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sets, cover greater distances at higher speeds, improve crew performance and extend operational effectiveness. It is important to learn from other sectors that have made progress with shock mitigation, but myths need to be dispelled. From motion analysis metrics on land, sea and aircraft, it is clear that not all vehicle impacts are sim- ply lesser or greater G forces. A major difference between automobiles and boats is the suspension system managing vibration between road wheels and the chassis. Trucks take this a stage further and have suspended cabs, so the seat is mainly for comfort. An agricultural or mining vehicle driv- ing over rough terrain experiences different loads to a boat at planing speed on rough water. In recent years, the de- velopment of MRAP (Mine Resistant Ambush Protected) military vehicles has accelerated research into reducing the effects of mine blast. However, a vehicle seat that mitigates the shock from a mine blast is unlikely to mitigate the re- peated slamming effect from high speed wave impacts. Aviation has researched shock mitigation and the ef- fect of various impacts. Helicopter seating is designed to protect the crew from hard landings and a crashworthy seat is part of the overall crumple zone. Ejector seats have saved the lives of many pilots and navigators as they exit from fi xed wing aircraft. However, ejection is a single event based on a consistent input force, usually initiated by the seat occupant, and compared to loss of life, some level of injury may be acceptable. Large wave slams at sea are not usually isolated events, they can be of random magnitude and from multiple directions. In rough sea transits, the boat suspension seat has a fraction of a second to return from a ‘hit’ to mitigate a ‘double hit’ or the next pattern of multiple impacts. A core component of fast boat training should be spe- cialist knowledge to educate coxswains and crews to un- derstand the forces that affect a planing craft, particularly when operating in waves. For planing craft there are three conditions to consider – displacement speed, getting on or off plane, and planing speed. When loitering or at slow speed in waves a craft follows the waters surface, the hu- man response is unlikely to be injury but could be motion WORKBOATS www.marinelink.com MN 71 MN Nov14 Layout 66-81.indd 71 10/27/2014 9:45:23 AM
