Redundant air with SM configuration

[Bent Benny]

I am diving side mount doubles, usually around 45-65fsw, but sometimes deeper. What is an acceptable amount of redundant air to carry, if any? I have a 3cf spare air that I shouldn't have bought but I didn't know better when I got it. I also have a 19cf pony bottle.

Part of me thinks no redundant air is necessary because I usually don't use all of my gas anyway, but I would like to have my rig set up so that it is ready for the longest and deepest dives I am making.

I know spare air gets alot of hate (for good reason) but I thought in my situation it might be acceptable as it is unlikely that I will bleed both tanks dry before starting my ascent, even in a worse case scenario. Maybe I am not taking something into consideration though so I would like some input.

Thanks for reading and responding.

 

[JohnnyC]

Wait, so you're diving sidemount doubles, and your question is do you need redundant gas, for your already redundant sidemount system? I feel like I'm missing something

Two-tank recreational sidemount is redundant by its very nature. Whether you choose to breathe down one tank and use the other as true redundancy, or whether you switch tanks as you dive, you've still got double the gas of a normal single-tank recreation dive.

What scenario do you think you will find in recreational diving where twice the gas volume is not enough to deal with an emergency.

I'm not trying to rag on you or anything, I really think I'm confused about the configuration you're running. If you're doing recreational dives in sidemount with two tanks, you've already got more redundant gas than most solo courses require.

 

[Bent Benny]

Wait, so you're diving sidemount doubles, and your question is do you need redundant gas, for your already redundant sidemount system? I feel like I'm missing something

Two-tank recreational sidemount is redundant by its very nature. Whether you choose to breathe down one tank and use the other as true redundancy, or whether you switch tanks as you dive, you've still got double the gas of a normal single-tank recreation dive.

What scenario do you think you will find in recreational diving where twice the gas volume is not enough to deal with an emergency.

I'm not trying to rag on you or anything, I really think I'm confused about the configuration you're running. If you're doing recreational dives in sidemount with two tanks, you've already got more redundant gas than most solo courses require.

I thought bringing a pony bottle would be overkill. I just want to make sure I am giving myself the best chance if and when I find myself in a bad situation. I was just thinking of a situation where I breathe one tank down then the reg on the other tank freezes and freeflows or blows a burst disk or something, but even then I would still have a tank with some air.

I just wanted to get some opinions on what would be a reasonable amount of extra air (notice in my op I asked "if any" is necessary)

Thanks for the response. I guess I am just being overly cautious.

 

[northernone]

I thought bringing a pony bottle would be overkill. I just want to make sure I am giving myself the best chance if and when I find myself in a bad situation. I was just thinking of a situation where I breathe one tank down then the reg on the other tank freezes and freeflows or blows a burst disk or something, but even then I would still have a tank with some air.

I just wanted to get some opinions on what would be a reasonable amount of extra air (notice in my op I asked "if any" is necessary)

Thanks for the response. I guess I am just being overly cautious.

Sidemount keep some air in BOTH tanks. Ideally close to equal amounts. Gas management planning is important.

 

[Johanan]

IMO it is not a good practice to breathe down one cylinder completely exactly for the reason you mentioned plus the disbalance will tend to rotate you.. Normally a SM diver uses air for example from 220 to 180 bar in one cylinder, then switches to the other and breathes it to 150. Then goes back to the first one and breathes it to 100, etc. The numbers are not fixed, it’s just an example. Thus, even if you would lose all the air from one cylinder, you will still have a reserve for surfacing. But you can add more cylinders to your system if you plan a longer and/or deeper dive.

 

[tbone1004]

yeah, sidemount is your redundant gas supply. Keep at least 1x of how much it takes you to get to the surface properly in each tank and you're good.

redundant air sources are for catastrophic equipment failures, not failures to plan gas properly

 

[scubadiver888]

I thought bringing a pony bottle would be overkill. I just want to make sure I am giving myself the best chance if and when I find myself in a bad situation. I was just thinking of a situation where I breathe one tank down then the reg on the other tank freezes and freeflows or blows a burst disk or something, but even then I would still have a tank with some air.

I just wanted to get some opinions on what would be a reasonable amount of extra air (notice in my op I asked "if any" is necessary)

Thanks for the response. I guess I am just being overly cautious.

You are being overly cautious. I know people who will dive a single, back mount tank and a pony bottle for redundancy (2 tanks). But if you are diving side mount then you have 2 tanks. Carrying a third tank means additionally task loading. You'll need to practice for using all three tanks. If you get in a stressful situation (one tank fails) then switching to a pony bottle might not be the natural thing to do, unless you train for it.

Additionally, three tanks means you'll need three sets of regulators. I can see over time you might think, in order to save a little money, you won't service the regulator set for the pony bottle. Then if you did need it, it might fail. Or you might even start thinking you can get away with servicing all three regulator sets a little less frequently... then a little less... then a little less... then they all fail and you are in serious trouble.

I'm a strong believer in (a) keep it simple, silly and (b) only get what you really need. Extra equipment isn't going to save you. Knowing how to use the equipment you have will pay off better. That said, NEVER breath down all the air from one tank when diving side mount. Alternate between the two tanks. That is, 500 PSI from first tank, switch, 500 PSI from second tank, switch, 500 PSI from first tank, switch, etc.

 

[Dirty-Dog]

Sidemount is inherently redundant. The way I was trained (and I think this is pretty much standard...) is that you don't breath down either tank. I generally switch about every 500 PSI. If you're staying within recreational limits, and diving double AL80s, you'd have to be one of the biggest air suckers in the history of history to breathe down both tanks. At any given moment, you should have enough air to ascend breathing from one tank, while letting your buddy use the other.

If you do feel the need for a third tank (which, again, seems like massive overkill), toss the spare air in the trash bin and use the pony.

 

[rongoodman]

As long as you have enough gas in each tank to exit to the surface from wherever you are, you have all the redundancy you need.

 

[jerrwhy01]

Read this: Sidemount Gas Management | Sidemount Diving Book it'll help you with managing your gas.