Feature 4 | PATROL AND RESCUE BOATS Figure 2 Fixed seat


100 200 300 400 500 600 700 800 900 1000


0 0 2 4 6 Impact peak acceleration (g) 8 10 12 Suspension seat


942 impacts Going up to 12g


481 impacts going up to 4,6g


Te graph in Figure 2 shows significant


differences in impact exposure on two similar boats, fitted with different types of seats and run side-by-side over three hours. Measured as peak acceleration plotted as (g), 9.81m/s2, the number of impacts was double (481 vs 942 impacts) and the difference in amplitude of the highest peaks was 2.6 times higher (4.6 g vs 12g) for the fixed seats. The overlaid columns illustrate the


Expressed as VDV 33,8 vs 36.8


same data measured as VDV, showing an insignificant difference in exposure, just 9% (33.8 vs 36.8) (11). Impact exposure differed significantly


of injury alters the geometry and may result in neurological damage and permanent disability. When stabilising structures are


damaged, neurological symptoms may occur instantly or develop over time, and also come as results of a repeated impact. In any case, pain is present as an indicator of acute injury, and acute pain should be considered as a sign of possible injury – damage to anatomical structures. Pain can be present without


injury, but acute injuries rarely occur without causing pain.


Physiological effects A study of human impact exposure, comparing suspension seats to fixed seats (10), showed twice the number of impacts and three times the peak impacts levels when using the fixed seats. Aſter three hours of exposure at sea, physical performance, measured by shuttle run test, was reduced by more than 30% in the more exposed group.


between the two groups. Those in the fixed seats received twice as many impacts as those in the suspension seats. The impacts were also almost three


times as high on the fixed seats as on the suspension seats. Tis difference in exposure correlates well to the effect on physical fatigue. However, with this same exposure


data processed and presented as VDV, there was no significant difference: 33.8 versus 36.8. Many suspension seat types, often


called ‘shock mitigation’ seats, have been shown to increase impact levels


Figure 3: Deck-to-L4 Standing Transfer Function. The graph was created using deck and back data from sea tests of a NSW 11M RIB, showing an aerage of  amplfiaton and a mamm for tmes hgher mpats on the hman than on the hllde


46


Ship & Boat International November/December 2018


Sum of impacts (n)


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