Deep dive

I am still catching up on the technical details that are trickling out of the deep-sea dive feat that James Cameron and crew pulled off in the Challenger Deep, Mariana Trench last week. As a structural engineer, the obvious object of my fascination is the dive submersible, Deepsea Challenger. Not just withstanding, but to be fully operational under 1137bar external hydrostatic pressure at 10.898km below sea surface is absolute insanity! Just to give you an order of magnitude, a 10bar impulse blast overpressure is all it takes a high strength steel structure to be crushed beyond recognition. Which is why I find this following incredibly fascinating:

About 70 percent of the sub’s volume is taken up by syntactic foam. Formed of millions of hollow glass microspheres suspended in an epoxy resin, syntactic foam is the only flotation material that can stand up to the incredible pressures in the deep ocean. But when the engineers behind the DEEPSEA CHALLENGER tested the two “full-ocean-depth-rated” foams that were on the market, they proved not to be adequate. In fact they cracked, warped, and compressed, losing buoyancy, and did not have nearly the tensile strength required for the new vehicle to operate under extreme conditions. This was a serious setback to the project. But lead engineer Ron Allum then spent 18 months designing a new type of syntactic foam, which has since been dubbed ISOFLOAT and patented. The foam provides the buoyancy James Cameron needs 7 miles (11 kilometres) down, without crushing or warping, and has twice the tensile strength of previous foams, allowing it to be used as the main structural frame of the sub.

The point really is not just its hull, but every exposed element, including its propellers, its lighting, mechanical arms, the connections, all experience this crushing pressure! Making them work under it is some frontier engineering indeed.1

  1. PDF: ‘The Finite Elements team used ANSYS Mechanical software to design a geometrically complex capsule that can withstand pressures of 16,500 pounds per square inch (114 megapascals, or MPa), 1,100 times the pressure at sea level.’