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Excerpted from The History of Oilfield Diving: An Industrial Adventure
by Christopher Swann (Oceanaut Press)
by Christopher Swann (Oceanaut Press)
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One of Dan Wilson's responsibilities after the sale of General Offshore Divers to Union Carbide was to build the Purisima diving bell, the artist's conception of which he had shown to Ed Link in Washington D.C. in September 1963. In designing the Purisima, Wilson was well aware that the competitive advantage he had gained with helium would not last long. By putting the diver next to the work in a lock-out bell he would increase the efficiency and safety of deep-water operations, and thereby maintain his edge. Furthermore, assuming the work in California increased as expected, there could well be a shortage of divers—which meant heavy gear divers.
The risk from Wilson's point of view as an employer was that the divers would be able to dictate their wages. The only alternatives to heavy gear divers were light-gear abalone divers and sport scuba divers. Unlike the Gulf of Mexico, where most of the diving was relatively shallow and the water generally warm, the work in California was too deep and the water too cold to make diving with a surface-supplied mask and wet suit an option. Scuba, except for certain isolated tasks, was unsuited to the oilfields and there were in any case very few scuba divers with the necessary background. If, however, as Wilson expected, the future of deep diving lay in using light gear out of bells, he had a large pool of divers he could bring in from the abalone fishery.
To understand why Wilson designed the Purisima as he did, it is necessary to look at how General Offshore Divers were operating at the time and how they expected to operate in the immediate future. As mentioned before, most of the work lay in the 250'/76M range, with bottom times held to one hour. In the first year or so, the company made 72 dives without having to send down a second diver to finish the job.
“A general dive philosophy we used at the time was that if you couldn't finish the job in one hour you weren't rigged properly," said Wilson.
Even on the first subsea tie-ins, two or three dives a day interspersed with surface rigging and welding were usually sufficient. Given the relatively modest bottom times the typical job required, Wilson saw no need to consider saturation diving, which would have entailed building a surface decompression chamber with a mating flange. Although Wilson designed the Purisima for 1,000'/304M, he did not expect to work deeper than 400'/122M, where the decompression times would be short enough that the divers could reasonably decompress in the bell. One should also note that Wilson thought it would be possible to shorten decompression by using different gases in sequence or in combination, or both, much as Hannes Keller had done. Moreover, one of the reasons he had sold to Union Carbide was to gain access to the Linde Division's extensive research into gases.
The Purisima’s principal characteristic was its double-sphere configuration. Wilson thought it would be advantageous if the diving supervisor, alone or with the oil company representative responsible for the work, could observe and direct the diver on the bottom. The diver and tender would be in the lower sphere, the observers in the upper sphere. The bell would descend at atmospheric pressure, with the hatches between the spheres open. Wilson designed the bell so that all the hatches lined up, to provide the option of using the bell horizontally as a submarine hull at a later date.
On the bottom, the diver and supervisor would go over the job, then the tender would winch the top hatch of the lower sphere closed and pressurize the compartment. When the internal pressure equaled the external pressure, the outer bottom hatch would open and the diver would go out. Throughout, the occupant or occupants of the upper sphere were to remain at atmospheric pressure. At the end of the dive the tender would close the bottom hatches and start decompression as the bell was lifted to the surface. Once on deck, those in the upper sphere would leave the bell through the two top hatches. Alternatively, if the work required this, the bell could descend with a diver and tender in each sphere. At the end of the first team's dive, the crews would change places, the team from the lower sphere starting their decompression as soon as they had transferred.
Before the sale to Union Carbide and General Precision, Wilson had set up a separate company, Deep Submergence Systems, to build the Purisima. When Lad Handelman and Whitey Stefens decided not to participate in the venture, Wilson invited Jon Lindbergh, the eldest son of Charles Lindbergh, who had joined General Offshore after running his own diving company in San Diego, to be his partner.
Lindbergh was shy almost to the point of being reclusive; but he was determined and far-sighted (he once, correctly, told a group of dyed-in-the-wool heavy gear divers that the helmet of the future would look like a motorcycle helmet) and he provided two things Wilson needed. The first was a fresh perspective. The second was money—of which Wilson, who was still paying off the $25,000 debt of his old abalone business, was woefully short. At the time of the sale, Deep Submergence Systems became part of Ocean Systems with General Offshore Divers and the equipment company.
Wilson and Lindbergh took the drawing of the Purisima, which Wilson filed as a patent application in February 1964, to Jon Borg, an engineer in Santa Barbara. One of the first questions was how big to make the hatches. To find out, Borg cut out various sized cardboard rings, which Wilson and Lindbergh slid over their shoulders. The diameter that allowed comfortable passage with a little to spare would be the hatch size. Wilson and Lindbergh were very thin, however; furthermore, they failed to take into account that the diver would be unable to bend going through the entrance trunk. This was to have unintended consequences when other diving companies built their own bells and many copied the hatch size of the Purisima.
“Unless you were a skinny guy,” Wilson observed,“you could hardly get in and out of the average hatch.”
There were numerous other technical challenges: buoyancy control, the design of the windows, a drop-weight system for emergency ascent, carbon dioxide scrubbers and an umbilical to supply the bell with power and breathing gas. The manifold box and communications would be little different from what the company used for surface diving.
Wilson constructed the bell of mild steel hemispheres formed by hot spinning. Although the process ensured good control over sphericity, it proved impossible to control the thickness at the poles and the equators. Consequently the spheres were much heavier than intended, with the result that the bell sank even without the counter-weight, making it necessary to add a third sphere on top for flotation—which doubled as an emergency gas supply. This third sphere was to make launch and recovery of what was already a large bell even more awkward than it would otherwise have been.
Continued in the next post
