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Confronting the Unknowns of Decompression with the First Electronic Rebreather

How did Electrolung inventor Walter Starck and his cronies decompress from dives to 100m/326 ft before the advent of dive computers or even constant PO2 tables? Dr. Starck explains his procedures and rationale. Deep stops anyone?

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by Walter Starck
Photos courtesy of Walter Starck

The design and manufacture of the first commercially available, electronically regulated closed circuit mixed gas rebreather in 1968 presented a multitude of problems to be solved in the design and manufacture of the device itself.  Successful development and production of the Electrolung presented an additional problem. Decompression tables were limited, and none were available for a constant partial pressure of O2 with a varying percentage of inert gas as occurs in an electronic rebreather. The US Navy tables were the only heliox tables readily available. Those used in the offshore oil industry were all treated as commercial secrets by the offshore diving companies. Decompression computers had not yet been invented. 

To start with, I interpolated from the US Navy helium tables for an equivalent partial pressure depth for the Electrolung.  Although, by today’s standards, this may seem unacceptably risky, it was less so than may appear. If immediate recompression is available at the first symptoms of any decompression sickness, progression to more serious levels is rare. When recompression is delayed for several hours, or more, to get to a chamber there is a high probability of increasing tissue damage requiring extended treatment and lengthy recovery or permanent impairment. 

A young Walter Starck about to dive in the Coral Sea with his Electrolung in 1971.

My research vessel, El Torito, was equipped with a large (42’’ x 12’) double lock recompression chamber which could comfortably accommodate two persons, or even three if needed. The inner lock was kept pressurized to 30 m/100 ft, so getting to 18 m/60 ft of pressure could be accomplished in less than a minute by just getting in, closing the outer door, and opening a valve to let the main inner chamber equalize with the entrance chamber. An oxygen rebreather also provided for 100% O2 decompression without the fire risk of pressurising the chamber with O2. Having a chamber immediately available reduced the risk of experimenting with decompression profiles to an acceptable level. In practice, there was only one incident where the chamber was needed, and that involved pushing the limits with a repetitive dive to 60 m/200 ft with only an hour surface interval.

While getting into the matter of decompression, I came across an interesting study by the Australian physiologist Brian Hill, who found that the pearl diving industry in northern Australia had developed (by trial and error, including numerous fatalities) a mode of decompression that started deeper, ascended slower, and ended deeper but was faster overall.  Based on this, some relevant physics, and Hill’s own extensive lab work, he proposed a theory of what he called thermodynamic decompression. In this regard, he believed that the idea of avoiding bubble formation by keeping within a hypothetical limit of supersaturation is incorrect, as any degree of supersaturation results in a gas phase beginning to form as a thin film at tissue surfaces, which then begin to coalesce into sub-symptomatic bubbles.



In his view, the conventional tables were generating sub-symptomatic bends by allowing divers to ascend too quickly and then having to spend a lot of (decompression) time to prevent them from growing into symptomatic bends. If the bubble formation is avoided to begin with by allowing the inert gas to escape through the dissolved gas saturation window provided by the ability of tissues to metabolize O2, decompression can be optimized. 

Diver with Electrolung.  Note pink Baralyme absorbent.  The acrylic bubble was being used for a shark cage.

My study of his material left me with the impression that it was well founded, so I began to titrate decompression toward that direction. This led into a series of 92 m/300 ft dives with 15 minutes descent and bottom time, a slow 10 m/30 ft-per-minute or slower ascent time, a couple of stops for about two minutes at around 46 m/150 ft and 22 m/75 ft, finishing with 15 minutes on pure O2 at 10 m/30 ft. On different occasions, but not at the same time, three other individuals accompanied me, all without DCS in some 30 such dives.

The effort, resources, liability risk, and limited economic potential involved in endeavouring to develop a full set of tables of this kind, as well as my own prime interests in marine science and exploration, ruled against further pursuit in this direction. However, a few years later when I arrived in Australia with El Torito, I got in touch with Brian Hills and had the opportunity to spend several days with him in Adelaide.  He went on to a distinguished career in decompression physiology at several institutions in the US and UK. 

See accompanying Story: Electrolung: The First Mixed Gas Rebreather Was Available to Sport Divers in 1968

Dive Deeper:

For more on Hills and his thermodynamic theory, see: Brian Andrew Hills 

Wikipedia: The US Navy’s Thalmann Constant PO2 Algorithm

NEDU: DEVELOPMENT AND VALIDATION OF 1.3 ATA P02-in-He DECOMPRESSION TABLES FOR THE MK16MOD1 UBA

InDepth (Four part series): Decompression, Deep Stops and the Pursuit of Precision in a Complex World by Jarrod Jablonski

UHMS: PROCEEDINGS: DECOMPRESSION AND THE DEEP STOP (2008)

Immersed: The International Technical Diving Magazine (Winter 1998), Starck, Walter 1998. In Water Recompression: Problem or Solution? by Walter Starck. Reprinted courtesy of DIVER mag.

InDepth: A New Look at In-Water Recompression (IWR) 


Walter Starck is one of the pioneers in the scientific investigation of coral reefs. He grew up in the Florida Keys and received a PhD in marine science from the University of Miami in 1964. Since 1978, his home has been in north Queensland, Australia. Throughout his career in marine biology, participating in expeditions around the world,  Dr. Starck has been extensively involved with development of the technology required to facilitate his activities. In several instances patented inventions and commercial products have resulted. In addition to the optical dome port and the Electrolung other noteworthy achievements in this area have been: The Bang stick—a hermetically sealed underwater firearm for hunting and defense, underwater housings for numerous cameras and instruments, underwater lighting systems, a multipurpose commercial waterproof electrical connector,  design of the unique research vessel El Torito, a 9 meter high-speed diving launch, a 24 passenger eco-tourism vessel, and the Oceanic 8000 Longboat.  The longboat was a long narrow high efficiency powerboat inspired by the efficiency of the log canoes of the Solomon Islands.  He has also built and flown an amphibious aircraft of advanced canard wing design using high technology composite materials. Recently (Aug 2017) he was senior author on an extensive update on the Alligator Reef study that brought the total species list for that locality up to 618 species.

Dr. Starck has authored over 100 articles and books, which include numerous technical and peer reviewed scientific studies as well as many articles in leading popular publications. His photography has been widely published in conjunction with his writing, and he has produced nearly 20 films and videos. Throughout his extensive career, he has managed to inspire not only admiration, but also the ire of some detractors who have taken umbrage at his efforts to inject what he believes to be “a rational perspective on human ecology into the eco-mania that has become epidemic in our struggling Western economies.” His criticisms of the “poor science and blatantly false claims widely used to support various environmental agendas” have earned him some criticism.

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Getting to the Bottom of the HMS Regent Mystery

Italian shipwreck explorer Fabio Bisciotti and his team have reportedly solved the mystery of the HMS Regent, one of four Rainbow-class submarines built for the Royal Navy, that was lost at sea during WWII and discovered 50 years later near the Puglia region of Italy. Au contraire! Bisciotti et al, have now identified the wreck as that of the Italian sub Giovanni Bausan, and subsequently located what appears to be the remains of the Regent near the port of Brindisi. InDEPTH managing editor Ashley Stewart reached out to Biscotti to get the deets.

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By Ashley Stewart. Images courtesy of Fabio Bisciotti and Michele Favaron.

The HMS Regent, one of four Rainbow-class submarines built for the Royal Navy, patrolled during World War II until she was lost at sea sometime in April 1943. 

There would be no news of the submarine for more than 50 years, until a research team proclaimed to have found the wreck in the Apulia region of Italy. But the Regent was lost once more when the site was declared by another team, including Italian explorer Fabio Giuseppe Bisciotti, to be instead a former Italian submarine once called the Giovanni Bausan.

Now, Bisciotti believes his team has solved the mystery of the HMS Regent once and for all, discovering a wreck with similar characteristics near the port of Brindisi. InDEPTH spoke with Bisciotti about the discovery and why he believes he’s found the wreck of the HMS Regent. Bisciotti previously spoke to InDEPTH about finding a sunken German WWII aircraft in the South Adriatic Sea. Edited for length and clarity.


Bisciotti’s report: English, Italian (Original)


How did your search for the HMS Regent begin?

We know during the war many submarines from the United Kingdom were lost here in the Adriatic Sea. From some combat diaries about some skirmishes in this area, we know we have various wrecks including submarines and one of them is the HMS Regent. We started this research with a unique objective to know the truth about this wreck.

Many years ago, a research team believed they found the HMS Regent. But after our research, we discovered it was an error. The previous research team believed they found the Regent in an area much farther north in the Apulia region in the Barleta area. The wreck in this area is not the HMS Regent but a former Italian submarine called the Giovanni Bausan. It was used after the arrival of allies in the south of Italy as an oil depot, renamed GR 251, without a conning tower or propellers, transformed into a big warehouse. We have documents from the National Archives in London that show American allies sunk this wreck in the same region.

How did you discover the wreck you now believe is the Regent?

We started developing some research and arrived in the real area where we believed the Regent was lost, quite south near the port of Brindisi. Thanks to the fisherman of the area and old witnesses, we discovered a story. 

Here, in the late afternoon on the 18th of April of 1943 — the exact day when the Regent was lost — in front of the seashore, it was heard a very big explosion. The next day, some oil and fuel formed four or five miles out in the open sea where it was believed a submarine hit a mine. By the reports of the Italian Coast Guard of that time, the bodies of four sailors were found in the days after the accident. The first was found in an area nearby Brindisi. A second body was found in the Missipezza area south or Brindisi, and two other bodies were found in the Otranto and Castro Marina areas. The bodies were found between eight and 25 days after the accident. You can imagine the condition of these poor guys, but it is believed one was a non-commissioned officer and the other three were simple sailors. They were surely submariners due to their uniforms, which were blue as British submariners.

After much time, we narrowed down the area thanks to the local fisherman, and found a very object in the water around 80 meters down. The area is quite dangerous due to quite strong drift, and the direction of the wind from the area would create the correct route to where the bodies were found.

Why do you believe this wreck is, in fact, the HMS Regent?

We found some particular points unique to British submarines. First of all, the hull of the wreck had the particular dimension and measurement that pointed to British design. Then, we arrived at the bow. The bow is of course upside down, but we found the area where the torpedo tubes were located. We found three on each side. Everybody knows, or at least wreck divers know, the bow section of a British submarine is unique in its class. A British submarine has a total of six torp tubes, instead of four like a German U-boat or Italian submarine. 

But, in the center of the wreck, it’s gutted and open. We are sure there were two explosions. The first explosion by a mine, on the left side, and a second explosion probably detonated by the ammunition store. Of the wreck’s 87 meters in length, the visible part is about 65 meters and the rest is under the mud. We were not lucky with the visibility and extensive damage, so we have small proofs but enough to say for sure this is a British R-Class submarine.

Tell us about the dive itself.

The diving operation was with two boats and the dive team, Michele Favaron, Stefania Bellesso, both of Acquelibere Sub Padova, and myself, with research from Giuseppe Iacomino, in partnership with the Italian Naval League. We arrived on the point  in the very early morning with my personal boat with Garmin. We already knew the wreck was there by previous scan. We set a lazy line on the seabed to mark the position. We prepared our equipment and cameras. The current was very, very, very strong. It’s not an easy dive, it’s very hard. It was hard to stay on the line but when we arrived on the wreck, the conditions were better and visibility was good. The wreck lies in about 75 meters/245 ft on the seabed, but the shallower part is at 57 meters186 ft. The dive was on open-circuit with 18-45 trimix as back gas, and 50% and 100% deco gasses. About 25 minutes bottom time and 45 minutes deco.

What’s next for your team?

We are involved with the Pentagon in the finding of some U.S. bombers ditched in the Adriatic sea and the finding of still-missing submarines nearby. We are also working with a university on the study and the maintenance of present wrecks and future projects. 

Fabio and his team published an extensive report about the discovery with the help of the Italian Naval League, which provided logistical support. Here’s an excerpt describing the dive:

“Operation N 41 has finally come to an end, the scout ENDURANCE sailed from Manfredonia on 20/05/2022 at 9.30 am to Villanova arrives on site at 15.00. The team, made up of Fabio Giuseppe Bisciotti and Giuseppe Iacomino immediately returned to the sea towards the REGENT point, thus ensuring the planned dive point for the following day. The diving team, composed of Michele Favaron, Stefania Bellesso and Fabio Giuseppe Bisciotti reached the diving point at 7.15 UTC +1. At the moment of the descent there is immediately a very strong cross current such as to force the team to use the treadmill line in order not to lose energy.

Touchdown of the wreck at an altitude of -60 meters where it was found that the body appears to be overturned by 180 with the rostrum cutting cables along the entire keel clearly visible.

The protuberance noted and photographed undoubtedly has the function of a cable-cutting rostrum. The design is typically English of R-CLASS  as the height of this rostrum is 11.5 inches, or 30 cm appropriately calculated with line. The entire body of the wreck has been shaped and the total length is 87 meters, which is the length of a R-CLASS submarine. The remaining models such as classes P, T, S, and U do not possess such dimensions (P) or design (T, S, U) such that they can be traced back to the rostrum studied. The photo taken at the stern shows exactly the rostrum and is completely identical to the drawing of the construction plans. Please note that only the R-CLASS possesses these characteristics. At the height of the gutted point, the rostrum appears strongly deformed due to the violent explosion of the mine.

The ovals shown in the photo do not belong to the turret as you might think but refer to the lower ventral band of the hull in the area between the waste oil recovery and batteries n. 2 and n. 3, exactly below the engine pistons. By looking in the construction plans they are easily identifiable and have been found exactly in the same area. As a first impression the HMS REGENT struck a mine on the left side which undoubtedly initiated a second detonation below the casemate of the 122 mm gun. The explosion did not disable the submarine but literally gutted it.

Currently, the possibility of penetration inside the wreck is excluded due to the structural impossibility of ensuring easy entry and exit. Further studies will be started later for the safety of the wreck itself.”

DIVE DEEPER

Operation Regent-Bausan Report by Fabio Bisciotti

Rapporto Regent-Bausan (Italian) by Fabio Bisciotti

InDEPTH: Surveying and Identifying a Sunken JU 88a German WWII Aircraft (2019) by Fabio Biscotti


InDepth Managing Editor Ashley Stewart is a Seattle-based journalist and tech diver. Ashley started diving with Global Underwater Explorers and writing for InDepth in 2021. She is a GUE Tech 2 and CCR1 diver and on her way to becoming an instructor. In her day job, Ashley is an investigative journalist reporting on technology companies. She can be reached at: ashley@gue.com

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