craft must operate in both heavy and light sea-state and craft speed environments,” he explained. “What might work well to protect the operator during a high shock environment may not be ideal for a low shock environment and vice versa.” Seaspension Technologies in Largo, Fla., produces shock mitigating seating equipped with a patented damper and coil system that automatically reacts to the force being exerted on it. “We basically had a global damper manufacturer tweak an existing shock absorber with our input,” said company President Peter Burer. Seaspension, which started in the recreational boating market, first supplied shock mitigating seats to the Canadian Coast Guard around eight years ago. “We’ve had no failures with these shocks,” said Burer. More recently, Seaspension delivered custom shock mitigating seating for use in 35 U.S. Coast Guard specialized emergency rescue airboats, known as Iceboats. The tripod-mounted seat is designed to protect the crew from jolts experienced when the boat transitions from land to ice and water, and during operation in rugged conditions. Seaspension also has supplied seating to Edgewater Power Boats of Edgewater, Fla., for vessels that were delivered to the Trinidad Coast Guard. Active Shock LLC of Manchester, N.H., which concentrates on shock absorbers in the automotive space, developed a device for the U.S. Special Operations Command designed to be incorporated in a rigid inflatable boat (RIB). That project, developed under a SBIR grant in 2008, has not been acquired by the U.S. military. “What makes our shock absorbers unique is that they are controlled by computer,” said Scott Martineau, the company’s director of business development. “We use sophisticated algorithms that take information from a suite of sensors contained in the shock absorbers themselves to determine the optimum damping rate. In high sea states, the sensor can detect when the boat goes airborne and prevents the seat from bottoming out and transmitting the shock to the crew.” Seaspension, meanwhile, will soon be introducing a shock mitigating seat for use as either a bulkhead seat or as a replacement for the Marine Corps’s 11-meter RIB. “The damper system will allow anywhere from the fifth percentile female by weight to the 95th percentile male in the Marine Corps to be seated and protected from shocks without the use of tools or any kind of adjustment,” said Burer. That would cover women as light as 100 pounds to men as heavy as 250 pounds. “The mechanism in the damper responds directly to forces,” said Burer. “The Navy is looking for a seat that can accommodate different sizes of personnel on a variety of missions subjected to different sea states without having to adjust the damping mechanism.” Seaspension’s new device uses a dual-damper system in order to accomplish that task. “We found it better to incorporate two independent shock absorbers to regulate those weights,” said Burer. “The seat is designed to be able to slip right into existing craft in the inventory of U.S. special operations and foreign militaries as well.” The principles central to shock mitigation are applicable not only to seating and the protection of crewmembers, but also to the protection of equipment mounted on vessels. “We are working on several new applications for our pedestals to be used as weapons and equipment platforms,” said Burer. “We recently bid our heavy duty pedestal as a mount for a .50 caliber gun on a 100-boat contract. We expect shock mitigation to be used much more in this application in the future and are actively testing and designing products to meet this demand.” 14 | SOTECH 8.9 Taylor Devices makes shock mitigation products that have been used on Navy warships for shock isolation on missiles and missile systems, radars, electronics consoles, boat davits, and for recoil isolation on heavy machine gun mounts. These “soft mounts,” which are a combination coil spring and hydraulic shock absorber, reduce the firing recoil from the .50 caliber heavy machine gun from 4,400 pounds to 500 pounds, according to Taylor. This allows the .50 caliber guns to be used on smaller combatant craft. The application of shock mitigation technologies can have the unintended side effect of allowing crews to push a vessel to the limits of its performance, a phenomenon which has both positive and negative implications. As crews become more comfortable, they push the boats harder, and as they push the boats harder, the more they are likely to be subject to additional wear and tear. That is especially the case when shock mitigation has been retrofitted onto a legacy platform. “As operators feel secure in the seat and comfortable at higher and higher speeds they have been driving the boats faster,” said Gezari, referring to the Mark V. “This allows them to run their missions faster and more successfully. But the boats have also experienced structural issues as a result.” For Holmes, special operations crews will best benefit when vessels are properly designed and evaluated for their shock absorbing properties from the beginning. The Special Operations Craft Riverine, he pointed out, does not have the same history of musculoskeletal, boat-related injuries as the Mark V or the Naval Special Warfare Rigid Inflatable Boat (NSW-RIB). “Health monitoring of the shock environment in manned areas of combatant craft needs to be implemented on all combatant craft,” said Holmes. “Monitoring of the shock environment will provide data that will be used to assist future research and measure how effective proposed systems are against mitigating shock.” Research is yielding a set of emerging standards that will likely find eventual widespread adoption and which will help in the measurement of the shock conveyed to the human body through vessels. The International Organization for Standardization, a Switzerland-based group, has released ISO 2631-5, a standard to measure vibration on the human body over time. Another emerging industry standard relating specifically to shock mitigating seats is known as SED-8 and is based on another ISO standard. “SED-8 measures the amplitude and frequency of incoming impacts and then measures the outgoing response” of the seat, explained Burer. “Different seat manufactures employ different kinds of tests to measure the shock absorbing capacity of their systems. With this standard, we can measure the effectiveness of the damper system.” At some point in the not too distant future, Burer predicted, a certification program for shock mitigating seats under SED-8 will be established. Meanwhile, NSW will be assessing all future combatant craft for operator exposure to shock levels that could cause musculoskeletal, boat-related injuries, said Holmes. The current combatant craft, medium requirements document contains a maximum spine stress dose shock exposure level, as defined by SED-8 and ISO standards. O For more information, contact SOTECH Editor Dave Ahearn at davea@kmimediagroup.com or search our online archives for related stories at www.SOTECH-kmi.com. www.SOTECH-kmi.com
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