Redundant Air questions

[dkiely]

I want to get a redundant air set up. I think the SpareAir is to small, but I'm open to it if anyone has had good experiences with them. I'm looking at either a 19 cu. ft. bottle or a 6 cu. ft. bottle. I'm not sure what size, I'm open to suggestions and pros/cons of each size. For regulators I've been looking at the Zeagle Razor set up, or a standard tank valve and using one of the regulators I no longer use as an octo.

Looking to see what everyone likes and pros/cons to both tank sizes as well as both regulator setups.

Thanks for the help!

 

[spectrum]

Here is an old post that provides an objective sizing calculation.

With regard to set-up a sling is easier, less expensive and more versatile. Many divers will have enough spare parts and scrap to build a nice sling. A sling is quick and easy to take and is not rig specific. A sling makes it easy to hand off to a needy buddy.

Any regulator up to the dive will do. The biggest question is often what to use for a gauge.

The other hot button is retention of your alternate second stage for your back gas. Solo divers are likely to remove it but in any case it removes an access point.

Pete

 

[decompression]

Take good look at the dive profiles you'll be doing. Calculate how much air it will take to get you safely back to the surface, at the end of the dive, deepest point. Quite often the spare airs just don't cut it. Often an AL 30 or 40 slung is a very good alternative.

My preference is sidemount, true redundancy and a wide variety of tank choices.


Sent from my iPhone using Tapatalk

 

[Kairoos]

I sling an AL30 and under the water it's like nothing. It is a bit cumbersome on a cramped dive boat though! Just a standard AL30 with an inexpensive reg set and a button SPG.

I did pick up this kit:
Highland by XS Scuba Stage Bottle Strap Kits

Although you can probably put it all together cheaper, it wasn't worth my time to save a couple dollars.

 

[Kevrumbo]

From 18m/60' deep:
Tally the ATA's. . .
2.8
2.5
2.2
1.9
1.6
1.3
----
Total: 12.3

Multiply 12.3 ATA by 30 liters/min*ATA stressed RMV equals 370 liters needed to get you (and only you!) to the surface at an easy conservative slow controlled ascent rate of 3m/min: a full fill AL13 pony with 377 liters will do. For the max recommended ascent rate of 9m/min, a full fill AL6 with 170 liters would suffice.

From 30m/100' deep:
4.0
3.7
3.4
3.1
2.8
2.5
2.2
1.9
1.6
1.3
----
Total: 26.5

Multiply 26.5 ATA by 30 liters/min*ATA stressed RMV equals 800 liters needed at an easy conservative slow controlled ascent rate of 3m/min, a full fill AL30 pony with 850 liters will work; for the faster ascent rate of 9m/min, an AL13 with minimum 270 liters will do.

AL6 (0.8L/bar metric tank rating);
AL13 (1.9L/bar); AL30 (4.2L/bar).

 

[DevonDiver]

Here's my article on that subject..
Scuba Diving with a Pony Cylinder

 

[Steve_C]

Wanted it lighter and smaller on the boat. Wanted enough air to get me or buddy back up. Went with a slung AL19. Small enough that I actually will take it diving most of the time locally in salt water.

 

[uncfnp]

David. This is a frequent and much debated topic on SB. Lots of threads.

If you look around many of the dive boats in the WPB area you will see a variety of ponies in use. I have seen spare air's, 13's, 19's, 30's and once a 40... But the diver left it on the boat. The one I see male divers using most often is the 19 cf. It has plenty of gas to get even an air hog safely to the surface from recreational depth, can sling or tank mount, takes up very little additional space on the dive boat and is less like to be left behind (especially on the shallow dives when you might decide its not worth the hassle).

True, once underwater there is little difference in the sizes, top side the difference can be meaningful.

An arguement you will often see is that a 30 or 40 will take you into tech. For this it really needs to be a 40. If you do decide to go with the larger tank just be sure you will be willing to deal with the size on the boat and not decide to just leave it home. I prefer to have the right tank for the job rather then buying for what might be needed for other uses and on recreational dives found in the WPB/Jupiter area its a 13 or 19 for the majority of divers.

 

[DA Aquamaster]

To me, an AL 19 has never made any sense, when an AL 30 does everything better for a marginal increase in size and weight.

The difference between an AL 19 and an AL 30 is a half inch in diameter and 3" in length, and none of that is noticeable in the water, regardless of how you carry it. The AL 30 is about 3 pounds heavier overall out of the water (11 pounds versus 8 pounds) but it is .4 pounds less negative in the water (-1.0) when full.

The AL 30 also has the advantage of holding 30 cu ft at 3000 psi, so a button gauge allows you to easily assess remaining gas - 2,000 p= 20 cu ft, 1500 psi = 15 cu ft, etc - even if you are seriously math challenged.

And with 30 cu ft it has enough capacity to provide a more than adequate reserve for pony use, even if it isn't completely full.

Strangely enough I've been involved in technical diving for over 20 years now, and we primarily cave dive, usually encountering deco on almost every dive, unless it's very shallow cave - and I've never seen the need to own a AL 40.

Thus I'm surprised to hear "you really need a 40" if you move into tech. Well...surprised isn't the word as you hear that a lot, but it's perhaps a little disconcerting that so many technical divers fail to think it through and just accept it at face value.

Looking at it objectively, an AL 30 is large enough to be a useful deco bottle with enough O2 capacity to provide for a fair amount of deco at 20' plus a1.5x reserve.

Even with a fairly high SAC rate of .6 cfm on deco, it will allow for a full 20 minutes of deco at 20' with a 50% reserve, or if you complete the last stop at 10' about 6 minutes at 20' and 18 minutes at 10 ft.

With a better deco SAC of .4 cfm, the numbers rise to 31 minutes at 20 ft with a 50% reserve, or 9 minutes at 20ft and 25 minutes at 10 ft with a 50% reserve.

If you're getting into more deco than that, you should be doing a two deco gas dive, in which case you'll quite often use the first deco gas as a travel gas if it's a trimix dive, so you'll be using an AL 72 or an AL 80 for that gas and you still won't need a 40.

And if you're doing an offshore trip with limited access to O2 fills you'll want an AL 72 or AL 80 for your O2 bottle anyway, so once again an AL 40 isn't really needed.

Now, an AL 40 makes perfect sense for a technical diver who doesn't have an AL 30 when he or she starts technical diving and the extra 10 cu ft certainly doesn't hurt. However with the AL 40 being once again a half inch larger in diameter, 3" longer and 4 pounds heavier than an AL 30 - a total of 5.25" in diameter, 24.75" in length and 15 pounds in weight, AN AL 40 is arguably too large and heavy for a pony bottle, so it's hard to advocate for an AL 40 for a recreational diver. And the AL 40 feels larger in the water than an AL 30.

So don't discount the AL 30 for technical diving as it fits quite well into both single and two gas deco dive plans.

 

[uncfnp]

...//...

Thus I'm surprised to hear "you really need a 40" if you move into tech. Well...surprised isn't the word as you hear that a lot, but it's perhaps a little disconcerting that so many technical divers fail to think it through and just accept it at face value...//...

You are right, I phrased that badly. I should have said that in my limited experience, instructors prefer the 40. My O2 bottle is actually a 30 but I was discouraged from this. I think it was on the possibility of using the tank for 50 and 80 mixes as well.

Now, putting that same philosophy to the pony...