OceanOpportunity
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Hey all - havent been here to Scubaboard in a million years, but happy to answer some questions on RD1 etc.
First, and most importantly, a rebreather is a rebreather is a rebreather. I've been trained on 3, have dived 8 extensively (>1000 hrs) including over a dozen sub-400' dives with custom mods, have built numerous custom systems, and am now bringing the RD1 unit to market. They're all tools for a job, and while there is benefit for everyday diving, very VERY few people are realizing rebreather's fullest benefits.
The RD1 development project got me thinking a bit differently, towards helping them be more fully realized, and it all started in very shallow water, digging clams of all things. Before working through production components, I spent 3 seasons diving prototypes -everyday- for 3-5 hours throughout our summer season, all in less than 20 feet of water. Through that, I completely retaught myself how to dive a rebreather, and now believe very strongly that this is the best starting point. The industry has done a disservice in suggesting that rebreathers are all about deeper, longer, harder with technical diving...it's just not so.
In shallow water, one can learn all the skills needed to manage a breathing loop, dial in buoyancy, and become better in tune with the rebreathing mindset. After learning with a hard floor in the shallows, it becomes obvious to the student what needs to happen to start extending depth - the intuition (and fear) guides the way towards 'diluting' the atmosphere, and then off you go - it becomes very, very easy to understand. From my experience with students, the eureka moment comes after 20 or so hours in shallow water. By then the mechanics are figured out, you can appreciate doing long 3-5 hour length dives, and the physics becomes acutely clear. I honestly dont think I'll ever teach someone on a mix unit first ever again.
From a design standpoint, I engineered RD1 around a 5 hour capability. The scrubber has tested out at well in excess of that under certain controls, and is matched with a 13cft O2 cylinder (368liters). So, at a 1slpm consumption rate, that's 6 hours of O2 - plenty and then some. Under most operating conditions, 5 hours is a conservative limit for this unit. This number is significant since the REPEX oxygen limits allow for 5 hours of diving at a pO2 of 1.0 bar without penalty over multiple days. So, load up and go dive 5 hours day in and day out and you'll quickly realize how much has been missing from your everyday diving.
When converting RD1 to a mCCR, which several have, the onboard air cylinder (which was just bailout/inflation) becomes air diluent. I still dive to 1.0 bar, allowing 5 hrs a day, and with very little concern for oxygen toxicity. This is a new approach for me and strays from the norm a bit. Historically, nitrox and technical diving has always been about boosting O2 to speed up decompression and get out of the water quicker. By contrast, with a rebreather, we have nothing but time, so reduce the pO2 and start doing long dives. I can say from firsthand experience that even on deep mix dives 1.0 versus 1.2/3 on the bottom doesnt amount to much difference in decompression.
From a training/practical standpoint, flush the unit with O2 at surface (1.0, just like we do diving as an O2 only unit), then drop to 20fsw and voila - you should be at 1.6bar thanks to easy math. Carry on with your descent, diluting as you go, and ride the 1.0 bubble +/- which is very easy with a leaky valve and bypass button. On ascent, do the reverse - flush O2 at 20fsw to see 1.6. This wont last since you're offgassing into the loop, but its good practice, then when you surface you're back to 1.0.
I dive the stock RD1 this time of year multiple times a week, and with a pO2 display, wont hesitate to dive it to 30-40-even 50 feet in certain circumstances (in its stock configuration). This year Ive added an air manual add valve which will make the deeper end of this range a little more routine. Theres often a misunderstanding about O2 only units that you will combust at 20' - it's just not so. Even at 1.6bar, there is a very conservative dosing limit of 45 minutes. When adding a pO2 monitor, you learn quickly that its near impossible to actually dive with 100% O2, and can learn to work that to your advantage for routine depth excursions to 30 feet without any issue at all. I'd say the majority of the time a shallow dive will ride from 0.7 to 1.3bar, voila again - the 'bubble' to ride on an mCCR dive down the road.
On training - come on up - training is a day and a half, or one day for a try dive. Those seeking little plastic cards are out of luck for the moment. We do have some instructors working on programs with their agency of choice, which may roll out in the next 12 months. Unfortunately, the rec industry 'standards' are all built around jumping in to mixed gas units, so it's not an easy alignment to offer a precursor to that. I also anticipate some resistance since learning O2 only up-ends alot of work done recently by others - the entire paradigm can be restructured for earlier career adoption (where it should be), and shortened paths through mixed gas diving that actually align with physiology rather than arbitrary depths/durations to print on cards.
