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Mtrewyn
12-15-2007, 00:36
Just wondering Why would you need or want to use double tanks?

I mean other than for planed deco stops can you really use more air than your bottom time allows for?

I'm new and forgive me for sounding dumb, but I was think about this today while I was at work and it was really bothering me.:smiley5:

texdiveguy
12-15-2007, 00:56
In a 'nut shell'........
There are many reasons for diving doubles in technical diving. :)
Within the recreation level of diving it is not real common, but there are exception were a diver might opt to use doubles as a form of a redundant gas delivery system,,or another common use is that you don't have to swap out cylinders between dives,,and in some cases extended range mid depth nitrox diving.

in_cavediver
12-15-2007, 15:50
Just wondering Why would you need or want to use double tanks?

I mean other than for planed deco stops can you really use more air than your bottom time allows for?

I'm new and forgive me for sounding dumb, but I was think about this today while I was at work and it was really bothering me.:smiley5:

Doubles does not mean excessive gas. While I have many large sets, I have played with a set of 45's which for lightweight rec diving profiles, would be great. They are short, compact, negative, lightweight and redundant but yield only 90cft. They are also more stable than a single in my opinion.

If you want to know why doubles for most cases though, its redundant gas and a lot of it. Usually these dives aren't limited by NDL's but rather planned bottom times. (what's a little deco amount friends). For instance my 104's cave filled are 250-275cft of gas. When diving thirds, I can get one way travel on 80+cft. That translates to bottom times of 90-150 minutes when swimming at 50-60'.

Dive-aholic
12-15-2007, 18:56
I've done 2 hour long dives in doubles without ever getting a deco obligation. It all depends on the depth. Of course, those dives were in caves, but there was no deco obligation. :D The thing about cave diving is you use 1/3 of your air supply for penetration, 1/3 for exit, and 1/3 for emergencies. So it's not uncommon to exit a cave with 1200-1800 psi left in your tanks (depending on the amount of flow in the cave).

Mtrewyn
12-15-2007, 19:10
The stability issue makes alot of sense, like I said I was just wondering, It is a wonder I get anything done at work, ADD sucks, and my mind wonders alot.

thanks for the info.!

navyhmc
12-16-2007, 01:26
Outside the technical areas, as noted: A long shallow dive NDL for 40' is 140 minutes-out of single 80 reach unless your SAC is around .20. Stability is also a reason. I used to dive with a guy that carried double 50's when the rest of us had 80's just because he felt it balanced him better. One guy I dove with once or twice used twin 80's because he thought it made him look like a diver (he was worried about his hair 5 minutes after a dive too.)

WD8CDH
12-18-2007, 13:33
I almost always dive small doubles or triples. For me, the balance and profile is better. My primary rig is 3 - 40's My secondary rig is double or triple 35's.

DivingCRNA
12-18-2007, 17:29
Chicks think they make you look hot!

LOL

Iceman
12-18-2007, 17:38
See the Redundant Breathing System thread.

MSilvia
12-19-2007, 08:16
You can get a lot more diving in at shallow depths before having to surface, the redundancy is great on deeper/penetration dives whether you use all the gas in a single dive or not, and if you do deco dives where you don't have an NDL constraint, it's a no-brainer.

Dark Wolf
12-23-2007, 09:58
Chicks think they make you look hot!

LOL


REALLY!?! Boy, I must be doing something else wrong then:smiley5:!


DW

kancho
01-03-2008, 07:30
These smaller tanks are the al or steel.. I am wondering if it is worth have double 80's Aluminum. Adding 6 lbs of weight is a bit heavy.

fisheater
01-03-2008, 09:04
Hey. Mike Nelson used doubles. 'Nuff said.

cummings66
01-03-2008, 11:41
Who's Mike Nelson?

in_cavediver
01-03-2008, 11:42
Who's Mike Nelson?

Wasn't he in Sea Hunt (lloyd bridges)?????

ianr33
01-03-2008, 11:44
These smaller tanks are the al or steel.. I am wondering if it is worth have double 80's Aluminum. Adding 6 lbs of weight is a bit heavy.

Really depends what type of diving you are planning on doing with them. I use Al doubles for all my local dives.They are cheap and MUCH lighter than my set of 104's.

With the Al 80's and a drysuit I use a steel plate,a 6 lb V weight and a 4 lb weight on my waistbelt. Summer diving in a 3 mm wetsuit all I need is the backplate (although I add a 2 lb weight to my waistbelt for trim)

For a drysuit or a thick wetsuit you are going to need weight somewhere.Either in the tanks (steel) or a V weight does not make much difference to me (anywhere but on a weightbelt !! )

ianr33
01-03-2008, 11:47
Who's Mike Nelson?

Wasn't he in Sea Hunt (lloyd bridges)?????

I dont know as I am far too young to remember anything that far back.

Good that we have some old timers on this board to answer Ancient History questions :smiley36:

CompuDude
01-03-2008, 13:02
These smaller tanks are the al or steel.. I am wondering if it is worth have double 80's Aluminum. Adding 6 lbs of weight is a bit heavy.

I'm not a fan for cold water diving, since as you noticed, you have to add quite a bit of lead to counteract the positive buoyancy (+4 x2 = 8lbs), but for warmer waters they are quite popular. Double Al.80's are used regularly for cenote diving in Mexico.

in_cavediver
01-03-2008, 17:06
Who's Mike Nelson?

Wasn't he in Sea Hunt (lloyd bridges)?????

I dont know as I am far too young to remember anything that far back.

Good that we have some old timers on this board to answer Ancient History questions :smiley36:

I'm not THAT old - I'm still in my 30's for heavens sake.....

Puffer Fish
01-03-2008, 17:42
Who's Mike Nelson?

Wasn't he in Sea Hunt (lloyd bridges)?????

I dont know as I am far too young to remember anything that far back.

Good that we have some old timers on this board to answer Ancient History questions :smiley36:

I'm not THAT old - I'm still in my 30's for heavens sake.....
Barely out of diapers actually. Wonder how many dive knifes he sold?

Actually, unless you are doing some sort of specialty diving, I don't see the reason to use them...even though I used a pair for over 20 years. However, if I were going to get another set, it would only be in HP steel. Worthington 100's, for example... weigh 33 lbs, and are 2.5 lbs negative when empty. Your standard al 80 (which is not 80 cubic ft), is 31.4 lbs and 4.4 positive. As doubles, to be zero with each system, with an empty tank (ok, that is not really necessary... but it looks better)...you have 33 lbs of tanks, and 5 lbs of negative weight. For the Aluminum to be at the same level, they would be 62.8 + 13.8, or 76.6 lbs.. or 10 lbs more and you only get 77.4 x 2 or 154.8 cubic ft of gas versus 200.

Ok, there is a giant cost difference, but hey, it's a hobby...

fisheater
01-03-2008, 23:25
Who's Mike Nelson?

Wasn't he in Sea Hunt (lloyd bridges)?????

Kids these days! :smiley36:

He sold America on diving. For you young 'ens who've never seen Sea Hunt, the reason why there are LDSs around is because the generation before you wanted to Be Like Mike.

texdiveguy
01-03-2008, 23:37
Sea Hunt...what are great show....have all the series in a DVD collection!

kancho
01-04-2008, 07:52
Thanks for the info guys.. If I find a good deal on another AL maybe I will get it. I was reading in another post any AL tank manufactured prior to 1990 isn't worth buying right?

mwhities
01-04-2008, 08:17
I'm going to eventually get to doubles for cavern/cave diving. Otherwise, shallow extended BT wreck dives (shallow as in less than 130fsw, greater than 75fsw.).

ianr33
01-04-2008, 09:34
Thanks for the info guys.. If I find a good deal on another AL maybe I will get it. I was reading in another post any AL tank manufactured prior to 1990 isn't worth buying right?

I dont think its worth buying used Al tanks. A new one delivered to your door from Scubatoys is only $160-$170. If using it for doubles you can sell the valve to save a few $$. No messing with VIPs/Hydros and no chance of it only being useful for a windchime.

Old Al tanks are not worth the hassle to save a few $$.