Sphere

240px-Sphere-wireframe.png
Sure Sphere is a filthy piece of literary swill but it also a vital component of any submersible. As you may remember from geometry, for any given volume, a sphere has the smallest surface area, or for any given surface area, a sphere will have the greatest volume. From a practical standpoint for a deep-sea submersible, this means less surface for pressure to act upon. Thus the choice for the ‘large’ compartment to hold humans on a deep diving submersible is a sphere.


cigarc.jpgThe first deep-diving sphere was the aptly named Bathysphere of Barton and Beebe, making its first unmanned test in 1930.

The Bathysphere was made by the Watson Stillman Hydraulic Machinery Company in Roselle, New Jersey. Made of cast iron, it could hold two people. The “walls” measured one and a half feet thick and were made of a single casting of the finest open-hearth steel. The Bathysphere and its cables cost Barton $12,000.

300px-Bathyscaphe_Trieste.jpg
The deepest diving sphere was the one that hung below float filled chamber filled with gasoline. In 1960 the Trieste bathyscaphe descended to 10,900m in the Mariana Trench. Big enough to hold just to people

The pressure sphere was built by the Krupp Steel Works of Essen, Germany, in three finely-machined sections (an equatorial ring and two caps). To withstand the high pressure of 1.25 metric tons per cm² (110 MPa) at the bottom of Challenger Deep, the sphere’s walls were 12.7 cm (5 inches) thick (it was overdesigned to withstand considerably more than the rated pressure). The sphere weighed 13 metric tons in air and 8 in water (giving it an average specific gravity of 13/(13-8) = 2.6 times that of sea water). The float was necessary because the sphere was dense: it was not possible to design a sphere large enough to hold a man which would withstand the necessary pressures, yet also have metal walls thin enough for the sphere to be neutrally-buoyant.

jsl_front_midw_600.jpg

Modern spheres are a whole other ballgame. Harbor Branch Oceanographic Institutes’s submersible contains a solid acrylic sphere allowing scientists exceptional views. These views come with a price as it limits the Johnson-Sea-Link to less relatively shallow depths (>1500m). The more familiar Alvin, soon to be replaced, possesses a titanium sphere. As you can see from the figure below, the sphere rests forward and most of the external shell of the Alvin contains ballast and syntactic foam to regulate buoyancy. The sphere in modern submersibles can be released from the rest of the body in emergency situations to return to the surface. Jim Richardson as a thorough and excellent writeup with pictures at NavSource Online about another Alvin Class submersible the Sea Cliff (DSV-4). Included is some wonderful photos of the entire construction process.

AlvinDiagramOfSub.jpg

Dr. M (1801 Posts)

Craig McClain is the Executive Director of the Lousiana University Marine Consortium. He has conducted deep-sea research for 20 years and published over 50 papers in the area. He has participated in and led dozens of oceanographic expeditions taken him to the Antarctic and the most remote regions of the Pacific and Atlantic. Craig’s research focuses on how energy drives the biology of marine invertebrates from individuals to ecosystems, specifically, seeking to uncover how organisms are adapted to different levels of carbon availability, i.e. food, and how this determines the kinds and number of species in different parts of the oceans. Additionally, Craig is obsessed with the size of things. Sometimes this translated into actually scientific research. Craig’s research has been featured on National Public Radio, Discovery Channel, Fox News, National Geographic and ABC News. In addition to his scientific research, Craig also advocates the need for scientists to connect with the public and is the founder and chief editor of the acclaimed Deep-Sea News (http://deepseanews.com/), a popular ocean-themed blog that has won numerous awards. His writing has been featured in Cosmos, Science Illustrated, American Scientist, Wired, Mental Floss, and the Open Lab: The Best Science Writing on the Web.