By Carlos E. Lander
Header image courtesy of C. Lander
Carlos Lander was the distributor for Latin America for Cochran Undersea Technology.
Michael James Cochran, genius and founder of Cochran Undersea Technology, revolutionized the design of dive computers (DCs) with the company’s state of the art US Navy Computer that impacted the entire DC industry. But before exploring the accomplishments of Cochran Undersea Technology, let’s answer an integral question: “Who was Michael James Cochran?”
Mike was born in Daytona Beach, Florida, on May 21, 1941. He worked on a missile tracking ship as a young adult but also had an illustrious career in electronics, receiving 57 patents, including ones for the microprocessor and microcomputer chip.1 The microcomputer chip patent was assigned to Texas Instruments (TI)—where Mike worked for many years—and issued to Gary Boon and Michael J. Cochran in July 1971.
For his work on that microcomputer chip, Mike won an IR-100 Award from Industrial Research Magazine (now known as R&D World Magazine). After he left TI, he worked with NASA and invented a DC for their astronaut training program. He founded Cochran Undersea Technology in 1986, and began designing and manufacturing DCs for recreational, sport, commercial, and military diving applications.
In 2016, he was awarded the honorary position of Admiral in the Texas Navy, an accolade commending exceptional community service. In that same year, he won the New Orleans Grand Isle (NOGI) Award—frequently known as the Academy Award of Diving—which recognizes pioneers of the underwater world.
Sadly, Mike passed away on December 2, 2018, at the age of 77, leaving behind a lasting legacy of studies and research in electronics. Mike was always driven by passion—so much so that he worked until the end of his life, having never created a plan for Cochran Undersea Technology to continue without him.
The Cochran Undersea Technology employed brilliant and gifted people such as Martin Heerschap, designer and engineer for the Cochran closed circuit rebreather (CCR) and liaison to the US Navy throughout the Navy DC’s development. Sales manager and tech instructor Larry Elsevier was another who worked closely with Cochran clients including the US Navy and NATO. He passed away in 2014. There was also Jeff Loudan, physicist, mathematician, and software engineer; Stuart McNair, engineer; and John Corso, talented diver and the face of the company before Mike’s passing.
Creating An Advanced Dive Computer
Everything started in 1991 when Cochran Consulting Inc—the parent company to Cochran Undersea Technology—filed a patent for an “advanced dive computer,” which was intended to become an Oceanic air integrated DC.2 While that specific product was never patented, Cochran’s DC led to a huge advancement in the field. First, Mike made a DC from a Single Board Computer (SBC), and then he programmed everything in an “assembly language,” securing very high-speed, real-time calculations on a reliable DC.
An SBC refers to any computer that contains all of its components in one circuit board. This configuration is perfect for devices with limited hardware space, such as a DC. SBCs are self-contained and energy-efficient, important elements under diving conditions.
An assembly language is an architecture-specific, low-level programming language, and Mike used one to efficiently compile a very complex algorithm including a set of variables that, at the time, did not exist in a DC (breathing parameters being one).
The final product included a microprocessor, a depth and pressure transducer, an electrically conductive metal clasp, and other components that worked efficiently in a small package within a very low power consumption unit.
Consequently, Mike decided to produce his own line of DCs, dubbed Nemesis in the United States, and Aquanaut in the EU. Although the company worked with different brands, in the end they decided to concentrate on their own, the Cochran Dive Computer. No other manufacturer at the time designed and built every component of their DC in-house.
Cochran was the first company to produce a hoseless DC with the following design features:
- Mike’s design allows the main computer to be attached to the tank, so all the information gathered by the pressure transducer is transmitted to a diver’s wrist monitor (a second computer) in real time3, including the diver’s breathing parameters and workload. The wrist unit could be used independently as a DC in the event of a tank unit failure. Other brands used a transmitter attached to the tank, limiting the amount of information that could be sent to the main unit in short data bursts.
- As determined by Cochran, the cases on both units were air-filled (at 1 atm), ensuring that the cases were manufactured with material that was capable of withstanding extreme depths. Taking this approach required fewer case penetrations—such as buttons—and ensured an effective, long-term seal. In addition, the battery compartment was sealed from the electronics and built with materials that wouldn’t corrode. In an extremely rare case of flooding, the only damage would be to the battery compartment and not the electronics.
- The case was equipped with three electrically conductive metal clasps instead of pushbuttons. Those stainless contacts, in conjunction with the electronics, could detect the difference between saltwater and freshwater and thus refine the depth calculation. They could also distinguish metallic objects and fingers via electroconductivity.
- Another cool patented feature was the implementation of a vibration detector inside the unit which allowed the user to perform quick functions, like tapping the unit for five seconds to turn it on, or tapping it once to turn on the back light.
- The Cochran computer accurately measured and recorded the altitude (pressure) every minute whether it was on or off, accounting for minute changes of nitrogen levels in tissue.4
- Other contemporary DCs accounted for changes in decompression conservatism, and while some commercially available computers offered conservatism customizations, they didn’t provide adjustment calculation guidance. The majority of DCs based the conservatism factor in changing altitude; instead, Cochran used gas-loading to add conservatism in proportional increments so that divers both understood and controlled their conservatism.
- Cochran’s DC’s tandem PC software featured two capabilities not offered by any other manufacturer at the time. First, the PC software ran the same algorithm as the DC, behaving exactly as the DC did on a dive. Divers could perform a trial run on the PC graphically or review an existing profile. Secondly, divers could transfer gas loading and altitude characteristics from one DC unit into another DC unit. For example, if one computer malfunctioned, information would transfer from one unit to another. Therefore, divers could continue to dive with the new computer without noticing any difference.
- Perhaps most importantly, the Cochran DC never locked a diver out; most DCs would block access for 24 hours if the diver violated a stop. Cochran’s DC allowed them to continue their dive, and the DC would continue off-gassing at their current depth.
The Proprietary Cochran algorithm
Mike exchanged ideas with dive experts while developing Cochran’s proprietary algorithm, including Dr. Bill Stone, Dr. RW Bill Hamilton, and Capt. Edward Thalmann of the US Navy. He designed the circuit board with the algorithm in mind. During this period, Capt. Thalmann was developing the Navy’s proprietary VVAL18 algorithm with the intention of using it in a forthcoming Navy DC. His plan was to be able to test the DC on the manned test-dive data to evaluate its performance against the algorithm.
Once Cochran Undersea Technology was awarded the contract to build the Navy DC, they had access to all the scientific studies, probabilistic software, and anecdotal data on the installation of VVAL18 into a DC, which was pivotal to the development of Cochran’s own decompression algorithm. Cochran’s algorithm for the Nemesis included compensation for a bubble formation, and the Gemini—based on the Nemesis prototype—added variables for ascent rate and breathing parameters. The algorithm is based on a modification of Haldane’s decompression model, with compartments between five and 480 minutes.
There were several versions of the Cochran algorithm: 14, 16, and 20 compartment models. In the case of the 20 compartment version, the algorithm included fast compartments to compensate for helium gas and added a compensation for microbubbles related to ascent rate velocity. The model also used the same linear off-gassing from the Thalmann algorithm but included more than the fast compartment and ascent velocity to compensate for the aforementioned microbubble formations.
DC algorithm evaluation has been the subject of some research. For example, Dr. Carl Edmonds compared DC responses to a series of bounce dives. Dr. Karl E. Huggins used the same technique to evaluate DC algorithms by testing them on profiles that had known human subject results.
In his article published in 2004, Huggins notes that DC manufacturers did not validate their algorithms with human subject tests, so running a DC against a battery of previously tested dive profiles provided some rudimentary level of validation. So, when it came to validating their algorithm for use in both the Nemesis and Navy DCs, Cochran had the advantage of accessing the Navy’s database of man-tested dives.
Along with validation against the Navy’s database, the Cochran DC was validated against NOAA’s custom tables on the wreck of the USS Monitor, and the tables and DC were said to have matched well throughout the project.
In a 1989 Undersea and Hyperbaric Medical Society (UHMS) Workshop on Validation of Decompression Tables, UHMS determined that decompression algorithm validity could only be proven using primary data, such as results derived from controlled laboratory conditions. However, secondary data such as anecdotal performance reports could be cited as an operational evaluation but wouldn’t be considered proof of validity.
Cochran’s Navy DC and what made it so special
In 1996, there were no commercial DCs running the VVAL18 decompression algorithm. The US Navy Experimental Diving Unit (NEDU) sought a manufacturer to install the VVAL18 on a DC following their specifications, which were far from simple.
Cochran won the bid (being the only DC designer and manufacturer entirely in-house likely had much to do with it) and delivered five modified Commander DCs with the VVAL18 algorithm, which they called “Cochran Navy.” After a few modifications, Cochran developed additions to the Single Board Computer (SBC) that allowed for massive dive profiling memory and a one-second sample diving profile (the Navy required a maximum of two seconds). The finished product was a DC that handled large amounts of data and self-test diagnostics.
Due to the breathing parameters, the DC would operate with air if the depths were shallower than 23 m/75 ft, or at PPO2 = 0.7 (MK16 MOD 0 UBA) at further depths. Additionally, hands-free Gas Switching was implemented to eliminate the need for buttons5. Part of the computational power was required for this, as the switch function would depend on depth and time. Also, the DC was programmable on the surface or via PC.
The device computed decompression properly whether the diver was below or above the stipulated stop. The residual gas was based on the diver’s depth: a real-time-calculator, without gimmicks. Therefore, the DC never shut down or left the diver hanging. Other advances were handling of the magnetic signature, EMF emissions, and visible light emissions (red light) required for Explosive Ordnance Disposal (EOD) work, and for stealth. The DC could be programmed for the needs of the mission with the Navy’s Analyst computer software.
According to probabilistic decompression models for the profiles tested on the Cochran Navy DC, the average risk predicted of decompression sickness occurrence was low: less than 1%, as expected. Therefore, the DCs were validated by faithful replication of the decompression schedules when exposed to simulated manned tested-dives.
The computers made by Cochran Undersea Technology, while advanced for their time, were misunderstood and misused by many. Still, I consider Cochran’s Gemini DC the best ever made. If you’re not breathing from the back-gas and can reach certain pre-programmed depths, the computer automatically knows that you’re breathing from the deco bottle. If you start breathing from the back-gas again, automatically switching back without needing to push any buttons is an astounding characteristic unmatched by any other DC.
Unfortunately, the absence of a marketing division in the company gave Cochran the reputation of producing a military-only DC. The EMC-20H, a later DC, was also very advanced for its time, so it was sad to see Cochran vanish. I am comforted by the fact that I still have a few Cochran DCs I can use, and that they will serve me for many years to come.
I want to thank Martin and John for our conversations, and for their help in getting the facts straight.
- Patent No. 4074351
- Patent Nos. US4949072, 4999606
- Transmitting information every second reduces noise; the power transmitter and a 250 kilohertz frequency results in a strong communication between units and protection from interference with other devices such as camera strobes and scooter motors.
- When a diver changes from a lower altitude to a higher one, the computer detects this change and adds nitrogen to the tissue compartments. The differential pressure between the nitrogen in the body and the higher altitude must be equalized (outgassed). Conversely, when a diver changes from a higher altitude to a lower one, the computer detects this change and removes nitrogen from the tissue. The computer automatically reacts to long-term stays at a constant altitude. If a dive is made while at altitude (whether the computer has already automatically reacted or not), the nitrogen algorithm within the Dive Computer is adjusted depending on the exact depth.
- Patent No. 5794616
Cochran Undersea Technology Technical Papers:
Carlos Lander—I’m a father, a husband, and a diver. I’m a self-taught amateur archaeologist, programmer, and statistician. I think that the amateur has a different mind set than the professional and that this mindset can provide an advantage in the field. I studied economics at university. My website is Dive Immersion. You can sign up for my newsletter here.
InDEPTH’s Holiday Rebreather Guide 2023
Making a list. Checking it twice. Gonna find out which breathers are naughty or nice. That’s right! It’s time again for InDEPTH’s Holiday Rebreather Guide. This year, we are featuring 32 models of back, sidemount and chest mounted rebreathers, including five new units for your shopping enjoyment. So, get out your Pre-Buy Checklist, and that Gift Card (you do have a gift card don’t you?!?), and buy the breather of your dreams. Ho, ho, hose!
by Michael Menduno, Amanda White and Kenzie Potter. Holiday images by Jason Brown, BARDO CREATIVE.
A Guide to Backmount, Sidemount and Frontmount Rebreathers
6 Dec 2023 – Ho ho ho! InDEPTH’s Holiday Rebreather Guide continues to pick up steam (machines). This season we added Mares Horizon semi closed rebreather and Lombardi Undersea Research’s new RD1 back mounted oxygen rebreather. We also added Lungfish Dive Systems “Lungfish,” And iQSub Technologies’ new FX-CCR front mounted breather along with the Flex2 sidemount CCR. As such we believe the Guide is the most complete one on the market! Pst, pst Mr. Scammahorn, are you still there? Happy shopping divers! Ho ho hose!
Remember you can find all of the Rebreather Forum 4 presentations here on GUE.tv: REBREATHER FORUM 4
1 Dec 2022 – Ho ho ho! Once again, we have updated InDEPTH’s Holiday Rebreather Guide adding two new rebreathers; the new Gemini sidemount, needle valve mCCR from Fathom Systems, and the Generic Breathing Machine (GBM) front mounted, needle valve mCCR, with a dive computer-compatible, solid state oxygen sensor from Scubatron. We also updated the features on the Divesoft Liberty sidemount, and the JJ-CCR. This year, Vobster Marine Systems was acquired by UK-based NAMMU Tech, which plans to rename and re-issue a version of the VMS Redbare. See link below.
Finally, Innerspace Systems’ founder Leon Scamahorn agreed to work on getting us the needed information to add the storied Megalodon to the Guide. Scratch last year’s coal, Xmas cookies for you Mr. Scamahorn! Happy holidays shoppers, here is our updated rebreather guide! Mind those PO2s!
17 Dec 2021 – Ho Ho Ho! We have updated our Holiday Rebreather Guide with new rebreathers and updated features. Despite repeated requests, the only major closed circuit rebreather we are missing is Innerspace Systems’ Megalodon and its siblings. Tsk, tsk Leon Scamahorn, you’ve been a naughty boy! Behold, here is our updated guide. Mind those PO2s!
However, it took the fledgling tech community at least a decade to adapt mixed gas technology for open circuit scuba, including establishing the necessary supporting infrastructure, which was the first and necessary step in the move to rebreathers. A little more than a decade after Stone showcased FRED, British diving entrepreneur Martin Parker, managing director of then AP Valves, launched the “Buddy Inspiration,” the first production closed circuit rebreather designed specifically for sport divers, earning him the moniker, the “Henry Ford of Rebreathers.” [The brand name later became AP Diving] KISS Rebreathers followed a little more than a year later with its mechanical, closed circuit unit, now dubbed the KISS Classic. The rest as they say, is history, our history.
Today, though open-circuit mixed gas diving is still an important platform, rebreathers have become the tool of choice for deep, and long exploration dives. For good reason, with a greatly extended gas supply, near optimal decompression, thermal and weight advantages, bubble-free silence, and let’s not forget the cool factor, rebreathers enable tech divers to greatly extend their underwater envelope beyond the reach of open circuit technology.
As a result, divers now have an abundance of rebreather brands to choose from. Accordingly, we thought it fitting this holiday season to offer up this geeky guide for rebreather shoppers. Want to find out whose breathers are naughty or nice? Here is your chance.
Your Geeky Holiday Guide
The idea for this holiday guide was originally proposed to us by Divesoft’s U.S. General Manager Matěj Fischer. Thank you Matěj! Interestingly, it doesn’t appear to have been done before. Our goal was to include all major brands of closed circuit rebreathers in back mount and sidemount configuration in order to enable shoppers to make a detailed comparison. In that we have largely succeeded. We also included Halcyon Dive Systems’ semi-closed RB80 and more recent RBK sidemount unit, which are both being used successfully as exploration tools.
Absent are US-based Innerspace Systems, which makes the Megalodon and other models, as well as Submatix, based in Germany, which manufactures the Quantum and sidemount SMS 200, neither of which returned our communications. M3S, which makes the Titan, declined our invitation to participate, as they recently discontinued their TITAN CCR—they will be coming out with a replacement unit, the TITAN Phoenix CCR in the near future. We did not include the MARES Horizon, a semi-closed circuit rebreather that is aimed at recreational divers. No doubt, there may be brands we inadvertently missed. Our apologies. Contact us. We can update.
Update (22 Jul 2021) – French rebreather manufacturer M3S contacted us and sent us the specs for their updated chest-mounted Triton CCR, which are now included in the guide.
Update (9 Dec 2020) – Submatix contacted us and the Guide now contains their Quantum (back mount) and SMS 200 (sidemount) rebreathers. We were also contacted by Open Safety Equipment Ltd. and have added their Apocalypse back mounted mechanical closed circuit rebreather. We will add other units as they are presented to us by the vendors.
It’s The Concept, Stupid
The plan was to focus on the feature sets of the various rebreathers to provide an objective means to compare various units. But features by themselves do not a rebreather make. As Pieter Decoene, Operations Manager at rEvo Rebreathers, pointed out to me early on, every rebreather is based on “a concept,” that is more than just the sum of its features. That is to say that the inventors focused on specific problems or issues they deemed important in their designs; think rEvo’s dual scrubbers, Divesoft’s redundant electronics, or integration of open and closed circuit in the case of Dive Rite’s recently launched O2ptima Chest Mount. Shoppers, please consider that as you peruse the various offerings. My thanks to Pieter, who helped us identify and define key features and metrics that should be considered.
Though not every unit on the market has been third-party tested according to Conformitè Europëenne (CE) used for goods sold in the European Union, we decided to use CE test results for some of the common feature benchmarks such as the Work of Breathing (WOB), and scrubber duration. For vendors that do not have CE testing, we suggested that they use the figures that they publicize in their marketing materials and asked that they specify the source of the data if possible. As such, the guide serves as an imperfect comparison, but a comparison nonetheless.
Also, don’t be misled by single figures, like work of breathing or scrubber duration as they serve only as a kind of benchmark—there is typically a lot more behind them. For example, whether a rebreather is easy to breathe or not is a function of elastance, work of breathing (WOB) and hydrostatic imbalance. In order to pass CE, the unit must meet CE test requirements for all three issues in all positions from head down, to horizontal trim, to being in vertical position (Watch that trim!), to lying on your back looking upwards. It’s more difficult to pass the tests in some positions versus others, and some units do better in some positions than others.
The result is that some of the feature data, like WOB, is more nuanced than it appears at first glance. “The problem you have is people take one value (work of breathing for instance) and then buy the product based on that, but it just isn’t that simple an issue,” Martin Parker explained to me. “It’s like people buying a BCD based on the buoyancy; bigger is better, right? Wrong! It’s the ability of the BCD to hold air near your centre of gravity determines how the BC performs. With rebreathers you can have good work of breathing on a breathing machine only to find it completely ruined by it’s hydrostatic imbalance or elastance.”
Due to their design, sidemount rebreathers are generally not able to pass CE requirements in all positions. Consequently, almost all currently do not have CE certification; the T-Reb has a CE certification with exceptions. However, that does not necessarily mean that the units haven’t been third-party tested.
Note that the guide, which is organized alphabetically by manufacturer, contains the deets for each of their featured models. In addition, there are two master downloadable spreadsheets, one for back mounted units and one for sidemount. Lastly, I’d also like to give a shout out to British photog phenom Jason Brown and the BARDOCreative Team (Thank you Georgina!), for helping us inject a bit of the Xmas cheer into this geeky tech tome [For insiders: this was Rufus and Rey’s modeling debut!]. Ho, ho, hose!
With this background and requisite caveats, we are pleased to offer you our Rebreather Holiday Shoppers’ Guide. Happy Holidays!!
Note – Most prices shown below were specified by manufacturer before tax.
Download our two master spreadsheets, one for back mounted units and one for sidemount to compare rebreathers.
Special thanks to Amy LaSalle at GUE HQ for her help assembling the feature spreadsheets.
Michael Menduno is InDepth’s editor-in-chief and an award-winning reporter and technologist who has written about diving and diving technology for 30 years. He coined the term “technical diving.” His magazine aquaCORPS: The Journal for Technical Diving (1990-1996), helped usher tech diving into mainstream sports diving. He also produced the first Tek, EUROTek, and ASIATek conferences, and organized Rebreather Forums 1.0 and 2.0. Michael received the OZTEKMedia Excellence Award in 2011, the EUROTek Lifetime Achievement Award in 2012, and the TEKDive USA Media Award in 2018. In addition to his responsibilities at InDepth, Menduno is a contributing editor for DAN Europe’s Alert Diver magazine and X-Ray Magazine, a staff writer for DeeperBlue.com, and is on the board of the Historical Diving Society (USA)
Amanda White is the managing editor for InDepth. Her main passion in life is protecting the environment. Whether that means working to minimize her own footprint or working on a broader scale to protect wildlife, the oceans, and other bodies of water. She received her GUE Recreational Level 1 certificate in November 2016 and is ecstatic to begin her scuba diving journey. Amanda was a volunteer for Project Baseline for over a year as the communications lead during Baseline Explorer missions. Now she manages communication between Project Baseline and the public and works as the content and marketing manager for GUE. Amanda holds a Bachelor’s degree in Journalism, with an emphasis in Strategic Communications from the University of Nevada, Reno.
Kenzie Potter Stephens is a production artist for InDepth as well as part of the GUE marketing team. She earned her BS degree in Industrial Engineering and Marketing at the Karlsruhe Institute of Technology (KIT) in Germany, which assists her in using her multicultural upbringing to foster international growth within the community. In addition to her activities as a yoga teacher and an underwater rugby trainer, she has completed her GUE Tech 1 and Cave 1 training and is on her way to becoming a GUE instructor. Not letting any grass grow under her feet, she has also taken on a second major in biochemistry in order to create a deeper understanding of our planet’s unique ecosystems as well as the effect of diving on human physiology.