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St.jimmy
01-20-2008, 14:06
Howdy!

Me and my dad (aka my dive buddy) were wanting to get a redundant air system. We can get a pony with regs and sheath (9cf, 3000psi) for 475 us, or a spare for 200 each. I've heard that spare airs aren't worth the cost, but I wanted to get a second opinion.

EDIT: okay I suck at typing.

SarahBella
01-20-2008, 14:32
Best thing to do is to figure out how many breaths you will need to get you back to the surface from your normal diving depth. The 3.0 cf spare air is one third of the 9cf pony. The pony set up is more cash up front but having an OOA emergency at 80 feet might make you feel like it was money well spent.

cgvmer
01-20-2008, 15:08
The answer to this depends on what kind of diving and where you do it.

If your diving shallow warm the 3 might be fine, diving NJ cold and dark ....go for a 30

marchand
01-20-2008, 15:25
try doing a search and I'm sure you will find all of the information you need.

Personally, I would not waist my money on a spair air because if you decide to get into more technical diving you can use that 9cf tank for your dry suit while a spair air will make you wish you never got it.

whse56
01-20-2008, 15:29
In previous posts on this subject I got the feeling that most of the people on this forum think of the spare air as next to worthless. 3 cubic feet of air will not last you very long so they seem to think you would be better off buying a 20, 30 or 40 cf pony setup. If you do wreck or cave diving or most of your dives are below 100ft or if you ride the edge of the no decomp charts you should go for a pony. If your diving is more of the rec type or if you travel by air to dive I would look at a spare air. I would rather have a spare air on my rig than nothing, I haven't seen to many pony setups on dive trips probably due to the hassle of packing and checking a tank and reg setup. Even at 100ft the 3cf spare air should get you about 10 breaths which would be enough to get you to the surface (without the 15ft decom stop) without having to rush it. You'll probably hear a lot of people that disagree with me. just my two cents

MSilvia
01-20-2008, 17:49
We can get a pony with regs and sheath (9cf, 3000psi) for 475 us, or a spare for 200 each. I've heard that spare airs aren't worth the cost, but I wanted to get a second opinion.
In my opinion, you should evaluate what your needs are, and base your decision on that. If you dive to "advanced open water" depths, it's entirely possible neither option will be sufficient. Personally, my "pony" is a 30 cubic foot tank. I wouldn't count on a 9 unless I was willing to ditch my buddy without telling him, ascend without returning to the mooring line, and then blow off my safety stops. I wouldn't count on a 3 to do anything other than help me extract myself from a crashed helicopter, overturned boat, or the like. I think a spare air, in most circumstances, is wholly inappropriate for a diver.

For a scenario that illustrates why, see my post in the redundant breathing systems thread here (http://forum.scubatoys.com/108380-post20.html).

Kidder
01-20-2008, 18:38
with the cost that was involved I recently got one of the big Ponys from scuba toys for Christmas. My buddy and I are thinking that once it is slung properly we will barely notice it.

DivingCRNA
01-20-2008, 18:44
Even at 100ft the 3cf spare air should get you about 10 breaths which would be enough to get you to the surface (without the 15ft decom stop) without having to rush it.

This depends entirely on your SAC, which is bound to increase with the stress of finding yourself out of air in a recreational dive. 10 breaths will not get a freaked out diver up from 100 feet witout risking AGE or DCI. Also-the 15 foot stop is a SAFTEY stop, not a decompression stop. A spare air is completely inappropriate for decompression diving.

MSilvia
01-20-2008, 19:24
Also-the 15 foot stop is a SAFTEY stop, not a decompression stop.
On the contrary, it is a decompression stop, but it's only done to add a margin of safety to a dive that would probably be okay without it. It adds that safety precisely because it gives dissolved gas in your tissues additional time to decompress before you surface.

cummings66
01-20-2008, 20:00
That goes towards all dives are deco dives, and probably I think has already been proven. If I recall right I think that since the stop was introduced DCI incidents have decreased.

BouzoukiJoe A.K.A. wrecker130 AKA Chuck Norris AKA joeforbroke (banned)
01-20-2008, 20:02
Also-the 15 foot stop is a SAFTEY stop, not a decompression stop.
On the contrary, it is a decompression stop, but it's only done to add a margin of safety to a dive that would probably be okay without it. It adds that safety precisely because it gives dissolved gas in your tissues additional time to decompress before you surface.

And skipping a 'mandatory safety stop' which the RDP requires after any dive exceeding 100 ft (and in other circumstances) is omitting a deco obligation. Of course its better to blow it off than drown but you are increasing your risk of DCS from perhaps negligible to something non-negligible. The stop is mandatory for a reason.

whse56
01-20-2008, 20:49
I'm not saying that a spare air is better than a pony set up, it obviously isn't. If the choice is not having a seperate backup air source (due to cost or flying to dive and can't/don't want to travel with a pony) or having a spare air, I'll take a spare air everytime. But I don't cave,wreck,tech dive, my diving so far is limited to 100ft maximum rec diving.

BouzoukiJoe A.K.A. wrecker130 AKA Chuck Norris AKA joeforbroke (banned)
01-20-2008, 21:56
Spare air is definitely better than no air. I have a 40cf pony. Hopefully I will never need it.

texdiveguy
01-20-2008, 22:21
That goes towards all dives are deco dives, and probably I think has already been proven. If I recall right I think that since the stop was introduced DCI incidents have decreased.

BINGO!!

Mtrewyn
01-20-2008, 23:11
Spare air is definitely better than no air. I have a 40cf pony. Hopefully I will never need it.

There is alot of info on this on this board, I think the common thought is some is better than none, but if your are going to go with a redundant system, I think you can get a 13 CF tank for not a lot of cash and it is small enough that you won't really notice it that much if at all. you still need the reg, and the gage but all said and done, a lot more safety for not that much more cost.

Just my 2 PSI :smiley2:

Grin
01-21-2008, 09:01
It appears you have to figure out your pony settup for you yourself. There are so many differnt pony settups for virtually every poster.
Personally, I think a 13 or 19 pony is the ticket for normal open water no deco diving to around 120 ft (what I do). I have a 13, and I rarly ever go deeper than 90 ft. If I have a issue I am going on the pony and starting my accent instantly. It seems differnt divers, different locations, different types of dives determine your redundant air source. I could not imagine using a 30 or 40 for my type of diving. And I also could not imagine slinging it either. But for others dive styles this is the preferred method. So it appears to me you just have to figure out what works for you.
Spare airs might work for someone, but I think most who use them have not really researched everything about how they should use one correct. Most buy them because they are the cheapest thing that gives them security. The big thing I fear could happen to many with the spare air is: They are going to be freaked out and trying to breath on that spare air, and also trying to swim up as fast as possible, knowing the spare air is not going to last. This opens the door to AGE bigtime. Not to mention the fact that DCS could follow, if you do avoid AGE.
Basically you either accend slow and correct, or you don't. A correctly sized pony is the only way to do that IMO. With Spare airs the primary thought is getting up top fast, same as it is without a spare air. With a pony the thought is doing a correct accent, as should be the priority. Huge difference!
Figure out what your proceedure is, if you go for that next breath and it is not there, and pick a pony settup to do what you need it to do.
Do you need to find your buddy? How deep are you? How slow of accent do you want to do? How much gas do you think you'll be sucking in a slight panicked mode? Do you need to be able to see the ponys pressure gauge to be comfortable while doing this semi emergency accent(back mounted or slung or a pressure gauge on a hose or?). Are you going to run the pony valve on all the time, or are you going to turn it on when you need it?

MSilvia
01-21-2008, 09:44
It appears you have to figure out your pony settup for you yourself. There are so many differnt pony settups for virtually every poster.
Akong those lines St.Jimmy, if you need help figuring out what really meets your needs, I'm sure we'd all be willing to help with that.

If you know your air consumption rate (and your dad/buddy's) let us know. If you don't know how to calculate it, let us know that too. Also let us know where you dive most often, your typical and maximum depths, and what the conditions are usually like. Once we have that info, we could all give you a bunch of different opinions and justifications about what we think you need.

Failing that, I'd recommend getting the higher capacity of the options you're considering.

Mycroft
01-21-2008, 21:43
Let's see if my calculations match yours.

My last three dives have an SCR of: 30.6, 36.5, and 32.3 - in the 36.5 dive, we had a hard swim between wrecks.

My "ceiling" is 100ft deep, by my medical profile, so I need enough gas to go from 100ft to the surface. I come up with needing a pony of approximately 27 cubic feet?

That assume the worst of those three SCR rates, and a three minute ascent. Actually, I would figure better then that by go for the worst case.

St.jimmy
01-22-2008, 17:24
Uhh, how do I do my SCR rate? My dad's I have no idea about, but for me...
Best example I have is a dive to ~65 fsw, approx 30 min, with 1000 psi one minute into the safety stop. Cold water, 7mil farmer john. Although, I willl have to redo my cert dives (see my thread in the accidents forum), and our instructor is giving us some pool time, so I can get the #s from there.

jeepbrew
01-24-2008, 10:28
While the Spare Air is better than no air, you are much better off with a Pony setup... I have a 19 and a 30 cf pony... usually carry the 30 when going real deep but hope to not need it.

texdiveguy
01-24-2008, 10:43
Uhh, how do I do my SCR rate?

SAC Calculator (http://www.spearfishing.org/bruces_tips/java/sac.html)

marchand
01-24-2008, 12:55
I got a sac of 0.4, is that good?

texdiveguy
01-24-2008, 13:00
I got a sac of 0.4, is that good?

That is very respectable for many diving situations :) ...keep up the good work....youth and staying in good physical condition will go along way to maintaining and improving SAC rates. I don't like talking about averages in divers as there are SO many variables...but a SAC of .5 - .6 is typical of sport divers....some folks its lower and others higher...it just all depends on dive profiles/diver physical conditioning/gear configuration/dive site condition/blablabla... and if its a 'full moon' out-lol.

St.jimmy
01-24-2008, 19:07
Guessing on the stats, based on what I know, my SAC was .6

MSilvia
01-25-2008, 09:53
Assuming 65 feet is typical of what you'd consider a deep dive, and using .6 for your SAC, here's a gas consumption estimate for a direct ascent at 30 feet per minute with a 3 minute safety stop at 15 feet.


As you know, every 33 feet of sea water is equal to 1 atmosphere of pressure. 65 feet of depth/33 feet= 1.97 ATM. Of course, we have to add 1 for the atmosphere itself, so the ATA (atmospheres absolute) at 65 feet is 2.97.
You use .6 cu ft of gas per minute at 1 ATA, so at 2.97 ATA you can expect to use (.6*2.97) 1.8 cu ft/min.
When you run out of gas, let's assume it takes you one minute to switch to your backup and inform your buddy or otherwise take care of important things you need to do. during that minute, you use 1.8 cubic feet. As you begin your ascent, we'll stay on the conservative side and use the deepest depth you're at for any given minute, so while you ascend to 35 feet, you use another 1.8 cubic feet, for a total of 3.2 (which would drain a spare air).
At 35 feet, the ATA is 2.1. Ascending 20 feet to your safety stop should only take you 2/3 of a minute, so you'll use (.6*2.1*.66) .9 cu ft during that part of your ascent, for a new total of 4.1 cubic feet.
In 3 minutes at 15 feet (1.46 ATA), you'll use another (.6*1.46*3) 2.7 cubic feet, for a total of 6.9 cubic feet. Surfacing from 15 feet should use another .5 or so if we keep with the conservative rule of always rounding up.
That makes the total you can expect to use while calmly and safely aborting a 65 foot dive in a direct ascent 7.4 cubic feet. That assumes you stay calm, and do a direct free ascent to the surface without returning to a mooring, anchor line, or other reference point. Naturally, if you get excited, work harder, or stay down for longer than a minute, you'll need a little extra.If my assumption about 65 feet is correct, I can't recommend you get a backup with less than a 7.5 cubic foot capacity. If you don't intend to push beyond those depths, a 9 cubic foot tank might be a good option, as you should be able to surface without sucking it dry. Of course, in my opinion, you get a lot more flexibility with a larger cylinder... if you someday decide you want that pony on a 100 foot dive, you want it to be able to get you home.

wheelman
01-25-2008, 12:51
Assuming 65 feet is typical of what you'd consider a deep dive, and using .6 for your SAC, here's a gas consumption estimate for a direct ascent at 30 feet per second with a 3 minute safety stop at 15 feet.

Not trying to be rude but I assume you were meaning 30 feet per minute not second.

Mtrewyn
01-25-2008, 23:36
I'm sure he was, 30 ft per minute.

MSilvia
01-28-2008, 13:51
Not trying to be rude but I assume you were meaning 30 feet per minute not second.
Yeah... good catch! At least I got it right in the calculations.

I edited the post to correct the error. Thanks again... and if you ever catch me advocating an 1800 ft/minute ascent rate, by all means be as rude as necessary. Better that than someone gets hurt taking my mistake at face value.

cummings66
01-28-2008, 17:42
I never noticed it, I read into it the correct values. People tend to do that while reading material, no matter how bad it's spelled you tend to correct it automatically.

At any rate, I hope everybody here that's posted figures has shown the spare air guys how useless it really it.

Mycroft needs to post more details, I'm assuming he's posted psi based figures and it varies according to tank and depth. Without both figures, especially depth it means nothing. 30 psi per minute at 100 feet is better than 30 psi per minute at the surface for example.

Gombessa
01-28-2008, 17:46
I haven't used either, but from what I remember the larger (more useful?) SAs are not so cheap. It just seems like you get more bang for the buck or experience with a pony, especially if you might be thinking about moving to stage bottles or deco later?

Mycroft
01-28-2008, 18:20
I never noticed it, I read into it the correct values. People tend to do that while reading material, no matter how bad it's spelled you tend to correct it automatically.

At any rate, I hope everybody here that's posted figures has shown the spare air guys how useless it really it.

Mycroft needs to post more details, I'm assuming he's posted psi based figures and it varies according to tank and depth. Without both figures, especially depth it means nothing. 30 psi per minute at 100 feet is better than 30 psi per minute at the surface for example.

What I posted was in PSI and it is SCR, not SAC. And here is the results of the program doing the calculation. Your SAC calculator shows .86, which considering my age and size isn't that bad.

Dive # = 129
Temperature of air = 27 C 81 F
Temperature of water = 25 C 77 F
Timestamp: = 2008 Jan 10 09:01:34 GMT
Dive recording interval = 20 Seconds
Length of dive = 00:27
Max depth this dive = 16.67 Meters 55 Feet
Location: St. Maarten, Net Place: Lucy's Barge
Tank size: 11.4 Liters 80.0 Cubic feet
Gas used: 136 Bar 1972 PSI
Dive type: No decompression, Single ascent, Salt water, SCR
Dive actions: Wreck-dive
Dive Computer type: Aladin Air Z O2
INT Meters Bar Feet PSI SCR O2%
1 - 8.1 | 1 ||| 27 | 7 ||| 0.0 ||| 21% |
2 - 14.5 | 1 ||| 48 | 7 ||| 9.8 ||| 21% |
3 - 16.4 | 1 ||| 54 | 7 ||| 8.2 ||| 21% |
4 - 15.9 | 1 ||| 52 | 7 ||| 8.1 ||| 21% |
5 - 16.6 | 1 ||| 54 | 7 ||| 8.1 ||| 21% |
6 - 16.6 | 1 ||| 54 | 7 ||| 8.0 ||| 21% |
7 - 16.1 | 1 ||| 53 | 7 ||| 8.0 ||| 21% |
8 - 15.8 | 1 ||| 52 | 7 ||| 8.1 ||| 21% |
9 - 15.5 | 1 ||| 51 | 7 ||| 8.2 ||| 21% |
10 - 16.1 | 1 ||| 53 | 7 ||| 8.2 ||| 21% |
11 - 16.3 | 1 ||| 53 | 7 ||| 8.1 ||| 21% |
12 - 15.9 | 1 ||| 52 | 7 ||| 8.1 ||| 21% |
13 - 16.1 | 1 ||| 53 | 15 ||| 17.4 ||| 21% |
14 - 15.8 | 1 ||| 52 | 15 ||| 17.4 ||| 21% |
15 - 14.8 | 1 ||| 49 | 15 ||| 17.8 ||| 21% |
16 - 14.2 | 2 ||| 47 | 22 ||| 26.9 ||| 21% |
17 - 14.6 | 2 ||| 48 | 22 ||| 27.1 ||| 21% |
18 - 13.6 | 2 ||| 45 | 22 ||| 27.4 ||| 21% |
19 - 13.3 | 2 ||| 44 | 22 ||| 28.1 ||| 21% |
20 - 11.9 | 2 ||| 39 | 22 ||| 29.2 ||| 21% |
21 - 13.0 | 2 ||| 43 | 22 ||| 29.4 ||| 21% |
22 - 13.5 | 2 ||| 44 | 22 ||| 28.5 ||| 21% |
23 - 13.5 | 2 ||| 44 | 22 ||| 28.3 ||| 21% |
24 - 13.5 | 2 ||| 44 | 22 ||| 28.3 ||| 21% |
25 - 13.2 | 2 ||| 43 | 30 ||| 38.8 ||| 21% |
26 - 12.7 | 2 ||| 42 | 30 ||| 39.3 ||| 21% |
27 - 12.7 | 2 ||| 42 | 30 ||| 39.6 ||| 21% |
28 - 12.4 | 3 ||| 41 | 37 ||| 49.2 ||| 21% |
29 - 12.5 | 3 ||| 41 | 37 ||| 49.5 ||| 21% |
30 - 12.5 | 3 ||| 41 | 37 ||| 49.5 ||| 21% |
31 - 11.9 | 3 ||| 39 | 37 ||| 50.2 ||| 21% |
32 - 11.8 | 3 ||| 39 | 37 ||| 50.9 ||| 21% |
33 - 12.7 | 3 ||| 42 | 37 ||| 49.8 ||| 21% |
34 - 13.5 | 2 ||| 44 | 30 ||| 39.1 ||| 21% |
35 - 13.6 | 2 ||| 45 | 30 ||| 38.3 ||| 21% |
36 - 12.7 | 2 ||| 42 | 30 ||| 38.8 ||| 21% |
37 - 11.0 | 2 ||| 36 | 22 ||| 30.2 ||| 21% |
38 - 10.8 | 2 ||| 35 | 22 ||| 31.8 ||| 21% |
39 - 10.5 | 2 ||| 34 | 22 ||| 32.3 ||| 21% |
40 - 11.1 | 1 ||| 36 | 15 ||| 21.8 ||| 21% |
41 - 11.1 | 1 ||| 36 | 15 ||| 21.5 ||| 21% |
42 - 9.5 | 1 ||| 31 | 15 ||| 22.3 ||| 21% |
43 - 11.7 | 2 ||| 38 | 22 ||| 32.3 ||| 21% |
44 - 12.4 | 2 ||| 41 | 22 ||| 30.0 ||| 21% |
45 - 13.2 | 2 ||| 43 | 22 ||| 29.0 ||| 21% |
46 - 12.9 | 2 ||| 42 | 30 ||| 39.3 ||| 21% |
47 - 12.1 | 2 ||| 40 | 30 ||| 40.1 ||| 21% |
48 - 12.4 | 2 ||| 41 | 30 ||| 40.4 ||| 21% |
49 - 12.7 | 2 ||| 42 | 22 ||| 29.2 ||| 21% |
50 - 11.3 | 2 ||| 37 | 22 ||| 30.0 ||| 21% |
51 - 9.4 | 2 ||| 31 | 22 ||| 32.5 ||| 21% |
52 - 10.9 | 1 ||| 36 | 15 ||| 22.3 ||| 21% |
53 - 12.5 | 1 ||| 41 | 15 ||| 20.8 ||| 21% |
54 - 12.7 | 1 ||| 42 | 15 ||| 19.9 ||| 21% |
55 - 13.0 | 2 ||| 43 | 30 ||| 39.3 ||| 21% |
56 - 13.0 | 2 ||| 43 | 30 ||| 39.1 ||| 21% |
57 - 12.7 | 2 ||| 42 | 30 ||| 39.3 ||| 21% |
58 - 13.2 | 3 ||| 43 | 37 ||| 48.5 ||| 21% |
59 - 13.5 | 3 ||| 44 | 37 ||| 47.9 ||| 21% |
60 - 12.9 | 3 ||| 42 | 37 ||| 48.2 ||| 21% |
61 - 11.8 | 2 ||| 39 | 30 ||| 40.4 ||| 21% |
62 - 11.4 | 2 ||| 37 | 30 ||| 41.8 ||| 21% |
63 - 11.9 | 2 ||| 39 | 30 ||| 41.8 ||| 21% |
64 - 13.0 | 3 ||| 43 | 37 ||| 49.5 ||| 21% |
65 - 13.9 | 3 ||| 46 | 37 ||| 47.3 ||| 21% |
66 - 15.2 | 3 ||| 50 | 37 ||| 45.2 ||| 21% |
67 - 15.2 | 3 ||| 50 | 37 ||| 44.1 ||| 21% |
68 - 14.6 | 3 ||| 48 | 37 ||| 44.7 ||| 21% |
69 - 13.9 | 3 ||| 46 | 37 ||| 45.8 ||| 21% |
70 - 12.4 | 2 ||| 41 | 30 ||| 38.8 ||| 21% |
71 - 12.9 | 2 ||| 42 | 30 ||| 39.9 ||| 21% |
72 - 14.3 | 2 ||| 47 | 30 ||| 38.3 ||| 21% |
73 - 12.7 | 2 ||| 42 | 22 ||| 28.1 ||| 21% |
74 - 7.4 | 2 ||| 24 | 22 ||| 33.0 ||| 21% |
75 - 5.2 | 2 ||| 17 | 22 ||| 40.7 ||| 21% |
76 - 5.4 | 2 ||| 18 | 22 ||| 43.1 ||| 21% |
77 - 5.5 | 2 ||| 18 | 22 ||| 42.7 ||| 21% |
78 - 5.4 | 2 ||| 18 | 22 ||| 42.7 ||| 21% |
79 - 5.4 | 2 ||| 18 | 30 ||| 58.2 ||| 21% |
80 - 5.2 | 2 ||| 17 | 30 ||| 58.8 ||| 21% |
81 - 5.4 | 2 ||| 18 | 30 ||| 58.8 ||| 21% |
82 - 5.0 | 1 ||| 16 | 7 ||| 13.9 ||| 21% |
83 - 0.5 | 1 ||| 2 | 7 ||| 16.5 ||| 21% |
84 - 0.8 | 1 ||| 3 | 7 ||| 19.5 ||| 21% |
85 - 0.5 | 0 ||| 2 | 14 ||| 39.0 ||| 21% |
86 - 0.5 | 0 ||| 2 | 14 ||| 39.6 ||| 21% |
87 - 0.0 | 0 ||| 0 | 14 ||| 40.8 ||| 21% |
88 - 0.0 | 0 ||| 0 | 14 ||| 42.0 ||| 0% |
89 - 0.0 | 0 ||| 0 | 14 ||| 42.0 ||| 0% |
90 - 0.0 | 0 ||| 0 | 14 ||| 42.0 ||| 0% |
Avg SCR | 32.3 | Depth | 37.1 FT | PSI Used | 2037 | Timespan: 29.7