Foxfish
Contributor
How low would you draw down your main 12L air cylinder at 232 b diving solo with a 2.7L pony bottle at 200 b diving in the ocean. Without the spare air you'd normally surface with 50 b.
How low with spare air
- Thread starter Foxfish
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mala
Contributor
the stock answer is to ignore the gas in the pony and surface with 50bar.
as a solo diver you have to decide yourself depending on the dive.
better to ditch the pony for a bigger stage and not have the worry.
as a solo diver you have to decide yourself depending on the dive.
better to ditch the pony for a bigger stage and not have the worry.
Any gas you take for emergency use is exactly that - for emergency use. You still surface with the normal amount of air you would when planning a dive. And 50 bar isn't a sufficient answer. You need to consider depth when planning your dive. The deeper the dive the more you need to keep in reserve in your cylinder.
The OP may find this article enlightening... USING ADDITIONAL REDUNDANCY: the maligned and misunderstood pony bottle | Doppler's Tech Diving Blog
scubastingray
Contributor
If you plan to drain your main tank, what happens if your spare air fails?
Bob DBF
Contributor
50 b
The Spare Air is for an emergency, and not a very big emergency at that.
Bob
-----------------------------
... you've got to ask yourself one question: Do I feel lucky? Well, do ya, punk?
Harry Calahan
The most important thing to plan when solo diving is to make sure that you are not diving with an idiot. Dsix36
paulw
Contributor
You " draw down your main 12L air cylinder" to what ever you intend to end the dive with ignoring the pony tank. I would really suggest taking the Solo course or at the very least reading the book.
R
redacted
Guest
I do adjust my gas plan a bit when diving with a pony tank AND a buddy. In that case, I plan my gas as if I were diving solo.
One of the reasons for recommending that divers surface with 50 bar is that pressure gauges are not terribly accurate in the lower portion of their range. That fact doesn't change because you have hung a small bottle off your BC. If you are breathing your tank much below 50 bar, you are running an increasing risk of having to USE that little safety bottle. And there are tons of threads here about how little gas that is if you really need it, from any depth to speak of at all.
The bottom line is that if a gas supply is considered in your dive planning, it is not an emergency gas supply. It MAY represent a source of redundancy, but that depends on HOW the gas planning is done in the first place.
The bottom line is that if a gas supply is considered in your dive planning, it is not an emergency gas supply. It MAY represent a source of redundancy, but that depends on HOW the gas planning is done in the first place.
victorzamora
Contributor
Now that the main points have been covered (take the class, do NOT plan to use it on your dives, etc) I'd like to bring up two conflicting points.
1) I'd rather have a small tank with me on every dive than a larger tank that I leave behind on most dives. If it's small and convenient, I'm more likely to carry it. If it's bigger and less convenient, I'll be less likely to carry it.
2) Have you figured out how long it'll actually keep you alive? I did some quick math. The big unit (3cuft) has 2.5ft3 of "usable" gas (giving 500psi reserve, about 35bar). Assuming a SAC rate of 0.65 (pretty common amongst rec divers), and a dive to 100ft, and ascending immediately upon switching, you get 90 seconds of air. This is only if you don't have to purge the mouthpiece with compressed air, take a big gulp of air to recouperate, and then have an elevated breathing rate upon ascent. Also, this does not include spending time at depth doing anything. Including all of that, you conservatively get no more than 45 seconds of ascent. An ascent from 100ft in 45 seconds is extremely unhealthy, and is 2.88x the "recommended" ascent rate. If you take into account common "elevated" breathing rates, your numbers plummet to 25 seconds of ascent.
So, to answer my first point....your buddy should either be well ready to donate to you, and planning for "turn pressures" should be made, or your pony had better be bigger than a Spare Air. With a little tweaking and persistance, you should be able to sling an AL40 very comfortably on every dive. I know that's not necessarily relevant to your question....but it's something to think about.
1) I'd rather have a small tank with me on every dive than a larger tank that I leave behind on most dives. If it's small and convenient, I'm more likely to carry it. If it's bigger and less convenient, I'll be less likely to carry it.
2) Have you figured out how long it'll actually keep you alive? I did some quick math. The big unit (3cuft) has 2.5ft3 of "usable" gas (giving 500psi reserve, about 35bar). Assuming a SAC rate of 0.65 (pretty common amongst rec divers), and a dive to 100ft, and ascending immediately upon switching, you get 90 seconds of air. This is only if you don't have to purge the mouthpiece with compressed air, take a big gulp of air to recouperate, and then have an elevated breathing rate upon ascent. Also, this does not include spending time at depth doing anything. Including all of that, you conservatively get no more than 45 seconds of ascent. An ascent from 100ft in 45 seconds is extremely unhealthy, and is 2.88x the "recommended" ascent rate. If you take into account common "elevated" breathing rates, your numbers plummet to 25 seconds of ascent.
So, to answer my first point....your buddy should either be well ready to donate to you, and planning for "turn pressures" should be made, or your pony had better be bigger than a Spare Air. With a little tweaking and persistance, you should be able to sling an AL40 very comfortably on every dive. I know that's not necessarily relevant to your question....but it's something to think about.
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