Which tank sizes are commonly used for doubles?

[Dive-aholic]

Rent/borrow some different sets of doubles before you go spending money on more tanks. I'm 6' 200lbs +/- (usually +). I started out in 95s. They worked for me, but were probably a little too short (although I do still dive 95s without problems). I've also used 85s and been very happy with them. In fact, when I dive backmount, it's my set of choice right now. I have also used 108s. They worked well with my crushed neoprene dry suit, but are not easy to trim out in my trilam and I definitely won't dive them wet. They are just too heavy and too bulky and cause my consumption to increased by 1/3 more over 85s. I can do the same dive on less gas in 85s than on 108s.

As for adding a deco bottle, don't do that until you have the proper training.

 

[IceBergSlim]

That would depend on a whole bunch of factors. There is no ideal choice for everyone.

What is your RMV? What kind of diving do you plan to do? (no matter what you say now you will most likely change your mind in a few months/ years)

What do your buds require in both a share gas situation as well as a need to borrow?

What do you feel comfortable climbing the ladder with? Add high seas and subtract from the previous weight.

How big is your car? Do you plan on doing two dive per set or one?

Do you have access to a "band bending overfill" or is your local fill station nervous nellies? The list is pretty endless.

For the record I am XXL and have a decent RMV cosidering my size. I almost always dive solo.
I own 121's, 108's, 104's, 85's and 80's. All steel LP of course.

The 121's are stupid heavy but often I need all that juice. The 85's are great for most general dives.

Lastly, keep your 130 as a single and buy some used doubles in a size you feel ok with now. Used is the best way to go.

 

[imasinker]

Thanks Icebergslim, I think i will go with the lighter tanks, and as for the previous reply Dive-Aholic, i do fully intend on the proper training, as i stated i will be taking the intro to tech and on from there. I was just curious as to what other divers find easier to manage as far as size and weight. Thanks all for the great responses.

Rob

 

[sharky001]

I use LP108's, which are the same size as your 130's, and the only other size tanks I'd look at are Faber LP85's (I think there's a HP100 equivalent to this tank, too) due to their light weight.

I second this, LP 85s or even 100s would be ideal for doubles. I have 2x Faber 125s [though I've never doubled them]. As others have said the problem is weight. I find lugging a single LP 125 around is difficult enough at nearly 60 lbs full. A doubled set of LP 130s, man I couldn't imagine getting those to the dive boat or lowering them off a wharf. Maybe if they were on a shipping pallet or something. Once in the water they'd be fine, but at the surface they would definitely suck. 100s would be as big as I'd go for everything but the most extreme diving. My current pet project is build a set of double lp 45s ... great for winter diving or trips where you want redundancy, but manageable weight. Good luck ... let us know what you decide.

 

[Papa_Bear]

Hi everyone, Hope you all are having a great dive season.

I am sure it has been asked and I would like to know what most of you use for doubles and in tank size. I am making the move to doubles this winter. I have a faber 130 and was thinking should I double it or down size to smaller tanks. I have seen some use these and weigh doesn't seem to be an isue. I am 6'2 and using a OMS set up with S/S BP and harness. What are the sizes most commonly used or favored? Opinions and pointers are most appreciated.

Thanks

Rob

What dose your buddy dive or will you be solo? Dissimilar tank size between buddies can be a big problem! I like 108s but again it depends on many factors including the type of gas and the type of diving you will be doing! We are similar in size and they work for me caving very well and my buddy uses the same tank and has about the same SAC. The SS back plate maybe too heavy?

 

[TSandM]

There are several issues to consider when contemplating doubles tanks.

One is what you can carry. Most likely that isn't a big issue for you, but even my sturdy buddy who dives the 130s has discovered that, for lesser dives, a set of 72s is awfully nice to walk around in.

A second is what you can trim out. As a taller diver, you aren't going to be happy with doubling up a pair of short tanks. You may not be able to carry enough ballast to offset how head-heavy they are.

The third is how much gas you need for the dives you're contemplating. If you are doing recreational dives on doubles, something like HP100s may be ideal. You can get two good recreational dives off a full set of 100s (or at least most people can). If you are doing a tech dive in the morning, and a recreational dive to follow, you may not have enough gas for both, depending on your consumption.

And finally, if you are diving off boats with compressors, but can't get a good HP fill there, LP tanks may be preferable. They are generally heavier for the same gas volume, but if you can get full 95s, but only 2/3 full 100s, the 95s may end up better for you.

I dive LP85s. I can carry them, they trim out easily for me, I can get them filled (or overfilled) and I can do two good recreational dives with them and still maintain rock bottom for the team. But I'm little, with a very small SAC rate. You have to take your own parameters into consideration.

 

[DA Aquamaster]

I have three sets of X7-100's and have found they work very well for most of my technical diving.

Weight wise a set of X7-100 doubles are very very close to the weight of a set of AL 80's but are 8 lbs more negative - meaning that when I actually dove AL 80 doubles I had to carry an 8 lb v-weight with the AL 80's to be nbeutral with empty tanks in a dry suit and consequently was carrying 8 lbs more total equipment weight with the 80's than with the 100's.

The 80's are now stage bottles and stage bottles are a very convenient answer to more bottom gas on that small percentage of technical dives that I do that could benefit from larger doubles. The idea is to breathe the stage first, breathe it down to bascially nothing (100 psi or so) and keep 1/3rds of the total gas (200 in back gas plus the 80 stage, 280 total) in the back gas tanks as the reserve. In the case of HP 100's with a stage, 2/3rds of 280 is 187 cu ft. or 3200 psi so you turn the dive shortly after switching from the stage to the backgas and you plan to be on the first deco gas by the time you reach 1600 psi to ensure you still have a full 1/3rd reserve.

For cave diving I like LP 95's as well and will probably sell off one set of X7-100's to pay for another set of LP 95's. With a North Flordia cave fill to 3600 psi they are really 130's, while the same 3600 to 3800 psi I normally get in a set of X7-100's is only 105-110 cu ft. and stages in caves are used differently than they are offshore.

That said, the X7 100's are about 20 lbs lighter and they remain my favorite for offshore boat diving where you have to carry them back up the ladder in potentially heavy seas. The AL 80 stage, if taken, can be handed up separately.

A set of 100's or LP 95's are also more than enough for the average 80-130 ft two tank recreational boat dive trip as well.

As Lynn points out double 72's are great for shallower dives where 130 cu ft total is more than enough gas. They are light, trim pretty well and one of my two sets of double 72's are often my choice for air dives in a quarry etc.

 

[Vita.Vivente]

I dive twin steel 120's. As Nereas correctly observed when referring to 130's, these are only for boat dives. I tried a beach dive w/ them, but only once!

 

[jawmendr]

For open water shallow diving, What do any of you think about twin steel 65's. The buoyancy characteristics are comparable to Worthington 100's. They are 16lbs lighter dry weight. I enjoy the twin configuration, redundancy etc. I am concerned about trim?? I dive dry and use a backplate and IQ pak. Is there a distinct disadvantage to such short tanks?

 

[DA Aquamaster]

Short tanks can be hard to trim for some people and it is aggravated by the lack of room on the tanks to move the bands up or down much. Given that a HP 65 is 8 inches shorter than an already short E7-100, I am wondering if bands with a normal 11" between centers spacing will even work.

I do use double steel 72's that offers similar capacity (65 cu ft at 2250 psi) and they work great for both shallower deco dives or for longer recreational dives. Doubled with bands, manifold and emnpty they only weight 67 lbs (75 lbs when full) so they would not be much heavier than double PST 65's - maybe 5-6 lbs total for a set of two. Steel 72's are cheap and still pretty commonly found and being about an inch shorter than an AL 80, they trim pretty well.

So with similar capacity similar weight, a lot less cost, and no overly short trim or band issues, I'd go that route instead.