Maximum SAC for Tech diving?

[BeijaFlor]

I'm certified as a recreational diver, NAUI advanced with SSI Nitrox and PADI Sidemount/Wreck/Deep.

I recognize that I'm an air-hog, but I haven't done much (or rather, quite enough) to establish my SAC rate. Some dives, I've recorded my SPG pressures at the beginning and end ... other dives, I've neglected it. Admittedly, my next project on my next diving vacation is to record it, to calculate it, to nail it down.

My question is -- what SAC rate is acceptable, for tech-diving training?

I've done a fair amount of "deep" diving, i.e. deeper than 30 meters. I've had a few dives where my computer --a Suunto Zoop, programmed for what is possibly the most conservative algorithm used in dive computers today -- went into mandatory-deco mode. Yes, I acknowledge that Ol' Debbil Deco is the Original Deadly Sin, that must be Disavowed by any Recreational Diver ... but I dealt with it, as I had to, and on surfacing I was assured by my dive-guide that I was worse at 'rock, paper, scissors' than I was at deco-avoidance.

I'd like to have the option of spending more time on the deep wrecks, for example the Japanese DC-3 "Tabby" wreck that lies at 140 feet (43 meters) in Subic Bay. With Nitrox 26, I only got 7 minutes of no-deco time ... the tech-divers on that dive got to spend a lot more time at-depth, at the admitted cost of carrying a bottle of deco-mix for planned decompression.

The option of 'planned decompression' is very seductive to me ... but let me return to my question:

What SAC rate is acceptable, for tech-diving training?

 

[muzikbiz22]

Rebreather

 

[BeijaFlor]

As in, travel with a rebreather? Carry my own rebreather?

 

[muzikbiz22]

As in, travel with a rebreather? Carry my own rebreather?

Lot's of people do. Just saying it's an option, and worthy of a look.

 

[BeijaFlor]

Maybe I'm over-reacting, but "rebreather diving" seems, to me, way more technical than "planned deco" diving, which is as far as I'd like to carry "tech diving."

May I be honest? "Rebreather diving," as it's practiced nowadays, involves way more than planned deco ... especially if we regard it as completely-closed-circuit rebreather diving. It would limit me to diving at places, at dive-shops, that had the brand and model of rebreather I'd learned to use in my training, and that's way more limiting than diving side-mount.

Beyond that ... I'm not diving in my close neighborhood. I'm flying to my dive-destinations -- tens of thousands of miles, e.g. from the East Coast of the USA to the Philippines, or maybe to other South-Pacific or South-Asian destinations. I CANNOT carry pressurized scuba-tanks, of oxygen-mix or diluent-mix, on those flights ... for reasons that I understand as an airplane pilot in my own right, since way before I got into scuba-diving.

What's left for me to do?

 

[BeijaFlor]

Are you serious, musikbiz22? "Lots of people do" fly with their own rebreathers?

I carry a Hollis Katana BCD, two Mares MR-12 Abyss regulators, a butt-pouch of emergency gear (compass, whistle, and a DSMB with an up-line reel), Force Fins and tropical boots, plus a reasonable save-a-trip kit of tools and parts for my gear. This comes close to the 23-kilo limit for checked luggage ... I'm sure that a rebreather kit would weigh more!

Or, on the other hand, I could rely on rental rebreathers, and search for dive-shops that had the gear I was familiar with from my training ... or train-up with the gear they had, at the destination. Seems awfully chancy to me.

 

[KevinNM]

People who travel and dive rebreathers almost always bring their rebreather. They may or may not bring tanks. They certainly won't if they are using GUE style off-board to large steel tanks, but might carry a pair of 3L tanks. They might have to pay extra for baggage. And now you also understand the reason why people might buy the carbon fiber rebreather tanks despite the issues with them.

And a generic answer I saw in this forum on the SAC rate, 0.6 cu ft/min in a dry suit and doubles while swimming at a relaxed rate.

 

[sigxbill]

a generic answer I saw in this forum on the SAC rate, 0.6 cu ft/min in a dry suit and doubles while swimming at a relaxed rate.

that's a good rate - except I'd have called that RMV ...

 

[Ankush Mittal]

Carrying your own rebreather is not that big a deal if you are serious technical diver. From what I understand once you start enjoying the benefits of rebreathers then there is no going back.

But, there are downsides. First being cost, the equipment itself is expensive let alone the training. If I understand correctly, there is generic rebreather training and then there are training specific to your rebreather. So if for some reason you decide to change your rebreather, you would need a set of training agasin to ensure you know how to operate your rebreather optimaly. The cost of the input are high as well along with accessories, gases etc.

Second being safety. Rebreathers while being safe enough if all precautions are taken into account, as we all know the chances for human errors just make the dangers of rebreathers extremely high. If the system isn't putting in enough oxygen into the mix you may not realize it until its too late by which time you would have been breathing CO2 and you will start convulsing. If this happens in the recreational depth you will most likely be fine, but if this happens deep then goodbye.

The chances you will catch on fast is high in the shallower depths but Murphy's Law. There are many reasons a rebreather may fail. Statistically speaking, the number of rebreather deaths are too high for me to even take a gander at this time. Given that the deaths are mostly Human error, I would not take that risk and stick to decompression diving.

I will be doing my TDI Advanced Nitrox + Deco Proceedures course in February so have been doing extensive research on this topic.

 

[Patoux01]

Second being safety. Rebreathers while being safe enough if all precautions are taken into account, as we all know the chances for human errors just make the dangers of rebreathers extremely high. If the system isn't putting in enough oxygen into the mix you may not realize it until its too late by which time you would have been breathing CO2 and you will start convulsing. If this happens in the recreational depth you will most likely be fine, but if this happens deep then goodbye.

I would recommend learning a bit more about how rebreathers work and how your body reacts to CO2, and that you do some more research, before explaining how it works to other people. No I will not go over it for you, they're simple systems and the way they work is largely explained all over the web. (Please don't get offended)


Rebreathers are routinely moved by planes. You just have to find a shop that can get you sorb, O2 and dil (preferably they have a set of tanks for you, but some divers take their own tanks with them...).


Finally, in terms of SAC, I don't think it really matters, I'd guess most tech divers are somewhere between 10 and 15 l/minute, occasionnally jumping higher to maybe 20...