then use it regularly so that it becomes associated with rest!
MAKE IT COMFORTABLE
Try to avoid making your bed in the cockpit. Chances are you will be disturbed. Similarly, if the engine is on or other noise bothers you, think of earplugs. Be warm and have a comfy mattress.
WATCH YOUR DIET
If you want to relax, don't set your body up to race. Caffeine, high sugar content, heavy food all set your body on high. If you're hungry when going to bed, then have a very light snack. Alcohol will certainly put you to sleep if you have enough of it, but you won't get much value from the sleep you have, quite apart from the hangover when you wake up.
HAVE A TIME TO SLEEP
Try to find the right time for you to go to sleep. Many people experience a "sleep window", when they feel drowsy and will fall asleep easily. The physical and psychological health benefits of naps are well established.
SET YOURSELF TO REST
Try some deep breathing, muscle relaxation, mental relaxation, even counting sheep Ð whatever works for you.
If there's something on your mind, write it down, then leave the problem for when you get up.
TRY REST INSTEAD
Even if you don't sleep well, you can get some valuable mental rest. Various kinds of meditation slow the body down. Closing the eyes increases alpha wave activity. Deep breathing can produce a feeling of relaxation and refreshment. Simply remaining still for a reasonable period of time can also reduce the anxiety and fretfulness we experience when missing sleep.
DON'T WORRY ABOUT IT
Accept that sometimes most of us will sleep poorly. It's not a major health problem and we can usually get a good sleep in the next few days.
If nothing serves to get you to sleep, discuss this with your GP.
balancing the workload at sea
ACCEPT THE 7-8-HOUR RULE
While that's an average, it's fairly certain that most of us need that amount of sleep to function at our best. We can all do with less from time to time, but not every night.
Work out how to stay on watch for long periods, allowing the off-watch crew to get that restoring sleep. Remember that you also will get that uninterrupted sleep when you are off-watch.
Discuss crew preferences for when to sleep. The age difference and personal preference can be worked to advantage with some creative timetabling.
If short-handed, sail overnight only once or twice each week and allow for a return to the 7-8 hour sleep period in between. After all, it's not a race.
Be aware of your alertness levels. Ask yourself if you are really functioning as well as you would want someone else to if they were in charge and you were asleep below.
FOR MORE INFORMATION
Effects of broken sleep in "shift work" at sea
* Condon, R, et al. (1988). Work at sea: A study of sleep, and of circadian rhythms in physiological and psychological functions in watchkeepers on merchant vessels. International Archives of Occupational and Environmental Health, vol 61, pp. 39-49.
* Hetherington, C, et al. (2006). Safety in shipping: The human element. Journal of Safety Research, vol. 37, pp. 401-411.
* Gillberg, M. (1995). Sleepiness and its relation to the length, content and continuity of sleep. Journal of Sleep Research, vol 4, pp. 37-40.
* Gillberg, M et al. (1996). The effects of a short daytime nap after restricted night sleep. Sleep, vol 19, pp. 570-575.
* Sanquist, T. F., et al. (1997). Work hours, sleep patterns and fatigue among merchant marine personnel. Journal of Sleep Research, vol 6, pp. 245-251.