Redundant Air questions

[scubadada]

A 19 is more than adequate for me and I find it much easier to pack. If there was a 13 that was similar in length but smaller diameter I would go to that. But the typical 13 is a fat little thing and simply does not sling well. Therefore I find the 19 perfect for my uses. N

+1, a 19 gives me a minute at depth, normal ascent, normal safety stop, at twice my normal SRMV. Of course, Nemrod is one of the few with a lower SMRV than mine

I agree with Dumpster, a 6 would not easily get me straight to the surface from 130 without hurrying a bit . I don't think some people make the calculations. Of course, getting to the surface is a good thing, you could have a double Spare Air

 

[Kevrumbo]

Just my 2 cents. First, if you don't lose your head 6cf will get you up from 130 feet. Let's do the math. 130 to 70 - one minute at 60 feet/minute. 70 to 40 - another minute at 30 feet/minute. 40 to safety stop depth, another minute. If you are sucking down air - even at 2 cf/min - you will be fine. Sans panic, at a SAC of 1.0 (conservative) you will still have time for a short safety stop.

I (very recently) downsized from a 13cf to a 6cf for just that reason. It's a last resort, get me up safely resort. Too many over complicate the issue. Too many think you need more air than just to surface. Nonsense. If your equipment is well cared for a pony is very good insurance. However, you don't need to carry vastly more than you need.

As an aside, if you want a 13 cf pony i have one that just had hydro & vis and set up with sling. PM me if interested.

Are you assuming a SAC of 1 cu-ft/min in the above referenced ascent scenario? If so, I'm not so sure your numbers work for an ascent from 130 ft using a 6-cu-ft pony bottle? Can you clarify your assumptions/calculations?

. . .I agree with Dumpster, a 6 would not easily get me straight to the surface from 130 without hurrying a bit . I don't think some people make the calculations. Of course, getting to the surface is a good thing, you could have a double Spare Air

Let's just do an easy quick estimate from 130' to 70':
Tally the ATA's:
4.9
4.6
4.3
4.0
3.7
3.4
3.1
----
Total: 28

Multiply 28 ATA by 1 cuft/min*ATA stressed SAC/RMV equals 28 cuft consumed at a slow conservative ascent rate of 10'/min; for an emergency max ascent rate of 60'/min then, estimate 5 cubic feet consumed.

Therefore an AL6 pony bottle should last from 130' to 70' with a stressed SAC rate of 1 cuft/min. (And then for argument's sake, now figure in a panicked SAC rate of "2cuft/min" instead???) It's all academic --you're obviously gonna exhaust that AL6 before making it to the surface. . .

 

[DA Aquamaster]

A 19 is more than adequate for me and I find it much easier to pack. If there was a 13 that was similar in length but smaller diameter I would go to that. But the typical 13 is a fat little thing and simply does not sling well. Therefore I find the 19 perfect for my uses. N

Below is a 2L Faber FX 15 next to an AL 13. The FX 15 holds 15 cu ft at 3442 psi. It's the only slightly longer than an AL 13, but it's only 3.9" in diameter - an inch smaller than an AL 13.

Faber makes the 3L FX 23 as well. It has the same 3.9" diameter but it's 19.5" long - 1 inch taller than an AL 19.

Both the Fabers are 2.5 pounds negative when full, about a pound more negative than an AL 13 or AL 19.

 

[decompression]

Hp air not always available.....but good side by side size comparison.


Sent from my iPhone using Tapatalk

 

[Nemrod]

Below is a 2L Faber FX 15 next to an AL 13. The FX 15 holds 15 cu ft at 3442 psi. It's the only slightly longer than an AL 13, but it's only 3.9" in diameter - an inch smaller than an AL 13.

Faber makes the 3L FX 23 as well. It has the same 3.9" diameter but it's 19.5" long - 1 inch taller than an AL 19.

Both the Fabers are 2.5 pounds negative when full, about a pound more negative than an AL 13 or AL 19.

Those are definitely interesting but for now I will stay with the 19. I am kind of shy with dealing with the 3400 psi fills and the additional negative buoyancy. And it is true, packing for air travel aside, a 30 does sling nicely also.

N

 

[Kharon]

It's all academic --you're obviously gonna exhaust that AL6 before making it to the surface. . .

I removed my reply and am disconnecting from the discussion. I know what works for me from actual experience and testing my limits. That may very well not work for others. Keep in mind academic calculations prove bumble bees can't fly.

 

[dumpsterDiver]

I removed my reply and am disconnecting from the discussion. I know what works for me from actual experience and testing my limits. That may very well not work for others. Keep in mind academic calculations prove bumble bees can't fly.

We don't need for you to admit that you are full of crap or delete your calculations (a simple admission that your math was very wrong would have been sufficient).

However, I find it really strange that you decide to continue to tell us you can make it from 130 to the surface with 6 cu-ft, but can't provide the math to demonstrate it!!!!

It is a lot easier to throw up some numbers (aggressive assumptions) that work - compared to actually performing the ascent -- sipping your air deep, from a tiny bottle - in a true emergency.

The fact of the matter is that it is possible to make an ascent from 130 on 6 cu-ft bottle, but you are going to need to make an accelerated ascent rate for the initial portions of the ascent, you are going to have ZERO time to play around on the bottom and you are going to need to keep your air consumption rate reduced, for at least the deeper portion of the ascent AND your safety stop is probably going to be shortened or eliminated.

People need to do the math themselves, actively develop the assumptions that THEY are comfortable with and then determine which bottle will meet their assumptions (which will hopefully be consistent with their NEEDS in an actual emergency).

Don't believe everything you read on Scubaboard.

 

[scubadada]

I removed my reply and am disconnecting from the discussion. I know what works for me from actual experience and testing my limits. That may very well not work for others. Keep in mind academic calculations prove bumble bees can't fly.

We don't need for you to admit that you are full of crap or delete your calculations (a simple admission that your math was very wrong would have been sufficient).

However, I find it really strange that you decide to continue to tell us you can make it from 130 to the surface with 6 cu-ft, but can't provide the math to demonstrate it!!!!

It is a lot easier to throw up some numbers (aggressive assumptions) that work - compared to actually performing the ascent -- sipping your air deep, from a tiny bottle - in a true emergency.

The fact of the matter is that it is possible to make an ascent from 130 on 6 cu-ft bottle, but you are going to need to make an accelerated ascent rate for the initial portions of the ascent, you are going to have ZERO time to play around on the bottom and you are going to need to keep your air consumption rate reduced, for at least the deeper portion of the ascent AND your safety stop is probably going to be shortened or eliminated.

People need to do the math themselves, actively develop the assumptions that THEY are comfortable with and then determine which bottle will meet their assumptions (which will hopefully be consistent with their NEEDS in an actual emergency).

Don't believe everything you read on Scubaboard.

Exactly. I could make it to the surface with a 6 cf with my average SRMV but that is not a good assumption to make. I make my calculations using twice my normal SRMV plus a little. I can make a nice leisurely ascent from 130 feet with a safely stop with about 15 cf. I can't quite make it to the surface with an aggressive, but safe, ascent on 6 cf. Do you want to have a small cushion for safety or push it to the limit to make it to the surface? No question for me, to each their own.

 

[dkiely]

It depends on a large degree on what type of diving you are doing, what you want the back up for, who you are diving with, what your comfort level is and what your philosophy is towards diving and personal safety/responsibility. I have read all the posts here and in the past and understand all the arguments. I can't really suggest what might be right for you based upon what little you provided but I can tell you what I do and what my thoughts are. For my shallow solo shore diving (30' or less) no overhead, I stopped carrying my small 6 cft back up. On warm clear boat dives with a buddy with no overhead environment I don't bother as well. On my warm clear solo shore dives to depths greater than 30' with no overhead environment, I carry on my side attached to my BCD a 6 cft bottle. I am comfortable in this environment going down to 100' or so with this rig. I know people like bigger bottles.

My thinking is that I will likely never use it. I would be an extremely rare situation that I will ever need it. If I ever do it will be simply to assist getting to the surface. I don't dive anywhere near deco on my deeper solos and would not plan on a safety stop on an emergency assent. This would be for a true emergency situation where on the next breath from my main there was no air type situation. I am confident with my training and experience that I could safely make it to the surface from depth with little extra air needed. Remember the standard assent rate was modified with the safety stop recommended added. I started diving way back when when the assent rate was faster with no recommended safety stops.

As I side note, over my 40 years of diving I note the trend for divers to "overgear up" in my humble opinion where divers can barely stand up, get up, off or on a boat without assistance from others in part because of all "extra" gear they carrying. I am heading in the other direction on this trend.

Hope this helps and as noted my comfort using a 6 is only in the environments I described. If you are in dark cold deep dives, deco or close, wreck penetrations, overhead issues etc I would not use only a 6 nor recommend a bottle that small.

I highly doubt I'll ever use it, but I'd rather be safe than sorry. My biggest reason for wanting to carry one is for other divers. I like the idea of being able to pass off a completely independent air source to a diver with an out of air situation or equipment failure.

---------- Post added December 20th, 2015 at 04:39 PM ----------

Below is a 2L Faber FX 15 next to an AL 13. The FX 15 holds 15 cu ft at 3442 psi. It's the only slightly longer than an AL 13, but it's only 3.9" in diameter - an inch smaller than an AL 13.

Faber makes the 3L FX 23 as well. It has the same 3.9" diameter but it's 19.5" long - 1 inch taller than an AL 19.

Both the Fabers are 2.5 pounds negative when full, about a pound more negative than an AL 13 or AL 19.

Where did you get the Faber tank? Doesn't look like I can purchase anything from their website

 

[Hatul]

We do a lot of shore diving so don't want to carry excess weight and bulk. My rule of thumb for rec, non-deco solo diving is 13 cf for depths <60 ft, and 19 for > 60 ft. If you do the calculations for moderate conservatism it allows a safe ascent in most OOA cases.