How sleep quality affects safety on board superyachts

The average person spends about one-third of their life sleeping or attempting to sleep. Sleep is ubiquitous and cannot be removed or significantly altered without detrimental effects. A pioneer in the field of sleep science, Allan Rechtschaffen, once said, “If sleep does not serve an absolutely vital function, then it is the biggest mistake the evolutionary process has ever made.” In other words, sleep and circadian rhythms influence almost every aspect of life, including functioning when awake.

Sleep and circadian rhythms affect human performance, impulsivity, decision-making, learning, memory, attention, alertness, and overall physical and mental health. The demand for humans to perform critical work-related tasks at adverse circadian phases (i.e. biological night – the time when the circadian clock promotes sleep) while lacking adequate sleep has played a role in everyday incidents in the workplace, as well as some of the world’s most devastating industrial and engineering disasters (e.g. Chernobyl, Three Mile Island, Challenger explosion, Exxon Valdez, American Airlines flight 1240, etc.). Every industry where performance, alertness and attention are critical for mission success is affected by the interaction of inadequate sleep and adverse circadian phase (e.g. maritime professionals, military professionals, medical professionals, commercial drivers, first responders, professional athletes, etc.).

The science of sleep and circadian rhythms: A very brief introduction

Sleep and wake, as well as the distribution of stages within sleep, are regulated by two biological processes: homeostatic and circadian.

The homeostatic process reflects sleep “pressure”. In other words, as wakefulness accumulates, the need for sleep increases, and as one sleeps, the need for sleep dissipates.

Circadian rhythms are responsible for the 24-hour cycle in human physiology that favour the timing of events such as sleep, alertness, mood, and hormone release at specific times of day. Thus, the circadian process favours sleep or wake (among other physiological processes) at different times of day relative to an internal daily oscillatory process.

Under ideal circumstances, the result of the interaction between these processes is that sleep is favoured after one has been awake for a full day (biological day) and sleep is favoured and consolidated at night (biological night). Issues arise when circumstances are not ideal.

The importance of sleep quality for yacht crew

Superyacht captains and crews work round-the-clock schedules routinely while at sea. For example, there’s typically at least one crew member fighting their biology to remain awake and alert for anchor watch or passage making.

Over the years, various types of watch schedules have been tried on board private, merchant and military vessels. For example, the so-called five and dime shift pattern was used for many years, which consists of a 5-hour watch and 10 hours in between. However, many vessels are moving away from these types of schedules as it’s becoming clear that schedules which don’t align with the 24-hour daily cycle cause disruption to the circadian system.

A circadian-based watch bill, however, is a term used to describe a work and rest schedule that conforms to a 24-hour day, allowing individuals to work, eat, and sleep at approximately the same time each day. This schedule allows one to align with the naturally occurring 24-hour rhythm that drives all biological processes. In fact, a study compared the 5 hours on/10 hours off (non-circadian) schedule to a 3-hours on/9-hours off (circadian-based) schedule (Brown et al., 2016). The 3 hours on/9 hours off schedule showed enhancements in performance (30% faster reaction times), mood, and reduction in errors (40% to 50%), and daytime sleepiness were observed.

While some progress has been made regarding which watch schedules are better for the circadian system, sleep, alertness and, ultimately, safety on board, more can be done. An ideal watch schedule, coupled with technology that supports circadian alignment for each individual crew member’s schedule, would support sleep and alertness as well as overall wellness and safety on board.

How light can manipulate the circadian