Double Tank Manifolds, Bad Idea!

[Rich Keller]

I have slung bottles but never used any of the new side-mount rigs. I don’t understand the mechanics of how the weight distribution to the shoulders using a side-mount is different than back-mount. I understand the lower center of gravity on deck, but the weight transfer to the shoulders and spine look the same. Am I missing something?

No expert here, but I can see an advantage for a lot of divers with spine-related limitations if all or part of the weight could be transferred to the hips and legs. This is easier said than done with a disappearing-butt male geezer like me, but it looks doable for divers with more pronounced hips. This would not necessarily be a tech-rig but more likely side-mounting independent 30s or 40s. Leg straps for weight transfer and stabilizing might work well on the some amputees and paraplegics.

I have never used side-mount but the only other advantage I can see besides a lower center of gravity is having the tanks on either side balance the load rather then having the whole load behind you. This will not in any way reduce the overall weight though and having them hanging at your sides would seem to me to make it more awkward to walk on the surface. The idea of attaching the tanks while you are hanging off the back of a boat seems like a real bad idea, as it is most sport divers carry way too much equipment hung everywhere and adding slung tanks to that mess would make things worse in my opinion.

 

[mathauck0814]

I have never used side-mount but the only other advantage I can see besides a lower center of gravity is having the tanks on either side balance the load rather then having the whole load behind you. This will not in any way reduce the overall weight though and having them hanging at your sides would seem to me to make it more awkward to walk on the surface. The idea of attaching the tanks while you are hanging off the back of a boat seems like a real bad idea, as it is most sport divers carry way too much equipment hung everywhere and adding slung tanks to that mess would make things worse in my opinion.

For all intents and purposes, aluminum tanks are neutral in the water and don't create "ballast" that needs to be balanced. SM has a distinct advantage of clearing up the chest area that can be cluttered with other essential equipment for a dive. It also reduces drag by allowing tanks to swim through the water with the lowest profile (whereas slinging them creates a good amount of drag).

I've never been a big fan (personally) of sidemounting primary gas, but for carrying lots of stages and deco bottles or bailout, it's a pretty slick alternative.

When it comes to attaching bottles - it comes with time and practice, like anything else.

 

[TSandM]

I'm surprised at the folks who say that sidemount cleans up your chest. I have the opposite feeling about it -- by the time I've brought the inflator across my chest and have my bungied backup under my chin, and the two inflator hoses, I feel as though my chest is much more cluttered than it is in backmount.

 

[mathauck0814]

I'm surprised at the folks who say that sidemount cleans up your chest. I have the opposite feeling about it -- by the time I've brought the inflator across my chest and have my bungied backup under my chin, and the two inflator hoses, I feel as though my chest is much more cluttered than it is in backmount.

It's probably relative. But with two SPGs, two MAVs, backup lights, primary light head and primary inflator all over your shoulder or on the chest D-rings, adding four more nose-snaps is a lot of crap. Moving that stuff down a few inches helps me a lot. Plus there's less drag on the scooter

 

[Akimbo]

...Plus there's less drag on the scooter

I don't understand the physics behind that. The head-on profile area is the same and possibly worse when side-mount cylinders aren't aligned to the body as well as back-mount. This is not a criticism or promotion of one or the other, just a question of hydrodynamics.

 

[mathauck0814]

I don't understand the physics behind that. The head-on profile area is the same and possibly worse when side-mount cylinders aren't aligned to the body as well as back-mount. This is not a criticism or promotion of one or the other, just a question of hydrodynamics.

My assertion was side mounting vs. slinging to create less drag. Either way I'm back mounting either doubles or a rebreather which (if trimmed appropriately) should have a low drag profile.

 

[Akimbo]

I have never used side-mount but the only other advantage I can see besides a lower center of gravity is having the tanks on either side balance the load rather then having the whole load behind you...

Good point. That might be a factor for some back problems. This discussion has me thinking of a modified side-mount that would shift weight to the hips and legs for people with that limitation. The market is too small for a manufacturer to make but a DIY project isn’t out of the question for someone with a small shop or maybe turning over to a sail shop. Maybe I’ll take this over to the disabilities forum to solicit ideas.

…Slung bottles to me are a curse. I loath them…

Me too. Slung bottles are a very last resort for me.

---------- Post added September 22nd, 2013 at 09:24 AM ----------

My assertion was side mounting vs. slinging to create less drag...

Now I get it, agreed.

 

[DaleC]

My experience so are with SM vs BM is:
BM = a larger vertical profile. SM = a more horizontal profile.
BM = more prep at the car (or wherever you suit up). SM = more prep in the water (connecting hoses).
SM = better resting initial stability in the horizontal plane but a diver with good skills can achieve the same in BM.
SM = better access to valves but less access to the lower center of the abdomen.

I chickened out on going SM on a recent dive trip because I was concerned about the boat. As it turned out it was a skiff that was hard to BM from (the benches were too low) and would have been awesome to SM from (easy to clip in on board and a big ladder for exits). Other boats I have been on have small rear doorways that might make SM transit a PITA.

 

[shoredivr]

The point that I was trying to illustrate is that back mounted manifolded doubles are very versatile. IMHO they are better suited for doing a dive to the Gunilda than sidemount or back mounted IDs. In the sidemount case are you going to leave valuable real estate unused when you need to carry that many cylinders?

It just takes practice. Razor harness wouldn't be sufficient for the cold water of the Gunilda, but you get the idea.
Multi Stage Dive by Steve Bogaerts with the new Razor Side Mount System - YouTube

 

[Slamfire]

It just takes practice. Razor harness wouldn't be sufficient for the cold water of the Gunilda, but you get the idea.
Multi Stage Dive by Steve Bogaerts with the new Razor Side Mount System - YouTube

I guess if you had to, you can find a way to get to the Gunilda on sidemount and then back. But your arms and hands are very valuable tools. You leave your back totally clean at the expense of cluttering the space used for the range of motion of arms and hands. How comfortable will it be to operate a video camera rig when you have six tanks all around your thorax with the exception of your back--where your arms and hands are useless for the task. If you don't need to squeeze through tiny openings you might as well use the prime real estate on your back to keep tanks out of the way. One of the reasons why I like to carry a leash, even when I'm slinging only one tank, is because after I'm done with the stage, I just move that floaty bottle out of the way and enjoy more freedom of movement.

As I said before, there are very valid reasons for sidemounting like vertebrae, difficulty to move tanks through rough terrain, etc. I wouldn't venture to throw a wide blanket statement saying sidemount is a bad idea. But, if you can still lift doubles and use the real estate on your back, why wouldn't you?

The one thing that jumps at me every time I open this thread is its title. After all 13 pages of discussion I cannot see why manifolded doubles are a universally bad idea. Their ubiquity seems to point to the contrary.