on humans as compared to the impact on the hulls. Tis is normally caused by a phenomenon called bottoming out, meaning that a suspension reaches end of stroke and comes to an abrupt stop. Such events have caused severe injuries and overboard ejections. Amplification can also be caused by single-direction suspensions locking up under exposure to impacts with oblique and lateral forces. Even standing positions aboard
high-speed boats have been shown to amplify human impact exposure (11), potentially up to more than three times higher than the impacts on the hulls. The reason seems to be that impacts taken on straight or almost- straight legs occur after the downward movement of the hull has stopped while the human is still accelerating, in freefall, until heels impact with the deck. At least no other explanation has been suggested. Standing seems especially challenging for the neck, as
cervical injuries reported from boats fitted with standing bolsters seem to dominate over lumbar injuries. This is still an anecdotal observation.
Methods The research method is designed to record impact exposure on both hulls and humans onboard high-speed boats operating in their real sea conditions. Accelerations will be recorded as unfiltered raw data. This will allow for analysis of all characteristics of impacts, potentially relevant for physiological effects and risks of injury. This shall make it possible to assess the significance of other factors than only peak acceleration values, such as rise time (time from 0g to peak g), impact duration, energy content, slam period (time between slams) and force vector (the direction of impact), etc. This will also make the results transparent and possible to scrutinise.
Multi-Agency Study The purpose of the Multi-Agency Study design is to gather sufficient volumes of data to identify correlations between human impact exposure and the occurrence of pain. Tis can be done in a scientifically valid way by using the same study design, protocols, hardware and soſtware across all agencies, and eventually sharing the relevant parts of the resulting data in a common database. By sharing the results, enough data
can be aggregated to achieve significant results, indicating what levels and kinds of impact exposure cause pain. By sharing costs, data and results, great synergies can be achieved and the number of boats, subjects and wave slam events can be sufficient to achieve statistically significant results. Also, the large variation in sea conditions around the world will contribute to the quality of the investigation. Te target is to have at least 10 agencies participating with at least four boats
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scania.com. Ship & Boat International November/December 2018 47
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