AL40 for redundancy diving single tank on deeper dives.

[Bigeclipse]

This topic has been debated many times, to each their own. I would take the time to calculate the amount of gas needed to conservatively ascend from your deepest dives. I use a minute at depth, 30 ft/min ascent, 3 min SS, all at twice your average RMV. A 19 cf pony is what I use on all my solo dives. I sling it on the left. I have a full size SPG and leave the pony on for the dive. I could easily see if I was losing any gas. My cylinder is 1 pound negative, I take a pound off the left side. I think that covers all the usual questions regarding a pony

You are correct but I kind of disagree. Have you calculated your RMV while being frantic? I have seen friends who have RMVs of .3ish but under LARGE stress they jump to over 1. That is over triple. Secondly, recreational limits is 130ft. 19cuft at 130 feet will blow by fast with an RMV of 1. That gives just shy of 4 minutes at that depth before you drain it empty. So let's pretend for some reason you are OOA. You switch to your pony. Now you need to collect your thoughts and make a quick plan in your head. Let's say this takes you 1 minutes. That's 5cuft gone. You now have 14cuft to make a safe ascent and make a 3 minute safety stop. You will likely use 10cuft making your ascent if going 30ft/min leaving you 4cuft to make your safety stop. This was assuming you only needed 1 minute at depth. Sorry but that just doesn't cut it for me. Yes I really like 19cuft for shallower dives of say 75ft and less but anything over that and im using a 40. Just my opinion.

 

[captio2000]

My wife and I have been talking about using an AL 40 as a redundant air supply on some of our deeper dives. Not as stage bottles only for emergency. Have dove doubles and have a set but some boats just too small or not welcome for doubles. We dont want the bracket or anything like that on our tank but to sling it on the side seems the way we want to go. Any do's or donts? when getting tanks or rigging the bottles.

Thanks

I sling an AL40 on the left and really appreciate the fact I am more self-sufficient with it. My kit is more technical than most but I really like having the redundancy and piece of mind. One argument over a fixed pony is you can unclip the whole thing and give it to your buddy.The tank is rigged so it clips onto the left waist D ring and the left shoulder strap D ring. When you get used to diving with it there is really no bother. I suggest you find an instructor that can give you a lesson on use and techniques. Clipping, unclipping, deployment, stowing, dive with valve on or off (on for me) all are discussion point for which advice is warranted.

 

[MXGratefulDiver]

Thanks folks, I've found this thread helpful.

I've been preparing to take the SSI Solo from a friend, and he requires the 40cf pony for the course, if not diving doubles or sm.
Solo, you are your own redundant for everything, including gas. At least in the case of Solo, the pony is NOT for extending your dive time, but for that WTF moment, should it ever happen when there is no buddy to share their gas with you.

I've only slung a pony once, when it was required to dive the Radeaux in Lake George, and i found it awkward. I'm going to find carrying a pony cumbersome, at least at the beginning, but i certainly am willing to learn and adapt.

A properly slung AL40 should not feel awkward ... one of the nice things about the tank is that it tends to ride butt-light, and as such pretty much disappears under your arm. I use one often, both for solo and for some buddy diving, and the only time I ever even notice it's there is when I'm trying to get low to the ground to get a picture ... at which point I have to remember to reach over and lift the top end of the tank up a bit so it doesn't dig into the bottom as I get below those last few inches off the bottom.

... Bob (Grateful Diver)

 

[Scubatude]

Unless carrying my O2 I don't carry anything larger than a 19. But I am curious, what special training does a 40 cf pony require that a 13 does not?

Not special, just consistent. Train with the gear you will dive, especially when diving deeper (or overhead, or deco, or???) dives. A 40 will sit differently, act differently with regard to buoyancy, and be heavier on land. It's not special, just different.

And as always, just my humble opinion. There are many "right" ways is scuba diving. That is one of the things that makes scuba diving great. I was just offering advise per the original post.

 

[MXGratefulDiver]

You are correct but I kind of disagree. Have you calculated your RMV while being frantic? I have seen friends who have RMVs of .3ish but under LARGE stress they jump to over 1. That is over triple. Secondly, recreational limits is 130ft. 19cuft at 130 feet will blow by fast with an RMV of 1. That gives just shy of 4 minutes at that depth before you drain it empty. So let's pretend for some reason you are OOA. You switch to your pony. Now you need to collect your thoughts and make a quick plan in your head. Let's say this takes you 1 minutes. That's 5cuft gone. You now have 14cuft to make a safe ascent and make a 3 minute safety stop. You will likely use 10cuft making your ascent if going 30ft/min leaving you 4cuft to make your safety stop. This was assuming you only needed 1 minute at depth. Sorry but that just doesn't cut it for me. Yes I really like 19cuft for shallower dives of say 75ft and less but anything over that and im using a 40. Just my opinion.

If you're prone to going frantic you really shouldn't be going to 130 feet ... not until you overcome the tendency to lose your cool while underwater. Because you're flirting with bigger issues than just reserve air volume.

That said, if for any reason you feel that a pony bottle of a given size is insufficient for your needs, then by all means get a larger one ... and don't worry about what anyone else thinks about it.

But your argument brings up another point that folks should be considering ... if you're at 130 feet and suddenly go OOA, how much air do you suppose your buddy's going to have available to donate to you? Probably not enough, under the circumstances you describe above, particularly if you're both using those oversize beer cans that they'll typically rent you at most dive destinations.

... Bob (Grateful Diver)

 

[boulderjohn]

A properly slung AL40 should not feel awkward ... one of the nice things about the tank is that it tends to ride butt-light, and as such pretty much disappears under your arm.

A couple technical dive instructors I know used to do something during training dives that the found amusing (but, IMO, not particularly useful from a training point of view). While they were engaged in an assigned activity during the training dive, they would come up behind them, unclip the AL 40, and pull it out from under their arms. The students NEVER noticed. A little later, they would signal the the students to do something with the bottle, and they would be surprised to find it wasn't there.

 

[boulderjohn]

Have you calculated your RMV while being frantic? I have seen friends who have RMVs of .3ish but under LARGE stress they jump to over 1.

I am surprised to find you have friends with 3ish RMVs. I have only known a handful of people with that ability in my life.

I am surprised you have seen so many examples of people in LARGE stress get frantic and triple their RMVs. In all my years of diving, I have only known one diver to get into anything like a LARGE stress, and that diver was in a super extreme situation far, far, far beyond the experience of recreational divers--possibly beyond the imagination of most. You have had some interesting experiences for someone with the number of dives you report.

I am surprised that the people you know with the 3ish RMVs get into such LARGE stress situations, and I am even more surprised that they panic like that. All the divers of that ability I know are not remotely likely to panic. They would all see going OOA at 130 feet while carrying a pony bottle as more of an annoying embarrassment than a reason for panic. The ones I know would not even panic if they didn't have a pony bottle and no buddy in sight--they would just begin a CESA and get to the surface.

 

[Bigeclipse]

I am surprised to find you have friends with 3ish RMVs. I have only known a handful of people with that ability in my life.

I am surprised you have seen so many examples of people in LARGE stress get frantic and triple their RMVs. In all my years of diving, I have only known one diver to get into anything like a LARGE stress, and that diver was in a super extreme situation far, far, far beyond the experience of recreational divers--possibly beyond the imagination of most. You have had some interesting experiences for someone with the number of dives you report.

I am surprised that the people you know with the 3ish RMVs get into such LARGE stress situations, and I am even more surprised that they panic like that. All the divers of that ability I know are not remotely likely to panic. They would all see going OOA at 130 feet while carrying a pony bottle as more of an annoying embarrassment than a reason for panic. The ones I know would not even panic if they didn't have a pony bottle and no buddy in sight--they would just begin a CESA and get to the surface.

Have you not tested your working RMV? I should have clarified, the two buddies that got me into diving/technical diving have .3RMVs resting. Working RMV they are closer to .5. Now one of them did a heavy task load with heavy breathing to simulate a frantic situation and this sky rocketed his RMV close to 1. so to him that indeed made him realize that if something goes drastically wrong, you could triple your RMV.

I am surprised that you (so called really experienced diver) who mocked my last statement, would suggest a CESA is a better plan than bringing a 40 along....

 

[boulderjohn]

I am surprised that you (so called really experienced diver) who mocked my last statement, would suggest a CESA is a better plan than bringing a 40 along....

Where did I say that?

I just said that if someone were in that jam, it is still a situation in which a truly experienced diver will not panic. If I were in that situation, I would certainly prefer an auxiliary air source to a CESA, but I would not be worried if I had to do a CESA. I, context, I was questioning your statement that these superb divers got themselves into LARGE stress situations and became frantic. Your explanation that they actually simulated panic artificially indicates that your initial description was misleading at best.

I recently attended a workshop on diving accidents, and the speaker differentiated between an incident and an emergency. In normal diving, an incident is when something goes wrong, and an emergency is what happens when an incident is mishandled. Going OOA is an incident. Every OW diver has been trained in ways to deal with that incident, so there should not be either panic or a resulting emergency. An emergency happens after the OOA diver holds his or her breath while sprinting to the surface.

 

[uncfnp]

Not special, just consistent. Train with the gear you will dive, especially when diving deeper (or overhead, or deco, or???) dives. A 40 will sit differently, act differently with regard to buoyancy, and be heavier on land. It's not special, just different.

And as always, just my humble opinion. There are many "right" ways is scuba diving. That is one of the things that makes scuba diving great. I was just offering advise per the original post.

Ok. I don't change my rig in any way between bottles. I rig them all the same. So hooking in a 13 vs 19 vs 30 is no different for me. Same procedure to deploy and use as well. Honestly, underwater I couldn't tell you which bottle I had if I didn't already know.

Now on land or a boat...significantly different.