Sidemounts versus Twin Tanks On The Back

[Marie13]

Sidemount is far more flexible than backmount. This flexibility comes at a small cost of faffing around to clip the kit together. Practice solves that.

One benefit of sidemount is being able to split the cylinders from the rig, both underwater or for carrying to the site. It’s so much easier to throw a single cylinder over your shoulder and carry it up/down the beach or over the mountain.

Other benefits of sidemount are the comfort and trim from not having a massive weight on your back. Access to the cylinder valves is so much easier, similarly seeing all hoses and regulators rather than groping around behind your head.

If diving alone, sidemount is far superior to backmount.

And if you’ve got bubbles coming from somewhere, you can see them!

 

[steinbil]

So, let me explore this a bit, because I have had doubts about this concept since I started diving.

BM doubles with an isolator provides redundancy against equipment failure (reg, valve or O-ring), but not an OOG situation because you can consume all your air without having to take a physical action (pull a reserve, switch regs, etc).

A larger single tank plus a pony, or diving sidemount, provides redundancy against both equipment failure and (mostly) against human error. It is more redundant because you have to take some physical action to use up all your air. It's possible that someone could take that action without recognizing its implications, but that seems unlikely.

So, ir seems to me that Non-isolated doubles with an adequate pony would be better than isolatable doubles without.

Fundamentally, it comes down to what is most likely to fail, the hardware or the squishy part between the ears? Once someone answers that question, then they can start mitigating the hazard they feel is more significant.

To run out of gas, you have to make a thousand errors. Not just one. It should simply never happen. (1) You should plan your gas according to the planned exposure. (2) You should pay attention to your time spent and depth to follow your plan. (3) You should know how much air you breathe (SAC rate) and be able to estimate gas usage underway. (4) You should regularily check your SPG to confirm your estimated gas usage. Depending on the circumstances, and your experience, as often as every 5 minutes. (5) You should plan to have a gas reserve, so overshooting that is already a grave mistake, but then you still have the reserve to cover your mistake.

If you run out of gas (disregarding equipment malfunction), you have failed all of these, and that shows more complacency and an unsafe practice than it shows the margin of human error.

 

[Angelo Farina]

When I started, in the seventies, it was always twin tanks on the back.
At that time it was normal to dive at 50-55m in air and to do 15-20 minutes of deco, so a twin tank was mandatory.
With two regs on two separate valves.
And for the more extreme dives we added a pony tank.
Growing up and getting older, I reduced max depth (40÷42m) and deco time (10÷15 min), so I found the sweet spot with a single tank, steel, 15 liters.
Still double valves and two fully independent regs.
Charged at 232 bars you have almost the same gas as the back mounted twins (these were typically 9+9 or 10+10 liters at 200 bars), but a single tank is much cheaper, both at purchase and at hydros. And also in some filling stations.
I have little experience with side mount, used it just a couple of times, and found it much more complex and less practical than backmount.
So my suggestion is to stay with a single back mounted, just get rid of the crap AL80 and use a 15 liters steel at 232 bars (which I do not know how is labelled in cuft).
So you can keep all other equipment unchanged (regs, BCD, etc ).
If you want more redundancy, get a tank with double valves.
This is plenty enough for recreational diving, even deep (40m) and with light deco (10 min).
In almost every places I had dived these 15 liters steel tanks were easily available on request, or even the standard ones for everyone.

 

[Cthippo]

To run out of gas, you have to make a thousand errors. Not just one. It should simply never happen. (1) You should plan your gas according to the planned exposure. (2) You should pay attention to your time spent and depth to follow your plan. (3) You should know how much air you breathe (SAC rate) and be able to estimate gas usage underway. (4) You should regularily check your SPG to confirm your estimated gas usage. Depending on the circumstances, and your experience, as often as every 5 minutes. (5) You should plan to have a gas reserve, so overshooting that is already a grave mistake, but then you still have the reserve to cover your mistake.

If you run out of gas (disregarding equipment malfunction), you have failed all of these, and that shows more complacency and an unsafe practice than it shows the margin of human error.

And yet people do ot every day. I have not seen research on it, but I suspect that OOG accidents are far more common than equopment failure ones.

 

[steinbil]

And yet people do ot every day. I have not seen research on it, but I suspect that OOG accidents are far more common than equopment failure ones.

Yes, because of unsafe diving practices, poor instruction and complacency.

 

[Celt]

I want more bottom time so I’m trying to decide between sidemounts and twin tanks using a manifold on my back.

At the risk of sounding snarky, let me be clear. I have hundreds of dives under my (weight) belt. I’ve very comfortable under water, I frog kick, I’ve done technical diving and I’m certified in cavern and caves. In the latter, I dove with twin steels. In other words, I don’t need to hear “you just need more dives so you feel comfortable, then you won’t need multiple tanks.” O.K. off my soapbox.

From here on, my dives will be recreational and open water. In other words, no caves or technical wrecks. On an aluminum 80 I get 40 – 45 minutes at best. Either way I go it’s going to cost me money. Here are some pros and cons.

Twin Back Mounts On A Manifold

Pros: - I have experience with them.
-I can use my existing regulator.

Cons: - Need a backplate, wings, and a manifold.
- Heavy on my back.

Sidemounts

Pros: - Easier on the back
-Perhaps a little more flexible???
-Easier to maneuver on a small boat.

Cons: - Need certification
- Need sidemount BC, additional regulator, hoses etc.

Am I missing anything? For those that have done both, which do you prefer and why?

Thanks!

If you’re happy carrying a twin set, then back mounted twinset is half the hassle of side mounting. And a lot more secure.

 

[VikingDives]

If you’re happy carrying a twin set, then back mounted twinset is half the hassle of side mounting. And a lot more secure.

and half as advantageous when a problem occurs.

 

[grantmac]

In sidemount you can easily connect or disconnect anything: BCD, drysuit, you name it.
Fall over in shallow water or drop off the side with the tank valves off and the valve is right there, that's killed people.
The only time doubles are better is a reg freeflow but feathering a reg is a basic sidemount skill. You can literally swap regs in the water if things get really desperate.
On a vacation you can choose to dive a single or doubles with any tank on the rack. You can use any form of weights available. No need for custom spine or tail weights.

I've never been the last diver geared up on a boat or shore dive because of being in sidemount.

 

[Wibble]

Oh, the memory of climbing Dinas "mountain" with a twinset as opposed to spreading the load with sidemount…. Have to carry your kit about 800m/2500ft over a 60m/200ft steep hill.

UK geology really sucks for underground diving opportunities.

 

[Celt]

Oh, the memory of climbing Dinas "mountain" with a twinset as opposed to spreading the load with sidemount…. Have to carry your kit about 800m/2500ft over a 60m/200ft steep hill.

View attachment 806908

UK geology really sucks for underground diving opportunities.

How could doing it twice with the tank hanging loose be easier. Side mount is an absolute pain on land, and the only time its comfortably in the water is horizontal back up. A low ceiling is the only in water advantage of side mount over back mount . In water you’re constantly fiddling with your gear in side mount, loose tanks changing buoyancy as they empty, there’s nothing worse than something loose hanging off you when diving. I tried it for two years because I believed it would help with the weight of the twinset but it caused more hassle than it solved. The amount of hoses alone is a pain and they have to be an exact length. I sold the whole lot and went back to the simple, clean, back mounted twinset, a pleasure to dive in.