CompositesWorld
Issue link: https://cw.epubxp.com/i/841219
JULY 2017 44 CompositesWorld FOCUS ON DESIGN Composite submersibles: Under pressure in deep, deep waters Manned deepsea exploration calls for a highly engineered solution that, at 6,500-psi service pressure, will maintain buoyancy and preserve life. » Even as massive amounts of money, energy and attention are being paid to the development of privately funded launch and delivery systems for space exploration — and the application of composites therein — an environment much closer to home is, despite its proximity, as remote and difficult in its own way to access and study. At an average depth of about 3,810m, with a maximum depth, at Challenger Deep in the Pacific, of 10,916m, the world's oceans offer a formidable challenge to explorers. Scientists, marine biologists or oil and gas engineers and others who would dive to such depths require a vessel that can withstand deepsea water pressure that, at the 3,810m average, is a massive 5,551 psi or 378 atmospheres. Such vessels, called submersibles, offer capacity for three to five occupants, can explore depths from 1,200m to 6,500m, provide a viewing porthole or portholes, and are equipped with lighting systems and cameras. Conventional submersibles feature steel, aluminum or titanium hulls. Metallic hulls, however, because they are not buoyant in designs for depths of more than 2,000m, present challenges when it comes to managing ballast for ascent and descent. In particular, metal- hulled craft require the use of syntactic foam attached to the outside of the craft to achieve neutral buoyancy. In 2014, submersibles manufacturer OceanGate Inc. (Seattle, WA, US) was coming off the successful launch of Cyclops 1, its steel-hulled, five-person craft, rated for underwater exploration to a depth of 500m. e company was set to embark on development of Cyclops 2, a five-person research-class submersible, designed for a maximum depth of 4,000m. OceanGate CEO Stockton Rush says the company had been evaluating the potential of using a carbon fiber composite hull since 2010, primarily because it permits creation of a pressure vessel that is naturally buoyant and, therefore, would enable OceanGate to forgo the use — and the significant expense — of syntactic foam on its exterior. So, for Cyclops 2, OceanGate decided to avoid the metallic hull altogether and began a search for a manufacturer that could help it develop a composite hull. It is believed that the first time carbon fiber composites were applied to the hull of a deep-diving, manned submersible was for the one-person DeepFlight Challenger, commissioned by adven- turist Steve Fossett in 2000 for a dive to the bottom of Challenger Deep (see Learn More, p. 47). Designed and built by famed marine engineer and submersible designer Graham Hawkes, a principal at the time of Hawkes Ocean Technologies (Point Richmond, CA, US), it featured a cylindrical carbon fiber/epoxy composite hull with 6-inch-thick walls. It was nearing completion in 2007 when Fossett was killed in a light-aircraft crash. e Challenger was subsequently sold, and has yet to be fully tested or deployed in By Jeff Sloan / Editor-in-Chief A deepea submersible "first" Rated for ocean depths to 4,000m, OceanGate's (Seattle, WA, US) Cyclops 2 five-person submersible features the submersible industry's first commercial carbon fiber composite hull, designed and manufactured by Spencer Composites (Sacramento, CA, US). Source (all photos) | OceanGate