When the U.S. Navy needs to transport a large number of sailors at the same time, they often use a hovercraft. However, that presents a challenge. “You can’t go on the hovercraft deck while it’s flying across the water, so you have to put a portable building on the deck to accommodate up to 180 people,” says Rob Banerjee, president of NexGen Composites LLC in Franklin, Ohio. “That’s where we come in.”
NexGen supplies the U.S. Navy with 21 x 42-foot personal transport modular (PTM) shelters made from composites. The shelters are constructed from individual panels measuring approximately 7 x 7 feet that connect mechanically. Once assembled on the hovercraft deck, the PTM shelter is anchored to the deck with chains. “Everything for the shelter fits in one 20-foot ISO container. It’s basically a building in a box,” says Banerjee. “You can put up the building with four people in about six hours with simple hand tools and without crane or forklift.”
In 2015, NexGen delivered a prototype shelter system, including panels, frames, doors, seats, lights, ventilation fans, electrical control panels and tools. It was deployed immediately and has served several missions, says Banerjee. NexGen received a production contract from the U.S. Navy last year for up to 10 shelters. The company delivered the first production shelter in March 2017 and is scheduled to deliver another one in October.
The panels, which are approximately 2 inches thick, feature balsa core and fiberglass phenolic facings and aluminum edges. They are produced using NexGen Composites’ proprietary vacuum assisted resin transfer molding (VARTM) process, then cured at temperatures ranging from 150 F to 220 F for several hours.
While constructing square panels may sound simple, they needed to meet several requirements. “The building is designed to take a very high load while traveling at up to 60 knots in high sea conditions, including waves coming over the bow and hitting the shelter,” says Banerjee. “Beyond the structural issues, the biggest challenge was ensuring the panels passed the fire test.”
The U.S. Navy requires a very high fire rating for its PTM shelters, so the shelter had to pass the ISO 9705 full-scale room corner fire test. Prior to that testing, NexGen did a lot of coupon level testing on 3 x 3-inch and 4 x 4-inch samples. “You can learn a lot from those tests about fire behavior, but there is no substitute for starting a full-blown fire in an 8 x 8 x 12-foot room and watching it burn,” says Banerjee.