Advice for a noob

[dscuba]

I'm interested in getting doubles, and a bit confused about what would best suit me. Yes, I'm taking an intro to tec class and have good instructor(s) to ask things like this, but I'm wanting to be extra cautious and get a number of various opinions, so I don't find myself in a situation in a year or two where I wish I'd bought something different.

Do doubles usually employ high pressure or low pressure tanks? Steel or aluminum?

What size tank is usually doubled? (or how to decide what I might want?) I'm a pretty big guy (6'3") so I could probably handle larger tanks if that's preferrable.

How are the doubles usually transported into the shop for a fill?

When diving doubles but diving within no-deco limits do you usually manage to get in 2-3 dives? Or do most have a separate single tank setup for "recreational" diving?

Is some of the additional heft/weight of adding a 2nd tank offset by dropping down the amount of lead one needs to carry? What other issues do I need to consider?

Thanks!

[scottsax]

I don't dive doubles yet, but I'm curious about tank size, too. Doesn't more gas=better? Why choose double LP97s over HP100s or vice versa...? What about double 120s (since I have a collection of them...?)

As far as fills go, I've seen dubs leaned up against a wall to be filled, and I think that's typically how it works. Most times, the backplate and wing are still attached-probably too much of a hassle to disassemble that whole rig.

I know lots of guys that do 2 or 3 rec dives on doubles.

Yes, you'll almost certainly shed weight off your belt, if you even still need one. (Guess it depends how buoyant you and your suit are?)

More info from someone that knows what they're talking about!

[boydski]

Do doubles usually employ high pressure or low pressure tanks? Steel or aluminum?

Most local divers use steel doubles, size depends upon the diver. LP80's/HP100's or LP95's/HP130's are basically the same size and hold the same amount of gas (at the same pressure). Both LP's and HP's are popular.

How are the doubles usually transported into the shop for a fill?

In a truck? Many shops have a hand truck that helps.

When diving doubles but diving within no-deco limits do you usually manage to get in 2-3 dives? Or do most have a separate single tank setup for "recreational" diving?

It is easy to get 2-5 recreational dives out of a set of doubles. Many tech divers also have a separate single tank rig to save the expensive gas in the twins.

Is some of the additional heft/weight of adding a 2nd tank offset by dropping down the amount of lead one needs to carry?

With a steel backplate and a pair of steel tanks, you may not need any additional weight. In other words, you will not need to wear a weight belt. They are really only heavy when you are climbing out of the water with them...

YMMV

[Joshua Smith]

With a steel backplate and a pair of steel tanks, you may not need any additional weight. In other words, you will not need to wear a weight belt. They are really only heavy when you are climbing out of the water with them...

YMMV

One note: I, for one, still needed a weight belt when I dove doubles. My instructor drove home a very important point about dubs to us: It's critical to do a weight check with your dubs down around 500 psi. The "swing" can catch you off guard, otherwise, and it just might be in a decompression scenario. I know a guy who corked from 30', with about a 20 minute decompression obligation; he had never breathed his dubs down that low before, and he became positively buoyant at the end of the dive. (he was fine, but he took a precautionary chamber ride anyway.)

[LCF]

There are a bunch of people on this board with all kinds of double tank setups, and I'm sure you could meet up with a few and try different tanks to see what suits you. Doubles are a lot of mass, and trim out differently for different people, and not always in predictable ways. My husband can just about trim out our 72s and I can't come close, no matter WHAT I do with my weights, but my LP85s trimmed out easily.

What size tanks you need is really determined by the dives you are contemplating. Smaller doubles are fine for the dives in the recreational or 150 foot range, but the gas requirements get iffy if you're looking at Governor-type dives. You could argue that buying the biggest tanks you can haul around would cover you for all contingencies, but I can guarantee you that, if you get into technical diving, you're going to end up with more than one set of doubles anyway. Otherwise, you'll end up with the one set you have filled with entirely the wrong gas for the dives you get the chance to do, and you'll be looking at diving Edmonds on 21/35 :-)

One of the keys to doubles is to try to minimize the amount you have to lift them and put them down. A collapsible hand truck is VERY handy, as is an X-table. Tailgates are wonderful, and you're tall enough to use any sort (I can't get my doubles on the tailgate of my F-250, even if I stand on my toes).

I can easily get two dives off my 85s, even a T1 and a recreational dive -- or three or more recreational dives. A transfill whip is a lovely thing for a doubles owner to have, though, especially if you have any HP tanks at home.

You will take some weight off your belt with doubles, but it's not as much as you think. Assuming you were diving a steel tank to begin with, you're adding the 1 to 2 pounds negative of the second tank, as well as 3 or 4 lbs for the bands and manifold, and a pound or two for the second first stage. I dive 31 lbs of total ballast with a single steel tank, and 22 total pounds with double 85s. I suspect it's very common for people to underestimate the weight they really OUGHT to carry with doubles. My Cave 2 instructor insisted, despite my careful work at home, that I did not need the six pound tail weight I wanted. It worked fine (except for screwing up my trim) because we never breathed the tanks down below about 2000 psi in the whole class. It wouldn't have worked with them empty, though, and I'm glad I didn't have to crawl out on the ceiling to prove it.

[Burntchef]

Is some of the additional heft/weight of adding a 2nd tank offset by dropping down the amount of lead one needs to carry?

Thanks!

with my lp95s or hp119s i use a 10# v weight, and nothing else. for the 119s its a bit much but at the end of a long dive a like a lot of gas in my suit for warmth

[Joshua Smith]

It worked fine (except for screwing up my trim) because we never breathed the tanks down below about 2000 psi in the whole class. It wouldn't have worked with them empty, though, and I'm glad I didn't have to crawl out on the ceiling to prove it.

Not that the rest of Lynne's post wasn't excellent advice, but I just wanted to stress this point. When you start diving doubles, LEARN HOW THE BUOYANCY CHARACTERISTICS CHANGE WHEN YOU GET UNDER 500PSI. Before you find out under unfortunate circumstances.

[kagey747]

How's your air consumption? Doubled HP100's were fine for me down to 150 fsw, but when I started deeper trimix, I had to go to 130's because I suck air/mix like a ... a lot. Started out switching tanks on a single BP?W but quickly tired of that and now have seperate single and doubles setups. Same with the regs, became a pain to keep switching hose/SPG/transmitter configs whenever I changed which tank config I chose to dive. +1 on the folding handcart. ++1 on the pickup tailgate. My 2psi.

[kagey747]

I also found that an 11# v-weight allowed me to remove the additional weights on my rig. 2# ankle weights are all that's needed with the v-weight for me. I use the 100's frequently for rec dives, the 130's only for deep dives where they're required. The v-weight/ankle combo work fine, although it's a bit twitchy at the end of the third rec dive (500psi).

[loanwolf]

It worked fine (except for screwing up my trim) because we never breathed the tanks down below about 2000 psi in the whole class. It wouldn't have worked with them empty, though, and I'm glad I didn't have to crawl out on the ceiling to prove it.

Not that the rest of Lynne's post wasn't excellent advice, but I just wanted to stress this point. When you start diving doubles, LEARN HOW THE BUOYANCY CHARACTERISTICS CHANGE WHEN YOU GET UNDER 500PSI. Before you find out under unfortunate circumstances.

What Josh has put here is very important Mike found this out last weekend when we were practicing his drills. It was the first time he had dove with someone that could stay in the water long enough to suck his twins below 700psi and he went light. I gave him one of my bailout bottles to add a little wight to him. Nothing sucks more than going light at 20' it is stressful and I usually end up getting cramps tying to fight to keep myself down when I goof up.