Background
Fatigue is characterized by a reduction in physical and mental capability resulting from physical, mental, or emotional exertion. It may impair nearly all physical abilities, including strength, coordination, decision-making, balance, speed, and reaction time. Fatigue occurs due to an imbalance between physical and mental strength during activities and helps the body and brain recover after activities [
1]. Fatigue is experienced frequently among the general working population, with the estimated prevalence being as high as 22% [
2]. Working at sea certainly makes one susceptible to fatigue; therefore, the shipping industry is increasingly concerned about the possible effects of fatigue on personal and operational safety as well as workers’ general health and wellbeing [
2,
3]. Roberts et al. [
4] reported that although the fatal accident rate in the British shipping industry has continued to decrease in recent years, the incidence rate in Great Britain was higher than those among seafarers employed by merchant fleets worldwide. Maritime incidence analyses have shown that approximately 80% of maritime casualties are due to human error [
4,
5], and 26% of shipping incidents are associated with fatigue in seafarers [
6,
7]. Moreover, fatigue, especially chronic fatigue, plays a role in the development of metabolic disorders and cardiovascular diseases. Low-grade chronic inflammation due to chronic fatigue has long-term effects that cause metabolic and endocrine disorders, cardiovascular diseases, autoimmune diseases, and depression [
8,
9].
Watchkeeping and short port turnaround times often increase the frequency of activities, resulting in long and irregular working hours [
10]. The International Labor Organization and International Maritime Organization (IMO) have established mandatory provisions outlined in the Standards of Training, Certification, and Watchkeeping (STCW), in which the maximum number of working hours for seafarers is 14 h per day or 72 h per 7 days [
1,
11]. The International Federation of Transport has reported that 25% of seafarers suffer from fatigue because they work for more than 80 h per week [
12].
The watch officer’s sleeping time depends mainly on the type of watch system implemented. Two fixed watch systems are usually applied: the 4/8 watch system (4 h work and 8 h rest) and the 6/6 watch system (6 h work and 6 h rest). Seafarers are more likely to tire during a shift under the 6/6 watch system than under the 4/8 watch system, especially those with early morning shifts [
13]. Seafarers who work under the 4/8 watch system have better sleep efficiency, more continuous sleep, and a larger number of sleep hours than those under the 6/6 watch system [
14]. The risk of fatigue also depends on the seafarer’s rating, as different levels have different job demands, causing varying fatigue levels. For example, officers may experience high stress levels due to their comprehensive personnel and material responsibilities. However, non-officers face other risks, as they are exposed to strenuous physical activities and job demands [
15]. Regarding the length of service, fatigue is associated with the pressure to work continuously, an increase in the number of jobs, and adaptation to new environments. A shorter duration onboard was associated with a higher risk of fatigue than a longer duration onboard [
16]. Dohrmann et al. [
17] found that fatigue among ferry shipping crewmembers was associated with work-family conflict and poor supervisor support. In their study, these two factors were significantly associated with two subdimensions of fatigue, physical exertion and physical discomfort.
However, Hystad and Eid [
16] found no linear relationship between duration at sea and fatigue.
Additional factors contributing to fatigue are irreversible, job-related, physical factors, such as noise and vibration during working hours and leisure time, which decrease the restorative effect during free time [
15].
Marine sector activities, environments and vehicle types, such as cruise ships, ferries, floating cranes, tankers and other sea and river transportation, are associated with various health and safety risks. For example, the high density of cruise ships in the path of tugboats and the river’s geography, with a winding path and varying depths, increases the risk of accidents on the Mahakam River, Indonesia. In 2017, the Samarinda harbourmaster recorded 13 maritime incidents involving tugboats in the Mahakam River; the incidents ranged from grounding to ship burning and collision. The high incidence of accidents and the lack of investigation into whether these accidents were related to human factors, such as fatigue, warrant a preliminary study to determine factors associated with fatigue among tugboat crewmembers.
Results
Among the 138 respondents selected by sampling, nine crewmembers from 1 tugboat had a prolonged voyage, making it impossible for them to continue participation in this study. Moreover, one respondent could not continue participation due to sickness while on board, and one participant had to leave the ship for family reasons; hence, these participants were excluded from the study analysis. In total, 127 participants, including 57 respondents who worked more than 72 h per week and 70 respondents who worked less than 72 h per week, were included. The crewmembers’ ages ranged from 21 to 60 years. More than half of them were not married (51.2%), were smokers (63%) and consumed coffee (53.5%) and/or alcohol (22.8%). More than 75% of the respondents had poor sleep quality; 54.3% received less than 7 h of sleep per day, and more than 50% experienced work-family conflict.
The study sample comprised 63 officers (49.6%) and 64 non-officers (50.4%), with the majority of respondents under the 4/8 watch system (82.7%). Their length of seafaring experience was ranged from 1 to 35 years, with 55.9% of the respondents having less than 6 years of seafaring experience. Approximately 51.2% of the respondents had a duration of less than 6 months on board. This study also found that 44.9% of the respondents worked more than 72 h/week.
The measurement results showed that 40.2% of the tugboat crewmembers experienced fatigue. Of the 59.8% that did not experience fatigue, 45.7% had a prolonged reaction time without an increased score on the subjective fatigue questionnaire.
Table
1 summarises the results of the bivariate analyses and four variables with a
p-value
< 0.01: sleep quality, work-family conflict, length of seafaring experience, and working hours.
Table 1
Association of tugboat crewmember characteristics with fatigue categories
Age (median; min-max. in years) | 28; 20–61 | 29; 20–56 | 0.76* |
Marital status |
- No | 30 (46.2%) | 35 (53.8%) | 0.16** |
- Yes | 21 (33.9%) | 41 (66.1%) |
Smoking status |
- Medium smoker | 9 (42.9%) | 12 (57.1%) | 0.60** |
- Light smoker | 25 (42.4%) | 34 (57.6%) | 0.52** |
- Non-smoker | 17 (36.2%) | 30 (63.8%) | Reference |
Caffeine consumption |
- > 2 cups/day | 5 (35.7%) | 9 (64.3%) | 1.00*** |
- 1–2 cups/day | 25 (46.3%) | 29 (35.7%) | 0.25** |
- None | 21 (35.9%) | 38 (64.4%) | Reference |
Alcohol consumption |
- Yes | 17 (58.6%) | 12 (41.4%) | 0.02** |
- No | 34 (34.7%) | 64 (65.3%) |
Sleep quality |
- Poor | 45 (46.9%) | 51 (53.1%) | 0.01** |
- Good | 6 (19.4%) | 25 (80.6%) |
Work-Family Conflict |
- Yes | 35 (54.7%) | 29 (45.3%) | < 0.01** |
- No | 16 (25.4%) | 47 (74.6%) |
Watch system |
- 6/6 | 9 (40.9%) | 13 (59.1%) | 0.94 ** |
- 4/8 | 42 (40.0%) | 63 (60%) |
Rating |
- Officer | 20 (31.7%) | 43 (68.3%) | 0.06 ** |
- Non-Officer | 31 (48.4%) | 33 (51.6%) |
Duration on board |
- < 6 months | 28 (43.1%) | 37 (56.9%) | 0.49** |
- > 6 months | 23 (37.1%) | 39 (62.9%) |
Length of seafaring experience |
- < 6 years | 36 (50.7%) | 35 (49.3%) | 0.01** |
- > 6 years | 15 (26.8%) | 41 (73.2%) |
Working hours |
- > 72 h/week | 40 (65.3%) | 17 (34.7%) | < 0.01** |
- < 72 h/week | 11 (24.4%) | 59 (75.6%) |
The following candidate variables that had a p-value < 0.01 in the bivariate analysis were included in the multivariate analysis: working hours, sleep quality, work-family conflict, and length of seafaring experience.
Table
2 presents the multivariate analysis results. Working hours more than 72 h/week was strongly associated with fatigue (
p = < 0.001, adj. OR = 13.32, 95% CI; 4.78–31.23), and a significant association between fatigue and sleep quality (
p = 0.012, adj. OR = 4.49, 95% CI; 1.39–14.52) was noted. In addition, participants with work-family conflict had higher odds of fatigue than those without work-family conflict (
p = 0.028, adj. OR = 2.87, 95% CI; 1.12–7.33).
Table 2
The determinant factors of fatigue among seafarers
Working hours | < 0.001 | 13.32 [4.78–31.23] |
- > 72 h/week | 40 (65.3%) | 17 (34.7%) |
< 72 h/week | 11 (24.4%) | 59 (75.6%) |
Sleep quality | 0.012 | 4.49 [1.39–14.52] |
- Poor | 45 (46.9%) | 51 (53.1%) |
- Good | 6 (19.4%) | 25 (80.6%) |
Work-family conflict | 0.028 | 2.87 [1.12–7.33] |
- Yes | 35 (54.7%) | 29 (45.3%) |
- No | 16 (25.4%) | 47 (74.6%) |
In the bivariate analysis, the length of seafaring experience was significantly associated with crewmember fatigue. However, after adjustment for the three main variables above, the multivariate analysis found that the length of seafaring experience (p = 0.154) was not significantly associated with fatigue.
Discussion
This study found that the fatigue prevalence among tugboat crewmembers in Samarinda Harbor was 40.2%. The related factors were long working hours (particularly those exceeding 72 h/week), sleep quality, and work-family conflict.
The prevalence of fatigue among the subjects in this study was slightly lower than the prevalence among floating crane ship crewmembers reported in a previous study (69.4%) [
27]. This difference might be due to variations in the work characteristics between these two ship types. Unlike a tugboat, a floating crane generally stays in one place for an extended period because of the work nature. Lack of an opportunity to exit the ship to prevent boredom induces a monotonous working rhythm [
16]. On a tugboat, even though the total sailing time may be longer, during times when the ship is loading or unloading, the crew may disembark the boat to shop for food and supplies or for entertainment. It has been shown that boredom effects contributed the most to the performance of crews [
28].
This study found that working hours were significantly associated with fatigue [adj. OR = 13.32; 95% CI (4.78–31.23)]. More than 40% of the study subjects worked more than 72 h/week, exceeding the seafarer working hour limit established by the STCW-IMO 2019 regulation [
1]. This study supports the finding of Salyga [
29], who studied passenger ship crewmembers. Generally, passenger ships use automated systems in their daily operation to minimise fatigue experienced by seafarers.
This study showed that 75.6% of the respondents had poor sleep quality, which significantly increased the likelihood of fatigue [adj. OR = 4.49; 95% CI (1.39–14.52)]. A similar finding was reported by Andhika [
27], who found that respondents with poor sleep quality had a significant chance of experiencing fatigue. Smith et al. [
15] also found that poor sleep quality was significantly related to fatigue. Poor sleep quality contributes to fatigue due to insufficient relief from acute fatigue, and cumulative fatigue eventually progressed to chronic fatigue. Wang [
30] and Jepsen [
31] have proposed that chronic fatigue is due to the accumulation or recurrence of acute fatigue. Watchkeeping duty, especially at night, disturbs sleep, making it challenging to maintain good sleep quality [
17]. In addition, Smith and McNamara [
2] found that sleep quality was affected by ship noise and movement and reported that 44% of respondents considered noise a nuisance.
Similar to Dohrmann et al.’s study [
32], this study found that work-family conflict was significantly associated with tugboat crewmember fatigue [Adj. OR = 2.87: 95% CI (1.12–7.33)]. Further, their study explained that work-family conflict contributed to a heightened risk of physical exertion and physical discomfort in the physical subdimensions of fatigue. Sampson & Ellis [
33] identified that the potential main factors related to family were missing family members and receiving bad news from home. To prevent mental health issues among seafarers, they recommended the availability of confidential counselling services.
Smith [
12] stated that several job conditions, including night shift work, may cause acute and chronic fatigue, decrease awareness and increase sleep debt. Moreover, Lacourt et al. [
8] found that working conditions, including night shift work, changed circadian rhythms, increasing persistent fatigue associated with chronic low-grade inflammation. Furthermore, Chen et al. [
9] noted that chronic low-grade inflammation led to various prolonged stress-related disorders, such as cardiovascular disease, diabetes, autoimmune conditions, and even clinical depression.
The results of the multivariate analysis did not reveal a relationship between the length of experience of seafarers and the incidence of fatigue in tugboat crewmembers. This result is similar to that of Hystad’s [
16] systematic review that found no relationship between the length of experience of seafarers and fatigue in crew members on various types of vessels. They argued that seafarers’ psychological capacity in response to environmental stressors is necessary to cope with the stressful onboard environment.
This study found a nonsignificant association between job rating and fatigue and that non-officers had the same likelihood of fatigue as officers. However, many studies have found different results. Andhika’s study [
27] found that non-officers experienced more fatigue on floating cranes than officers. Smith et al. [
12] also found that non-officers had a higher workload because of their function as technical operators and carried out more strenuous physical activities with longer working hours than officers. Burke [
34] found that officers had relatively more regular shifts and working hours than non-officers. Therefore, the likelihood of fatigue in non-officers was higher than that in officers [
10,
35] These different study results regarding the relationship between job rating and fatigue may be explained by the fact that the tugboats had fewer crew members than the other types of ships in other studies. The small number of tugboat crewmembers makes the workload similar between job ratings, both quantitatively and qualitatively.
This study has some limitations. One of the limitations is the common method bias/variance that was indicated by the final model coefficient determinant, which was not high enough. This study’s potential common method bias might be due to limited candidate variables included in the data analysis, resulting from the bivariate analysis that considered only a p-value of < 0.01. Nevertheless, the sample size is sufficient to answer the research questions. The other study limitation is no direct observation during work-rest time recording.
Additionally, work-rest time data depended solely on the respondents’ answers to the self-completed questionnaire. Potential bias was minimised by cross-checking with the voyage memo. Fatigue assessment is also needed. However, as Volker et al. [
36] noted, there is no existing, agreed-upon single method to detect and quantify fatigue or a robust diagnostic tool to measure subjective fatigue. Finally, this study samples was limited to tugboat crew members; nevertheless, this study’s results might be generalised to other ships’ crew members with similar personal characteristics, tasks as seafarers, and working environments.
Based on the results of the analysis, stakeholders should consider some recommendations. The high prevalence of fatigue among seafarers should be prevented and controlled by addressing the determinant factors enumerated in this study. Some unhealthy habits can aggravate fatigue, such as low-grade chronic inflammation, which increases the risk of metabolic disorders and cardiovascular diseases [
9]. Therefore, workers should improve their knowledge and awareness regarding fatigue and its related factors. Crewmembers should adopt a healthy lifestyle by avoiding smoking and alcohol, consuming a balanced diet onboard, exercising regularly, and enhancing sleep quality through sleep hygiene or strategic napping.
Government agents, especially the harbourmaster, should consider the importance of monitoring working hours to maintain health and safety onboard and raising awareness among stakeholders about the dangers of fatigue in the workplace due to prolonged and irregular working hours and lack of sleep onboard. Marine companies are encouraged to conduct screening for fatigue and hold sleep disturbance management sessions in collaboration with health and safety institutions.
Marine companies should start developing fatigue and working hour monitoring systems and risk management systems as strategies to mitigate fatigue in mariners. In addition to personal psychological support, companies should promote wellness programmes for crew members onboard and enhance sleep quality by improving ship accommodation facilities and maintaining good housekeeping.
The four variables included in the multinomial regression analysis accounted for 49% (Nagelkerke R2 = 0.49) of fatigue, which means that further studies are needed to explore additional variables accounting for to the remaining percentage, including sub-dimensional measurements of fatigue.
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