How do you mount your deco cylinders, on top or below? And why do you do this?
Sidemount Deco Cylinders - top or bottom mounted?
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JamesK
Contributor
Bottom. That way I can easily confirm the gas in it. Stages go on top because it is always the same mix as my main tanks. Also, my deco bottle gets dropped anyways and a front/bottom mount is easy for me.
bamafan
Contributor
I think that the safest thing to do is hang your deco mixes underneath. They are alot easier to verify that you have the correct bottle there. But, I just got back from a trip to Truk Lagoon and I took my SMS 100 so I was diving sidemount on the Odyssey. They wanted $2 / cuft for anything above 40% so I dove air on the deeper wrecks and took 1-2 aluminum 80's backmounted as stages as that was all I had with me for stage kits. I didn't really feel this was unsafe because I was only diving air in my sidemount tanks and 40% in the backmounted stages so there was only 1 gas switch and it is easy to trace the reg back to the backmounted stages. I also kept the regs stowed / clipped off to the valve on the stages still I started my ascent. The only dive I did using 100% O2 was the Oite and this was with a 30 cuft bottle slung underneath. As far as cave diving goes you generally are dropping them and not swimming very far with your deco cylinders so having them underneath in my opinion is the safest way to do it. Oh by the way if you haven't been to Truk Lagoon it is definately worth it.
I top mount my bottles. Their MOD is marked at the top of the bottle for my verification and at the bottom in the classic place for my partners verification. I find they ride better top mounted, i find bottom mounted bottles to be clumsy. I just dive open water, no caves yet.
Kevrumbo
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I dive the the UTD Z-system doubles sidemount -the long hose primary regulator breathing the bottom mix always stays in my mouth in normal non-contingency diving, and I only switch regulators when I change to deco gases. I use dedicated conventional deco regs, and do not "plug-in" deco mixes via QC6 connectors of the Z-system.
"Right Rich" O2 deco bottle AL40 clipped above right bottom mix sidemount tank AL80; "Left Lean" 50% deco bottle clipped above the left sidemount tank. In Truk Lagoon, I usually drop my deco tanks outside the wreck near the upline before penetrating, and pick them up upon egress & clip them off in the right rich, left lean configuration for better balancing.
"Right Rich" O2 deco bottle AL40 clipped above right bottom mix sidemount tank AL80; "Left Lean" 50% deco bottle clipped above the left sidemount tank. In Truk Lagoon, I usually drop my deco tanks outside the wreck near the upline before penetrating, and pick them up upon egress & clip them off in the right rich, left lean configuration for better balancing.
Top.
Ditto.Kevrumbo:
Why? Because that (top) was the way I first learned sidemount deco, and never found a good reason to change. So, it may be a matter of (overcoming) inertia as much as optimal placement.
Top, right rich, left lean. I carry 4 deco bottles (alum 80s) on 300+ft dives without issues. Gas mixes are marked top and sides for verification on my part and for other team members. Why? I'm comfortable with this configuration and it works for me.
hi will be doing a side mount course in april with the sms 50. and been scanning this " side mount subform" for a while. i have looked on google but i have not been able to see any images of the difference between mounting tankson the top or bottom, could some one post some images or explain the difference 
thanks
thanks
OP
This is a cylinder filled with bottom mix, not a deco cylinder, but it should give you an idea of top mounting tanks. Keep in mind that most people's stages don't trim out that well.
Most look like this:
Most look like this:
Karl_H
Contributor
I’d be another vote for the deco bottles mounted on the bottom with a rich right, lean left configuration. I dive independent sidemount tanks so trapping the long hose is less of an issue with the right deco bottle as the hose is bunged against the tank rather than routed around the hip.
My deco tanks tend to have a very tight clip attachment at the neck and a little more movement at the tail so that then work well in backmount, when positioned below the main tanks the deco tanks can’t trim upwards as they are held in place by the upper tanks, it’s important to start the dive with the deco tanks on the upper harness d-rings rather than the from d-rings (in a razor style harness) as otherwise the deco tanks hang too low, if they are attached to the upper d-ring they tend to be positioned well and as they become buoyant they are held snugly in place by the main sidemount bottom gas tanks.
In backmount I put all my deco tanks on the left with the richest gas at the bottom, I like to keep the same principle in sidemount so keeping my deco tanks on the bottom means the leanest gas is still on the top. For big dives I’d either use CCR or backmount unless sidemount was essential so it’s rare I’d need additional tanks.
My deco tanks tend to have a very tight clip attachment at the neck and a little more movement at the tail so that then work well in backmount, when positioned below the main tanks the deco tanks can’t trim upwards as they are held in place by the upper tanks, it’s important to start the dive with the deco tanks on the upper harness d-rings rather than the from d-rings (in a razor style harness) as otherwise the deco tanks hang too low, if they are attached to the upper d-ring they tend to be positioned well and as they become buoyant they are held snugly in place by the main sidemount bottom gas tanks.
In backmount I put all my deco tanks on the left with the richest gas at the bottom, I like to keep the same principle in sidemount so keeping my deco tanks on the bottom means the leanest gas is still on the top. For big dives I’d either use CCR or backmount unless sidemount was essential so it’s rare I’d need additional tanks.
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