Going with Doubles

[Bowers]

Does the math on this actually check out? 500psi in a set of doubles will be double the gas in a single tank that has 500psi (assuming all are the same size). So if you’re getting out of the water on dive two with the set of doubles at 500psi you didn’t actually get any extra gas. However if you had to breathe it down in an emergency then yes you have a larger buffer on the doubles.

Why do you have to get out with the same psi? If you’re ok with diving until say 10cf on a particular dive, then you should be fine doing a dive to the the same parameters with doubles ending in the same volume (ie half the psi if same sized tanks).
So on single tank, dive one ends with 10 cf. then dive two ends with 10 cf. thats a total of 20 cf unused.
Whereas with twinset, dive one ends, tanks stay on and dive two ends with 10 cf. thats a total of 10cf unused with same number of dives.

Also i would argue that if trained correctly, the redundancy aspect beats single tank and is more comfortable in the water than adding a pony.

 

[-JD-]

@Jason McK,

You might borrow a set of double steel 119's first to try them out.

I really enjoyed diving a single HP 100. But when I moved to double HP 100's, I learned that I could not easily reach my manifold valves. I liked everything about these 7.25" OD double 100's (capacity for the types of dives I would be doing, buoyancy, out-of-water weight, etc.), but the fact that I couldn't easily reach my valves was always a concern.

Eventually, when I began considering doing longer, deeper exposures, I switched to double HP 120's. These 4"-taller cylinders made reaching my valves much, much easier.

BTW, at the time (1998), LP 85's weren't available. I think now that I might have considered double LP 85's (rather than double HP 100's) if they had been available.

ETA. Several years ago I broke apart my double HP 120's probably permanently. Paradoxically, a single HP 120 is too tall for me to dive comfortably as a single tank. As mentioned, my HP 100's were perfect for this, though.

rx7diver

I've got a pile of 100s and 120s but only one set of 100s are banded up so far.

I'm curious, why not shift the 100s higher? Either higher holes on the plate or by shifting the bands down on the tanks?

Were you referencing the bands based off of the bottoms or the shoulders?

 

[rx7diver]

I'm curious, why not shift the 100s higher? Either higher holes on the plate or by shifting the bands down on the tanks?

Moving the HP 100's higher made me head-heavy, wanted to face-plant me. With the cylinders sitting at perfect, effortless balance, and the backplate sitting comfortably, the manifold knobs were just barely out of comfortable reach. I could reach them, of course, but only with effort.

The 4"-taller HP 120's allowed me to move the cylinders, effectively, about 1.5 inches higher--which kept the perfect, effortless balance, while making for effortlessly reaching my valves. I am 6'2".

One other thing: The HP 100 doubles were too short for me to "sit" well. That is, when I was seated on a bench and wearing the HP 100 doubles, the doubles were not resting on the bench! I imagine that if I had had to wait a long time for my turn to splash, this would have been quite uncomfortable. The HP 120 doubles sit when I, myself, sit!

But, I really liked my HP 100's. So much so, that I called my old Michigan dive buddies a couple of weeks ago trying to reclaim my old tanks. Alas, they had long ago been traded away.

rx7diver

 

[NothingClever]

I want to fleet up from my AL80 twinset to get longer BTs without having to add a stage and so naturally started looking at HP100s. Just today I got a vetted recommendation to check out a twinset of LP85s so still in the hunt.

 

[Jason McK]

Thank you all, Good idea's and thoughts.
I guess boubleing the 119 is just so I don't have to purchase new tanks. But I see steel 100 around the used market a lot so I may wait and pick up some 100s

 

[Jason McK]

Those are fairly common around here......more than enough air for a couple of dives......are you thinking of taking an intro course or do you have an experienced mentor?

Yes I'll take a orientation course. My LDS instructors all use doubles

 

[Bierstadt]

I have a set of lp112 doubles. Every time I pick them up I ask why I must punish myself this way - they weigh 100lbs, plus plate. The answer is that I need the gas, but a single lp112 and an al40 pony was much more comfortable for me. But the gas management advantages to doubles are undeniable. As are the preferences of the many divers who love their doubles. I would recommend jumping into the orientation course so you can try a couple instructor rigs before you invest in doubling hp119's or buying a set of hp120's, hp100's, lp104/8/12's, etc, as well as getting that in-person opinion on the best tanks for your gas needs and body.

 

[DogDiver]

E-119’s are ball busters as backmount doubles. Way too negative and unless your 6 feet tall you will be hitting your legs on them. In fact if diving them you better have a redundant air cell or they may kill you. But, I cave dive them sidemount and underwater they have the same buoyancy as sidemount 85’s. But I also use a drysuit and large capacity Nomad to keep me neutral.

 

[Rose Robinson]

Hi All,
Don't post much, but have always enjoyed reading on Scubaboard
I'm a cold water diver with steel 119 and thinking of going with a doubles set up.
I already dive a backplate. So my question in do you think the steel 119 would be too heavy a load.?
Mine a bit of a air vacumn so I'd like to be able to do 2 30~45 minute dives with the Doubles

Thank you
J

Hi Jason,

I'm on the Island.

I have two sets of double HP steel 80's, recent Fabers.

I dive to 150', and depending on the dive, sling one or two 3AL 40's.

For two tank dives, I bring both sets.

HP 8'' 117's/119's are big/heavy. For 45 min. dives to 130' you should have plenty of gas diving your single 119's, especially if you're slinging a small bottle, 30/40/LP steel 50.

It's a quick switch back on the boat, and with your surface interval, you have lots of time.

If you're over-draining your singles, and following your typical single tank depth/time using doubles, you are not necessarily going to end up with more gas reserve, remembering, you may need additional gas to keep you neutral with doubles, especially important if you should run into trouble.

Assuming you're diving dry, if you're diving wet, and want to switch to doubles, you will also need to consider a redundant bladder wing.

Hope this helps.

Rose.

 

[PfcAJ]

E-119’s are ball busters as backmount doubles. Way too negative and unless your 6 feet tall you will be hitting your legs on them. In fact if diving them you better have a redundant air cell or they may kill you. But, I cave dive them sidemount and underwater they have the same buoyancy as sidemount 85’s. But I also use a drysuit and large capacity Nomad to keep me neutral.

119s are the same size as 95s.