Two methods of assessing the discomfort created by vibration on a river ship
The discomfort during the voyages is a subjective reaction of the navigating personnel thus it can be divided in: overall discomfort – only for longitudinal, transverse and vertical accelerations, the total discomfort, rated on a scale of 1 (high discomfort) to 5 (small discomfort) and harmful discomfort – motion sickness due to prolonged low frequency. This paper analyses the comfort for 4 persons who are part of the crew of a river ship on the Danube, depending on the dynamic variables (accelerations measured with the accelerometer). The determinations were made according to ISO 20283-5 (Measurement of vibration on ships). Whole-Body Vibrations characteristic quantities were calculated: timeweighted accelerations, time periods after which the exposure value that triggers the action and the exposure limit value, Sperling's comfort index and Comfort Note. The Comfort Note differs substantially from Sperling's travelling comfort index. If the average of the latter is 2.284829, that is near an average comfort on a scale of 1 to 5, the average Comfort Note is 4.16413 (on the same scale) – that is a very poor travel comfort. Given that time-weighted acceleration values are in the range 3-4 m/s2, with an average of 3.72 m/s2 – that is more than twice the limit of discomfort (1.15m/s2) – it can be concluded that the assessment of the comfort of the crew members is better done by using the definitions for the Comfort Note than those for calculating the Sperling index for travelling comfort.