Independent backmount doubles with DSS backplate

[2airishuman]

I have an older DSS backplate and doubles wing that has the cutouts for cam bands for independent doubles.

I decided to try this configuration for two dives a couple days ago. First dive with two LP72s, second dive was a night dive, and I swapped out one of the LP72s for an LP85:

I used SPGs of contrasting color and size. The larger one with the white background is my usual SPG, and was on the right post, and the smaller one with the black background was on the left post. Other than the extra SPG, the assignment of hoses to posts was DIR.

The configuration dived well, with several practical benefits over banded manifolded doubles:

1) No need to dedicate cylinders to a twinset, can dive singles when appropriate and use the same cylinders for doubles
2) Can swap out a single cylinder after a dive if that makes sense under the circumstances
3) Could use rental cylinders without having to seek out a shop that has a twinset for rent
4) Easier handling of cylinders for transport and filling without the weight and bulk of a twinset

The main drawback that I encountered is that the process of attaching the cylinders was somewhat awkward compared to either a single cylinder (where I can lift the BC with one hand and handle the camband with the other) or a banded twinset.

I am not sure whether I would be comfortable with a single camband securing a larger cylinder (e.g. HP120) in place.

 

[CuzzA]

I suppose gas management between the two tanks needs to be taken into consideration to avoid rolling and your buddy's emergency gas supply, much like side mount diving.

 

[BoltSnap]

What about your ability to reach the valve on the left tank and be able to turn it off and on, can you do it underwater no problem?

 

[BoltSnap]

I swapped out one of the LP72s for an LP85:

Did you have two dissimilar tanks on the BC? Did it cause any issues in any way at all?

 

[tbone1004]

@CuzzA because the doubles are much closer to your centerline than sidemount, the moment arm is much smaller and you can actually dive a pretty wide swing in tank pressures/volumes without significant impact on your roll stability.

@BurhanMuntasser 72's and 85's should be same diameter so the only inconvenience would be trying to sit the gear on something since the 85's are longer. The normal valve on the left doesn't really lend itself to being shut off as easily, but it's in a similar position to the isolator manifold so you could get it off if you had to. I dive indy doubles regularly though my plates from DSS don't have the cutouts so I use a set of independent doubles bands. One of the nice things with them is to dive similar to the way he mentioned by rotating between 3 tanks. Use left tank for ascent/descent, and right tank for the first dive. Pull the right tank out and swap in a new one and repeat the process and you have essentially a mounted pony bottle on the left hand side with ample gas reserves. For a 3 tank dive you follow basically the same procedure and you can bleed the last two bottles down evenly for the final dive.

@CuzzA only differences I have are using 4x cam bands to make sure stability is as good as it can be, and then I put the spg's on their respective sides. Easier for me that way since they are the same length and just go down and back up and also allows familiarity with my sidemount setup

 

[Basking Ridge Diver]

I suppose gas management between the two tanks needs to be taken into consideration to avoid rolling and your buddy's emergency gas supply, much like side mount diving.

You would think but it is not...

I have dove Side mount (72s) you need to swap regs every 400 or 600 PSI or thereabouts... With Back mount you can drain it right down to 1000 or less on one tank and not notice the other is full. I dove this weekend with steel 72s and I was surprised how little difference it made - as well I like the redundancy. I have manifolds as well - so I am still struggling which way I like better - manifolded or IDs.

For me - it may come down to filling singles is easier for me than twins - I can not fit the twins in the containment box so I have to fill them out side the cascade housing...

 

[Nemrod]

My independent doubles are banded steel 72s on a Hammerhead plate. I may reverse the left tank or flip it for valve access with a low profile first like a MkV. N

 

[CuzzA]

Good to know. So, since this configuration, like side mount only uses a single second stage per tank do you keep a reserve in either tank for a buddy? What's the air sharing procedure?

 

[tbone1004]

basically the same as sidemount. I have a 7' hose on the right bottle and will donate that whether it is in my mouth or not. Reserves are set in either tank as part of rock bottom calculations. I leave 1000psi in an AL80 or LP72, and that goes up or down depending on what tanks are being used

 

[BoltSnap]

72's and 85's should be same diameter

Thanks. I actually read it as an AL80 and didn't see that it was an 85 until I read your comment. It didn't make any sense to me at first