spare air

[Graeme Tolton]

A big part of the reason that spare air's are bashed is that the marketing seems to be aimed at newer divers who are not well aware of the limitations of such a system. I have personally witnessed a diver carrying a spare air as his only means of redundancy on a 145' 40 degree F, fresh water dive. His only back gas, being an AL80 with a k-valve. Most other single tank k-valve divers doing this dive would be carrying at least an al30 as redundancy. If he were to have an ooa emergency and his buddy weren't close by, that wreck would have claimed another life. 3cf is not enough air from that depth.

 

[idocsteve]

I carried a Spare Air for years, then upgraded to a 19 cf pony.

Any extra air is better than no extra air as long as you don't change your dive plan because you know you've got the extra safety margin...but if you're going to do it, why not go with the pony...the cost is not all that much different.

I take the pony with me on air travel vacations too. You gotta watch the weight but it can work out if you only use one pair of underwear for the week.

 

[Crush]

I have a 19 cu ft pony that I sling. How big a tank do you need? That depends on how deep you want to go. I estimate a rock bottom of 130 feet for a 19 cu ft pony - here is why:

If you have a surface air consumption of 1.0 (i.e., in cu ft / min) and run into trouble at 130 ft, with a 19 cu ft pony you have time to: (1) spend 1 min at 130 ft sorting out the problem; (2) ascend at at 60 ft/min from 130 to 30 ft; (3) above 30 ft ascend at 30 ft/min, including a 3 min safety stop at 20 ft.

The normal ascent profile (above) means that you can dive again that same day. A spare-air ascent may get you to the surface alive (which is all that really counts) since you stick it in your mouth and head up fast, but you shouldn't be diving for at least a few days. In my mind the pony outcome is better, but it does weigh more outside the water (in the water it is essentially weightless).

 

[Graeme Tolton]

When i was diving single tank, I would sling an al30. Diving doubles now, if i have anything extra, it is al al80, typically for longer bottom times. On any deeper dive, i follow the rule of thirds.

 

[W0X0F]

While the pro and cons of carrying a pony as a backup can be controversial, learning how to compute your SAC rate, then using it to estimate what air would be needed to safely ascend from a particular scenario is great training. I went through the exercise and now carry a 19cf pony on my dives. But, more importantly, I can explain why, and I know what it can and can't do for me, if necessary.

For me, the exercise in air consumption was also very informative in analyzing what a good "bingo" psi is going to be for a particular dive depth. This is particularly interesting when using different size tanks.

-Mike

 

[Hatul]

For recreational diving 19 cu ft is ideal. I have a 13 and it's too small.

Adam

 

[formula1mb@aol.com]

one thing to keep in mind too with a pony is to maintain it as religiously as your main regulator. so you can't just throw it in the corner after diving, esp in saltwater.

Regarding size, personally after calculating with a conservative SAC, I'm comfortable with a 13 cu ft for rec dives up to 50-60 ft, beyond that a 20 or more.

final note too from experience, make sure you maintain the air pressure in the pony----after using it for a couple of dives, it's easy for the pressure to drop a couple hundred psi from practice, turning it on and off, etc so even that 20 cu ft can easily become a 10 cu ft pony if you never top it off. good news though at least here in southern california, most shops like sports chalet will fill up a pony for free. personally I also have a transfill whip I picked up used---that way whenever I get my hp steel filled, I can top off my pony and even get it slightly higher to around 3200-3300 psi for that extra bit of air and so it lasts longer between fills.

 

[GrumpyOldGuy]

Advice on pony bottles varies widely since divers and dive conditions also vary widely.

My suggestion is to actually note the amount of air you use from a minute before the start of a of safe ascent to surface on a deep dive. You can then calculate the exact volume YOU needed based on tank size, double for possible stress and you have the correct minimum size for a pony for yourself. Not as fun as arguing on SB about sizes, but more accurate for you.

 

[DCBC]

To put things in perspective, I regularly teach an OW class to do a 50' CESA (emergency ascent) and my Advanced classes do 100' on one breath of air. If I had a Spare Air, I would feel very comfortable to do a 250' free ascent on a decompression dive to my staged cylinders. Unless I was diving in an overhead environment, there is NO reason why I would need a pony bottle to do a safe ascent (but I have carried a pony many years ago during wreck penetrations).

A number of divers today dive much deeper than they can do an emergency ascent on one breath of air. It doesn't matter if you need two or three breaths to attain the surface by CESA; either a Spare Air or a Pony will give you enough gas. If you want the luxury of breathing all the way and dive relatively deep, a pony is a good choice for you. One has the luxury of more air with a pony, the Spare Air offers less bulk. It comes down to the type of diving you do and what you feel most comfortable with.

When you find yourself in need of air and don't have any, either choice would be a welcome one. Is there anyone diving without a redundant air source that wouldn't welcome a few more breaths of air to get to the surface? Diving in an overhead environment is of course another story.

 

[Hatul]

To put things in perspective, I regularly teach an OW class to do a 50' CESA (emergency ascent) and my Advanced classes do 100' on one breath of air. If I had a Spare Air, I would feel very comfortable to do a 250' free ascent on a decompression dive to my staged cylinders. Unless I was diving in an overhead environment, there is NO reason why I would need a pony bottle to do a safe ascent (but I have carried a pony many years ago during wreck penetrations).

A number of divers today dive much deeper than they can do an emergency ascent on one breath of air. It doesn't matter if you need two or three breaths to attain the surface by CESA; either a Spare Air or a Pony will give you enough gas. If you want the luxury of breathing all the way and dive relatively deep, a pony is a good choice for you. One has the luxury of more air with a pony, the Spare Air offers less bulk. It comes down to the type of diving you do and what you feel most comfortable with.

When you find yourself in need of air and don't have any, either choice would be a welcome one. Is there anyone diving without a redundant air source that wouldn't welcome a few more breaths of air to get to the surface? Diving in an overhead environment is of course another story.

That sounds pretty scary and dangerous. I think I'll skip your class. I hope you have good insurance.

Adam