What size doubles?

[Mr. Bubble]

I am in the market to get a set of twins, but I am not sure what sizt to get. I have seen several set ups. 95, 100,105, 120 and even 130's.

I know the first response will be..."it depends on what you want to do.".....

well, I want to wreck dive and cave dive...mostly within the recreational 130 ft range, but maybe some limited extended range.....

man...those twin 130's were heavy!

So, what do you recommend and why?

Thanks

Mr. B

 

[TSandM]

I recommend a set of tanks that will do what you want, and will balance easily for you.

For example . . . If you want to get two recreational dives out of a set of doubles, you need to sit down and calculate the likely depths and your necessary reserves, and figure out how big a tank you need to be able to do two dives.

If you are going to do one tech dive, you need to figure out your gas requirements and your necessary reserve, and see what size tank will do that for you.

Then, once you have a ballpark of the cubic feet you need, you need to figure out what will balance for you. Tall people often do better with longer tanks. I know I tried to dive doubled LP72s for months, and could never get them to balance well. The very first dive with my LP85s was like coming home

Ideal is to be able to borrow various sorts of tanks and try them, to see what feels right in the water.

 

[xiSkiGuy]

How tall are you? As TS&M alluded to, some people find that certain size tanks work well for them and some don't. I'm 6'2 and I find LP95s and X7-100s to be too short to trim out well. X8-130s work pretty well for me. AL80s and LP85s are the easiest I've tried. I haven't tried X7-80s or LP120s but I imagine they would be too short and too tall respectively. If possible, try some different tanks before you buy.

 

[Rick Inman]

Another thing to toss into the mix, depending of who/where you are getting your fills, it can be more difficult to...ah...maximize your fills in a HP set than a LP set. IOWs, when I show up to the dive site with my LP95's "full", I'll often have more CF of gas than my buddy with his "full" HP 100s (although I love how the 100's ride on me).

 

[Juno]

The "typical" doubles are LP95's/98's. I prefer the Fabers as they are a little lighter, but that size is a good all around tank. As the others have stated, from there you may want larger or smaller depending on your size, location etc. For most folks though, those tanks work out pretty well.

 

[nereas]

I recommend that you do the math first.

I have twin 130s which I use for boat diving, and twin 72s which I use for beach diving.

The 72s are really 65s that fill to 71 with a plus rating, which mine no longer have since they are so old. The 72s are the lightest twin tanks that I could find. However they are hard to find anymore. New 85s are now more common to be used for the lite end of twin tank diving.

The 130s often allow for 2 dives from a boat, although there is little hope of doing any beach diving with them since they are so heavy. But I designed them with the thought of my deepest dive in mind for 20 mins plus the rule of thirds. If you get yourself a copy of V-Planner and type-in all your data including RMV, then it will tell you how much gas you need of each mix on an extreme dive (TMX 10/70, TMX 20/40, TMX 30/30, EAN 50, and 100% O2) for a maximum dive (to 100 meters for 20 mins). This will then tell you how big your biggest tanks ever need to be, after you add on for the rule of thirds.

As far as trim is concerned, with long tanks (anything besides HP 80s) you should be able to move your bands up or down to create perfect trim. The myth that only a certain tank gives you good trim is foolishness.

And if your dive shop does not have a booster pump hooked up, so that it can pump to 3500 psi, then you need to find a new dive shop before you go tech.

If I lived in South Carolina, I would be diving U-Boats as much as possible, and forget about caves. A shipwreck has more sea life upon it than any reef (or cave) would ever have. In that case, your MOD would be your deepest local shipwreck. And the size of your largest doubles then calculated with V-Planner based on that deepest wreck.

V-Planner VPM & VPM-B dive decompression software

 

[Scared Silly]

The 72s are really 65s that fill to 71 with a plus rating, which mine no longer have since they are so old.

There should not be anything from preventing you from having the "+" rating put on the cylinders (other than them failing it but passing hydro).

There is often the myth that the "+" is good for only the first hydro. Or if it is missing on one hydro then it can not be done one the next. You just need to find a tester who is willing to take the time to find the right specs for it.

 

[nereas]

There should not be anything from preventing you from having the "+" rating put on the cylinders (other than them failing it but passing hydro).

There is often the myth that the "+" is good for only the first hydro. Or if it is missing on one hydro then it can not be done one the next. You just need to find a tester who is willing to take the time to find the right specs for it.

Thanks!

 

[xiSkiGuy]

If you get yourself a copy of V-Planner and type-in all your data including RMV, then it will tell you how much gas you need of each mix on an extreme dive (TMX 10/70, TMX 20/40, TMX 30/30, EAN 50, and 100% O2) for a maximum dive (to 100 meters for 20 mins). This will then tell you how big your biggest tanks ever need to be, after you add on for the rule of thirds.

He's looking for his first set of doubles. It's probably better to find a manageable size and reasonable volume, not necessarily the largest tanks he'll ever need.

As far as trim is concerned, with long tanks (anything besides HP 80s) you should be able to move your bands up or down to create perfect trim. The myth that only a certain tank gives you good trim is foolishness.

Again, he's looking for his first set of doubles. A skilled doubles diver can dive any tanks and make it look easy. But picking a tank that is best suited to your individual build will ease the transition. And moving tanks too far in the bands can make valve manipulation difficult.

If I lived in South Carolina, I would be diving U-Boats as much as possible, and forget about caves.

Which U-boats would you be diving off South Carolina?

A shipwreck has more sea life upon it than any reef (or cave) would ever have.

Sealife isn't usually why people dive caves. And from Upstate South Carolina, North Florida cave country is about the same drive as the region's best wreck diving (Morehead City).

 

[texdiveguy]

IMO..... get what 'works' best for your body size and your diving physical conditioning,,,then look at the type of diving you intend to do, this part of the formula will include a 'number' of factors. In the end or down the road you may just end up with several different sets.

Know one can tell you whats best....try out several combo's.....visit with local divers in your area whom are diving doubles and get a feel from them regarding their kits. We all have such differing needs and opinions when it comes to cylinder selection.

Having said that....I persl. prefer a smaller set....I really like the Worthington st. lp85's as a 'general fit' for many of my dive profiles/sites and my physical size and comfort zone of fit....a larger set does at times come into the factoring of certain dives so you must remain flexible and comfortable with change.