Going with Doubles

[Jason McK]

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

 

[Bowers]

119s are heavy doubles. Id suggest lp108s for better weight and still lots of air. I personally like the 85s best but you’ll need to determine if thats enough air for a vacuum to do two dives.

 

[dberry]

If your 119s are E-8 119s like mine, be aware that the 8" bands won't work with many other tanks you might want to pair up some day. And yes, a pair of those will make a very heavy twinset.

 

[grf88]

If the objective is to do two dives rather than longer dives why not stick with singles and save your back and knees.

 

[Coztick]

If the objective is to do two dives rather than longer dives why not stick with singles and save your back and knees.

Right?
A second tank, won't have to match...
If the point of moving to doubles is redundancy, sling a smallish pony.

 

[decompression]

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?

 

[stuartv]

If the objective is to do two dives rather than longer dives why not stick with singles and save your back and knees.

If you finish your first dive with 500 psi left in your single tank, that air is of no use to you on your second dive.

If you finish your first dive having used the exact same amount of air, but out of a set of doubles, then the reserve that you have leftover is there to use during your second dive.

E.g. dive with 120s as singles. Finish your first dive having used 100 cu-ft, so 20 cu-ft left in the tank. Start second dive with 120 cu-ft available.

Do the same 2 dives with doubles. Finish your first dive having breathed 100 cu-ft. Start the second dive with 140 cu-ft available.

With doubles, you have LOADS of extra gas for safety during the first dive. During the second dive, you still have a lot more safety margin than diving with a single tank.

To me, doubles are a lot more pleasant in the water than a single tank and slinging a pony.

I dive double steel 120s. I dive them any time I'm diving OC, if at all possible. They're heavy, but the weight is not a problem for me or a lot of other people.

 

[tha_ton]

If you finish your first dive with 500 psi left in your single tank, that air is of no use to you on your second dive.

If you finish your first dive having used the exact same amount of air, but out of a set of doubles, then the reserve that you have leftover is there to use during your second dive.

E.g. dive with 120s as singles. Finish your first dive having used 100 cu-ft, so 20 cu-ft left in the tank. Start second dive with 120 cu-ft available.

Do the same 2 dives with doubles. Finish your first dive having breathed 100 cu-ft. Start the second dive with 140 cu-ft available.

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.

 

[stuartv]

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.

Isn't that what I said?

Again: If you use a single tank, any gas left in it is gas you can't use on your second dive. With doubles, that leftover gas would still be able to be used on your second dive.

 

[rx7diver]

I'm a cold water diver with steel 119 and thinking of going with a doubles set up.

@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