|
Test-candidates were 32 experienced watch-officers.
Each of them had to make 2 runs, one early in the morning (07.30 AM) when they just finished a good sleep, and one at 3 a.m. when they had been kept awake for 21 hours.
Loss of overview due to preoccupation with the distracters was measured as the number of crossings of a buoyage-line, a surface area formed by "safe water limits" and the route outside these limits.
Furthermore, data were available on the latency of reactions on events and the number of task-interruptions during the events, as measures for rigid behaviour. In the subtests with traffic incidents, the closest passing distance (CPA) was available as a measurement of risk taking. Qualitative reactions on the events were also available.
For this part of the research the following hypotheses were tested:
Fatigue is expected to have the following behavioural effect on operations (in short):
・increase in loss of overview
・increase in aversion of effort
・more behavioural rigidity
・more risk-taking
Some results (in short):
Participants did not cross the buoyage more often in the fatigue- condition compared to the rested condition. The surface area of the deviation route that participants sailed outside the SWL also did not differ
Fig.8 : buoyage crossings/deviation areas
The reaction latency on events was in general not larger in fatigue- as in rested condition. This is also true for the number of task-interruptions. The CPA in rest-condition appeared to be larger in fatigue condition
Fig. 9: reaction latency on incidents
In the subtests at incident-level a few trends were as
expected:
・Fatigue participants noticed in subtest B approaching traffic later then the rested participants (215.14 versus 97.93).
・In subtest B, fatigue operators tend to react slower than the rested operators ( 150.17 versus 68.20 sec).
・In subtest C fatigue participants reacted later than rested operators ( 1.50 versus 0.19 see).
・In subtest D fatigue operators reacted slower than rested operators ( 259,67 versus 120.29 sec).
Overview reducing effects of the different distracters were as expected: a linear increase of buoyage crossing. (but not really significant). The deviation area did not show the expected increase over the subtests.
Fig. 10: buoyage crossings
Fig. 11: deviation area (NM)
A false conclusion from these experiments may be that the performances of watch-officers do not suffer from fatigue. One of the reasons why statistical evidence was hard to get was the large reaction variance within subjects. Also between operators, reactions on fatigue after 21 hours without rest were very different:
Some officers were easily irritated in conversations, others could not maintain overview when sailing in not known areas, and some became inaccurate and risky. In the control subtest some had a hard time in staying awake in the dull environment without alerting events.
Conclusions (in short):
・The effects of aversion against investing effort and the increased rigidity to reduce tasks-switching were hard to establish
・The longer reaction latencies on events were not enough to reduce overview
・Less risk was taken when operators were fatigued
・In contrast to the expectations, passing distances were larger when fatigued
Some discussion on the findings and conclusion is needed for further experiments:
・The officers were used to shiftwork
・Not all were fatigue enough after 21 hours of no rest
・One day of no sleep is not enough.
・There were not enough "ship-stressors like motion, noise and smell.
・The fact can be that the Brisim III subtests were too short to have hindered fatigue effects to come on top.
・Fatigue effects were visible but not enough for scientific conclusions.
・During the morning sessions several operators were still groggy and not mentally fit; they were up more then half an hour and should not have performance problems anymore, but this was not the case.
More research is certainly required to reveal the fatigue effects during realistic ship's bridge operations.
|
