Back mount doubles question

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fraserpenny

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hey everyone. I’m sure this will be a simple answer for you guys.. I’m piecing together a backmount doubles setup and don’t anyone in my area that uses that setup..
my question is.. every time I see a pic of a rig, it appears the wing nut from the tank bands would dig into your back... is this the case or is there something I’m missing?? Thanks
 
It doesn't. It really looks like it is going to be poking you in the back, but the way the backplate is shaped keeps the nut and bolt from making contact with your back.
 
That's not entirely true. A properly set up set of doubles won't dig into your back. Improperly setup doubles could if the person made the bolt too long. Also, Halcyon has the cinch system you can add to their harness. I dove a set of doubles after someone with the cinch set up the tanks and the screw dug in my back.

If you're setting them up yourself and do it right, it shouldn't though.
 
It depends on the bolt length. It can stick out a bit and the shape of the wing will shield your back but if they bolt sticks out too much (2-4") then it could jab you.
 
It depends on the bolt length. It can stick out a bit and the shape of the wing will shield your back but if they bolt sticks out too much (2-4") then it could jab you.

I have a set I have been meaning to replace with shorter bolts, because they do leave marks on my drysuit, and I'm thinking that could cause a hole to wear through in time. I can't feel the bolts, though.
 
Agree with the above. Looks like a problem, but isn't.
I've never had any so long that they were, but I could see that. Not a normal problem.
Humping those tanks wearing a T-shirt and they don't touch. Add a suit and even more space.
 
Awesome!! Looks are deceiving.. and that’s why I wanted to ask..

Seems like a backplate and web harness is the way to go.. I have no idea how much weight i will need, but how do you guys suggest rigging weight up?
 
Awesome!! Looks are deceiving.. and that’s why I wanted to ask..

Seems like a backplate and web harness is the way to go.. I have no idea how much weight i will need, but how do you guys suggest rigging weight up?

Well, if you have a steel backplate, that is about 6 lbs negative. If you are comparing it to a jacket BC, many of them are a pound or two positive from the padding, so there is that difference if you were using your BP/W with a single tank.

If you are diving steel doubles and a steel backplate, you may not need any weight at all. I never did, even in a dry suit with thick undergarments.

If you are diving with double aluminum 80s, you might need to do a weight check and add ballast. I have only done that once, in a 5 mm wetsuit, and I needed 6 lbs.

As far as where to put weight if you need it, you need to decide if you must have ditchable weight or if you are OK with trim weight. If you don't need ditchable weight, many people use V-weights - either cast lead or a pouch to which you can add weight. These fit between the doubles and are held in place by the bolts. That's what I used when I was using the double AL80s. I was OK with non-ditchable weight, since I had a relatively thin exposure suit, and didn't need much extra ballast. I figured I could swim up the 6 lbs if necessary. This topic is a common debate here, and there are lots of threads about it.

You will find that most tech divers don't use ditchable weight for a few reasons. First of all, with doubles you generally don't need huge amounts of additional ballast, and you are generally carrying one if not two SMBs. So even if you don't have a dry suit and you have a total wing failure, you could swim your rig up without ditching weight. And if you had to, you could use an SMB for backup buoyancy.

Also, tech divers are wary of anything that could accidentally make them suddenly buoyant, like dropping a weight. If you have a deco obligation, a sudden increases of buoyancy could be life threatening (this may have happened recently on the Andrea Doria).

Can you tell us more about what kind of tanks and exposure suit you will be using?
 
Thanks for all the info doctormike!!
I was curious if I would even need any weight...
I have steel 100’s doubled up and dive an aqualung fusion bullet..
I have been diving an apeks wtx harness bp/w. I wasn’t sure what was the best rig to use for the doubles. Use the wtx as well or just pick up a webbed harness for the backplate...
 
Not familiar with the Apeks, but it looks like you can add a steel backplate to it for mounting doubles.

I like a clean, plain steel backplate with webbing, but if you already have the Apeks and if you can use a standard backplate with it to try it out, I don't see the problem with trying it out. No reason to spend more money if that will work. Maybe someone with experience diving the Apeks can chime in...?

With steel doubles you shouldn't need much additional weight, if any. Can always do a weight check!
 
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