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Feature 1 | PATROL AND RESCUE BOATS Are you sitting comfortably?


Severe bow motion and wave slamming can cause spinal injuries to crew members on fast patrol and rescue craſt, prompting the industry to look at ways to improve seating to minimise the impact.


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mong the health risks associated with high-speed patrol and rescue boats are the deleterious effects of


wave slamming on members of crew. Facing harsh weather conditions – particularly in areas of Northern Europe and the Baltic Sea – and travelling at speeds of up to 40-50knots, the hard slamming of these vessel types against the waves can increase the susceptibility of onboard personnel to spinal injuries. It can be hard to ascertain the exact


extent of the problem: as Dr Tom Coe, naval architect at Frazer Nash Consultancy, tells Ship & Boat International, there has not been a huge amount of research into the effects of slamming on high-speed vessel crews. However, he does draw attention to some disturbing findings from the US. “One American surf boat rescue operator survey revealed that the amount of injuries sustained by crew was 10 times the average of that experienced by the US Coast Guard [USCG],” he says. “The workdays lost to injuries were also 10 times greater than those of the USCG, with the most commonly reported injuries being those to the spine, shoulders, lower back, knees and neck.” In the UK, he adds, the Royal National Lifeboat Institution (RNLI) has estimated that between 50-70% of seafarer injuries sustained in extreme working environments can be attributed to the effects of the bow motion of the vessel, with shocks being transmitted to the spine via the seat interface. “In some cases of health complaints


aboard fast patrol vessels, we’ve noted that the suspension seats had already ‘bottomed out’, with the spring and damper working at minimal performance levels,” Coe continues. “When operating in rough weather, this could prove more harmful than having no suspension seat at all.”


Safe resonance In turn, Frazer Nash Consultancy has developed an innovative seat type, named the Frazer Nash RNLI Seat in recognition of


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The Frazer Nash RNLI Seat is intended to minimise the transmission of severe


shock loads, to safeguard patrol craft operators’ shoulders, backs and necks.


the group’s initial work with the life saving organisation in developing a solution for its rescue boats, particularly in minimising the transmission of severe shock loads. Commencing development in 2000, Frazer Nash spent the next five years fine-honing the seat type for use aboard the RNLI’s Tamar class lifeboat, and these seats were included on board when the first-in-class of this series went into active service in 2006. “We used a combination of modelling the


boat motions with the HydroDyna system and comparing this data with the prototype data on the vessel,” says Coe, explaining how the group used this information to optimise the spring and damper to reduce shock. Frazer Nash Consultancy also looked into


the science of human resonant frequency as an important set of parameters, when considering the seat design. Put simply,


humans are exposed to a certain level of vibrations at all times, and this level naturally increases should the person enter a vehicle, be engaged in labour, and so on. A safe human resonant frequency is typically 4-6Hz, aſter which the human body starts to resonate, which can increase the risk of injury. Te group factored this into its modelling and testing, and, as a result, Coe claims that the seat has managed to lower its damage predictions to a tenth of that of conventional patrol craſt seats. The Frazer Nash RNLI Seat has since


found its way aboard BP’s North Sea oil platform rescue boats and QinetiQ’s Partial Air Cushion Supported Catamaran Innovative Solution Demonstrator Craft (PASCAT ISDC), a fast landing craſt which has been deployed in sea trials by the UK Ministry of Defence. SBI


Ship & Boat International March/April 2012


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