There has been very little investigative work on the ergonomics of the tasks performed by seafarers, at least in merchant shipping. Much of the relevant work has been done in military settings or has to be extrapolated from similar onshore tasks.

 Other sectors of transport are characterised by a well-defined ‘work station’ such as the aircraft cockpit, the train cab or behind the wheel in a car. Other facets of work in these sectors are seen as belonging to other occupations such as maintenance and the supply of food and overnight accommodation. In seafaring all these are integrated, hence it is a complex environment to investigate.

 Task analysis is an important but neglected area of maritime research, touching as it does on sensitive topics such as job demand and job control, cognitive overload and underload, the effects of abnormal working schedules and fatigue and the social and organisational dimensions of work at sea. This latter aspect has received some attention recently in what is characterised as ‘the human element’ in seafaring. It has found its expression in approaches borrowed from other sectors such as ‘bridge resource management’ an aviation lookalike. This has recently become a priority as it is seen to be a potential contributor to the reduction in maritime disasters and major accidents.

 In terms of the practice of maritime health there are many other less high profile aspects of the ergonomics of work at sea which either determine the limitations to work for some of those with health related impairments or contribute to the occupational health risks in seafaring. A number of these are covered in other sections of this publication and the purpose of this section is to outline a few of the principles that underlie ergonomic analysis and to note some of the problems relevant to maritime health that are not noted elsewhere.


The ergonomic loop 

Virtually all work and conscious leisure activities can be thought of in terms of the following sequence:

 Sense organs, most obviously the eyes and ears (hearing, inertia and balance) but also the skin, stretch receptors around joints and the chemoreceptors of the nose and mouth receive and transduce information into nerve impulses which are transmitted to and analysed by the central nervous system.

  1. The cognitive processes in the brain interpret the significance of the patterns of impulses, prioritising them in terms of urgency and then matching them against innate and learnt templates to establish whether a response is needed and if so what it should be.
  2. An executive decision on the response usually translates as motor nerve impulses to muscles and other structures to direct the body to take appropriate action. This may be the primary action needed to deal with a situation, or it may be a necessary interim stage such as adjusting the eye muscles to so that the source of a sound can be viewed and so be better interpreted.
  3. As in stage 1 the sense organs monitor the body’s response in terms of changed position and effects and then adjust it as needed to refine the action taken or to adapt to its consequences.

 This loop can be clearly perceived in tasks based on a ‘work station’ such as driving a car or working at a supermarket checkout but exactly the same principles apply when watchkeeping on a ship’s bridge, serving food to crew and passengers or maintaining an engine room pump. Its importance for maritime health lies in the details of the performance requirements to perform tasks as analysed at each of the stages of the loop. Thus impairment of colour vision will adversely affect recognition of colour coded items, especially dimly illuminated navigation lights: fatigue will make the cognitive response to any lights perceived less well structured. Similarly the inertial shifts on a moving ship will make the task of a waiter pouring coffee for passengers far more complex with a higher chance of a stylish pour missing the cup.

 The performance limits of most people approximate to a norm, but there are differences. Some of the physical ones relate to age, size and fitness, while the cognitive ones are a mix of innate abilities and of the quality of education and training. Current or potential health related impairments can be important contributors to such limitations.


Routine and emergency duties


Most seafarers have two very different categories of task, those that they perform on a daily basis and those that only arise in an emergency. Because of the nature of routine duties seafarers’ capabilities for them are tested regularly and a necessary level of fitness and competence is likely to be maintained. Here, given an initially adequate level of capability, performance is only likely to either decline slowly as a consequence of aging or to be suddenly interrupted by an incapacitating event or illness. It is feasible to assess slow decline, for instance in vision or hearing, in the course of periodic medical assessments. Recognition of the likelihood of incapacitation, either sudden, as with loss of consciousness from a neurological or cardiac cause or over a few hours from recurrence of an illness is necessarily a probabilistic decision based on the person’s prior history of disease or signs observed during medical assessment.

 Emergency duties are characterised by greater physical demands that have to be carried out rarely and under conditions of threat and fear, whether they are fire fighting, rescue, personal survival at sea, unplanned repairs or damage control on the vessel. Here strength, stamina and psychological stability will be required and it is the reserves of these attributes that need to be considered, insofar as it is possible, in the course of a medical assessment. Probably the commonest current problems in relation to emergency duties are the consequences of obesity for cardiorespiratory reserve, ability to perform demanding task such as entering a life raft and a simple inability to fit into safety equipment such as life jackets. 

Impairment, medical conditions and task demands


Almost all the safety and performance related aspects of health assessment can be mapped against the stages of the ergonomic loop. It is important to recognise that the whole purpose of the seafarer medical assessment is to make predictions about functional ability. This is a different outcome from that with which most clinicians are familiar; where prevention, diagnosis and treatment are the prime purposes. For this reason it is important, whenever seeking a medical report from a clinician, to assist with a fitness decision, to emphasise that what is required is a prediction of functional ability and how it may change in severity over time and not primarily a diagnosis or a treatment plan, except insofar as the treatment itself may affect function.

 1. Sensory reception. Most sensory impairments are static or only slowly progressive. Shorter-term incapacitation is seen with a few eye conditions such as recurrent retinal disease and with some disorders of balance. E.g.

-vision testing: acuity, colour, fields, low light vision/glare

-eye disease

-hearing testing

-ear disease including disorders of balance

-skin sensation


2. Cognition. Stable impairments can occur with a few neurological conditions and after events such as stroke. Fluctuating or rapidly impairing effects are more frequent. Eg.

            -psychoactive medication

            - alcohol and drug misuse

            -sleep disorders/fatigue


            -cardiac arrhythmias

            - acute arterial disease – heart attack, stoke, TIA.


            - hypoglycaemia

            -consequences of mental ill-health

3. Execution of actions. Many limitations are stable, some fluctuate over time, pain may suddenly limit actions, reserves of strength and stamina important. E.g.

-bone, muscle and joint disease


-neurological conditions e.g multiple sclerosis

- reductions in cardio-respiratory reserve. Chronic lung disease, reduced cardiac function




When assessing an unfamiliar condition, consideration of the stages in this sequence and analogy with the conditions listed above may be a useful aid to decision taking.




Vision can be assessed using standard tests of acuity and colour vision and this is the routine practice.[i] Many of these tests do not directly relate to the sort of visual functions needed to cope in conditions of poor visibility and at night but they are simple to apply.[ii] Hearing loss can be identified either by finding thresholds for pure tone sounds or by means of speech comprehension.  The actual contribution of the use of particular levels of visual or auditory capability as the basis for decisions on who is able to undertake navigating duties does not have a well-validated basis beyond the empirical fact that both functions are essential for safety when navigating a vessel.

Cognitive abilities are critical to the correct interpretation of information from both within and beyond the vessel. Assessment of cognitive function is largely outside the scope of the medical examination process and usually depends on the person’s observed performance at their job. However, in a few cases, for instance following a head injury or cerebrovascular event, or when there are concerns about a seafarer’s performance and they are referred for a medical review of the current state of cognitive ability may form part of a medical examination, referral for more detailed psychological assessment is often required. Behaviour traits, such as impulsiveness, aggression and risk taking, can also influence cognitive processing in ways that are particularly likely to put a ship into danger and again a specialist assessment will probably be needed. These traits are likely to come to the attention of those performing medical examinations either because of a clinical report, or as a result of concerns about performance while in training or while at sea. Mental ill-health can also adversely affect cognitive performance and this is likely to be exacerbated by any concurrent misuse of alcohol or drugs.

Sudden incapacitation in a navigating officer or rating can have direct consequences for vessel safety. A significant excess risk of an incapacitating event such as a loss of consciousness from reduced cardiac function, seizure or insulin induced hypoglycaemia will limit a person’s suitability for navigation duties. If adaptations, such as the constant presence of another crew member competent to take over their duties is feasible it may be possible for them to continue to work.

Physical abilities beyond a baseline level are not directly relevant to navigation duties as such, but the officers and ratings who perform navigation watches usually have other duties, for instance vessel inspection tours, cargo handling and mooring that require agility, manual handling capabilities and stamina, all of which need to be assessed  


Prolonged voyages


Seafarers onboard a ship, except when it is in port, rarely have access to medical care. The one exception to this being those serving on vessels with more than 100 people aboard – almost exclusively cruise ships – and even here, although there will be a doctor and a medical centre, the full range of facilities is not available. As a consequence any illness, or indeed injury, that arises has to be managed by crew members who have only limited training and who also have other duties to perform until the ill or injured person can be disembarked. The arrangements for their training, for medications and medical equipment to be carried and for access to advice, both from medical guides and from onshore telemedical services are covered in chapter 9.

 Selection procedures for seafarers who are on long voyages that are out of reach of the shore need to identify any pre-existing condition that could be expected to recur, relapse, progress or have complications while at sea. A judgement needs to be made on the probability of this happening and on the importance of early onshore medical care to survival and recovery. Some account also needs to be taken of the likelihood of severe pain, which even if not life threatening, as with a dental abscess or a renal stone, will create major distress for the individual and a high level of concern among other crew members.


Examples of relevant risks:


- Cardiac event

- peptic ulcer

- biliary colic

- renal colic

- low back pain

- pneumothorax


- multiple sclerosis

- mental health problems

- obstructive lung disease

-ulcerative colitis


- diabetes

- cardiomyopathy

- liver disease

- kidney disease


- hernia

- poor dental health

- prostatic hypertrophy


The presence of one of the above conditions does not automatically make a person unfit to undertake long voyages, but the risk of serious problems arising at sea needs to be assessed in each case, as does the importance of rapid intervention should a problem arise.


Watchkeeping schedules


Most seafaring is a 24 hour activity. As a consequence, seafarers work for periods at all times of the day and night and may also work many more hours per day than would be normal onshore. There are legal restrictions on hours worked, but emergencies, pressure to arrive on time, crew reductions and at times the urge of seafarers to maximise their wages will lead the boundaries of the law being exceeded.  See 10.16 on fatigue. The scope for medical assessment of a seafarer’s suitability for watch keeping duties is limited. Adaptation may become more difficult with age as sleep patterns become more disturbed, sleep disorders such as obstructive sleep apnoea may mean that a regular daily pattern of rest is essential. Irregular eating habits can adversely affect some gastro-intestinal conditions. Medication regimes are normally based on regular periods of sleep and wakefulness and these can be difficult to adjust. However, in most cases it is the subjective feelings of the seafarer about how well they are coping with watch keeping duties that will determine advice and decisions about fitness for watch keeping.


Emergency duties


Most crew members will have duties in the event of a maritime emergency such as a fire, collision, grounding or storm damage. These often require physical capabilities and mental resilience over and above that needed during routine duties. Medical assessment of these abilities beyond physical fitness testing is rarely practicable but training courses in fire-fighting and safety of life, as well as emergency drills onboard provide indicators of ability. If these courses have not been undertaken recently re-attendance may be a valid form of assessment. A medical declaration of fitness to participate in such courses in mid-career may be required by the course provider. 

 Physical capability testing has several dimensions: cardiorespiratory reserve as tested by step or treadmill test; muscle strength, joint flexibility, co-ordination of movement and balance. It is usually best carried out in a gymnasium rather than in a clinical setting, except where detailed medical monitoring, for instance for cardiac performance, is needed.


Fish catching


Fishing requires a large proportion of the crew of the vessel, whether small and inshore or larger and fishing in distant waters to be on deck handling gear and the catch, often under adverse weather conditions. These tasks are physically demanding and so in principle a rational assessment process would identify those with poor physique or mobility problems as well as those whose health could be adversely affected by exposure to hot or cold conditions. In practice most of the people worldwide who work on fishing vessels self-select into the work and continuity of employment depends on having the appropriate physical and mental capabilities.

 For distant water fisheries the same considerations apply as to any other long voyage (7.2), while for those who navigate fishing vessels the functional requirements are the same as for all other seafarers with these duties (7.2).


High-speed vessels and fast craft


This covers a variety of types from high-speed ferries to inflatables used for rescue and patrol work. With the exception of customer service staff on fast ferries virtually all crew members will be undertaking navigational duties, but in a situation where fast response times are essential to take account of sea conditions. The criteria will be as 7.2 but where, as on small inflatables, there is no crew protection, the use of glasses to aid vision can be a problem because of spray on the lenses.  In addition there is a considerable amount of whole body vibration and this means that any musculo-skeletal problems, especially those affecting the back and neck are likely to be worsened. It is therefore good practice to screen for these conditions before starting work in fast craft and to consider excluding those with severe problems. The effects of vibration on those working in fast craft should always be assessed when they are medically examined.

 If the craft has rescue duties it is important to ensure that those working in them have the physique and stamina required to ensure that the rescue team can work effectively. Such crafts often have only limited protection from the weather for crew and, even when this is available, rescue operations will involve exposed work, often in very adverse weather conditions. Hence any excess risks from cold exposure need to be considered.

 Fast craft normally return to shore on a daily basis so there is no significant risk from the presence of any medical condition that will only lead to health problems which develop over a period of days (7.3).


Sail ships


Much sailing is done in the leisure sector and so does not feature in fitness for work assessment and certification. However, commercial yacht masters and crews and those who act as officers on sail training ships usually come within employment related assessment regimes. Even for those who crew such vessels for pleasure there will be situations where an assessment of fitness is appropriate. The requirements for handling sails will vary with rig, but specific physical capabilities may be required to handle wet sails in poor weather and to go aloft.

 The requirements for navigators are as in 7.3 with the addition that these duties are often carried out in the open rather than on a bridge and so the ability to cope with adverse weather conditions is important. On smaller commercial charted yachts there may only be one commercially qualified yacht master, with the other crew members being effectively paying passengers with no guaranteed seafaring skills. In these circumstances sudden illness in the qualified yacht master is likely to have major implications for vessel safety and they should only be considered fit if they have no significant excess risk of incapacitating illness. Where vessels are on prolonged voyages assessment should take account of 7.3.