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Human factors in the design of high speed marine craftD.Nikolić1, R.Allen1, R.Collier2, L.Collier2, D.Taunton3, D.Hudson3, R.A.Shenoi3

Description of the research

Aim of the studyThe main objective of this study was to establish if there is a relationship between boat motion during transits and measures of human physiology. A secondary objective was to establish if exposure of a human to random and shock vibration affected a measure of spinal muscle fatigue and a participant's rating of perceived exertion (RPE).

MethodologyAn experiment was conducted in order to establish if synchronised measures could be used to establish relationships between boat motion during transits and measures of human physiology during exposure to random whole-body vibration in a dynamic environment and to analyse its influence on human physiology.The experiment was undertaken during a sea trial with a RIB-X Expert XT650. A male participant (26 years old, 170 cm tall and 72 kg weight) participated in this study. The time duration of the trial was approximately 30 minutes at an average boat speed of 25 knots. Sea conditions were moderate (sea state 3) with the average wave height of

0.84 m and zero-crossing period of 4 s taken at the closest wave recorder. The data measured during the trial (Figure 1) were:

boat vibration and motion (LCG acceleration and heading),

human whole-body vibration (head and seat acceleration),

human physiological data (electromyography (EMG) activity of spinal muscles and electro cardiographic (ECG) changes).

Perceived exertion using the Borg Rating of Perceived Exertion (RPE) scale was recorded following the trial.

Collaboration

This multi-disciplinary project was carried out as a collaborative endeavour involving:

1. Institute of Sound and Vibration Research (ISVR), University of Southampton

2. School of Health Sciences, University of Southampton

3. School of Engineering Sciences, Ship Science, University of Southampton

4. The Royal National Lifeboat Institution (RNLI)

5. University College Chichester

The research was funded by EPSRC (grant no. EP/C525728/1).

Impact of the research

Designers of high speed marine craft, biomedical engineers and human performance specialists aim to establish guidelines for design of such craft that take into account the need of the crew to maximise performance.

It is anticipated that this translational methodology could be used to enable a better understanding of:

how fatigue develops as a result of exposure during transits,

fatigue characteristics of spinal muscles,

how fatigue impacts human performance,

how to reduce fatigue through preventative exercise measures.

Results and discussion

Whole-body vibrationThe total Vibration Dose Value (VDV) of 12.28 calculated from seat acceleration was dominated by y-axis (12.19) with a contribution from x and z-axes (2.08 and 4.92). This exceeded the Exposure Action Value (EAV) of 9.1 m·s–1.75 19 minutes into the trial. Plot of the frequency-weighted seat acceleration in the most prominent axis along with the corresponding VDV is given in Figure 2, where the EAV and Exposure Limit Value (ELV) are marked by dotted lines.

ECG analysisPlots of boat speed, normalised frequency-weighted LCG and seat rms acceleration magnitudes with a plot of normalised instantaneous heart rate recorded during the trial are given in Figure 3. Results showed a statistically significant correlation between boat vibrations and the heart rate variations. The relationship is evident in the three vibration axes. The influence of the boat vibration with the correlation coefficient of 0.52 is larger than the seat vibration with the correlation coefficient of 0.45. The delay between the heart rate and vibration signals was estimated to be approximately 2 s.

EMG analysisMedian frequencies (MDFs) calculated for the whole duration of trial

Figure 1. Experimental setup (A – LCG Accelerometer, G – LCG Rate Gyroscope, H – Head Accelerometer, S – Seat Accelerometer)

Figure 2. Vibration dose value in y-direction for sitting posture

Figure 3. Boat speed, frequency-weighted seat and LCG rms acceleration magnitudes and heart rate during trial

Figure 4. Median frequencies of the four EMG signals recorded during trial

are shown in Figure 4. It can be seen from these plots that the MDFs of the lower back spinal muscles, i.e. Left Multifidus and Right Multifidus, decrease with time showing a cumulative effect consistent with muscle fatigue.

SummaryThe EMG and ECG changes during vibration exposure were used as a basis for evaluation of fatigue. RPE measures indicated that the participant rated the exertion as “somewhat hard” during the transit and changes in the EMG and ECG signals indicated that fatigue was associated with the transit. This experiment demonstrated that it is feasible to simultaneously measure human performance and boat data, and that there is a relationship between the boat motion and subsequent fatigue.