Why use aluminum doubles for ocean diving???

[JT2]

I understand why one should use aluminum doubles instead of steel doubles when diving in a wetsuit, but I have heard from several people that even if they are diving a drysuit they will still wear Aluminum doubles instead of steel if they are in the ocean. I don't understand this method of thinking, is this taught in the GUE classes as well as most other tech agencies or have I just gotten bad information? I am hoping to take my DIRF class through Mike Ferrara's shop if I can make the dates work and I am sure I can get most of my questions answered there, I was just curious what the thinking on this subject was.
Thanks!

 

[cadet diver]

I have dove Al doubles with a drysuit before and dont recomend it to anyone because you are just too bouyant. It requires a ton of weight to balance out. I can't speak for GUE but TDI and Naui leave it up to the diver to decide.

 

[lucid]

I dive Double Aluminum 80's with a Drysuit. I have a 8 pound v-weight on my tanks and wear less weight in my belt than most do when diving a wetsuit.

 

[ericfine50]

It all is about diving a balanced rig. One that will allow you to swim it up after ditching weight. If you are to heavy and have a wing failuar or DS failuar, you may not be able to get up the anchor line/back to the boat.

Eric:wacko:

 

[LUBOLD8431]

Some people are comfortable diving al80's doubles. SOme people are not. Its a personal choice. You have to figure out whats going to be the best and most comfortable for you. Do you need alot of weight to get down with a drysuit and a steel 100 or 120??? If you do, then you should probably dive a set of steel doubles. The thing that alot of people are worried about on this board is to be able to swim a heavy set of doubles up from the bottom if you lose your buoyancy system. First of all, thats asking for alot of things to go wrong. I always dive with a backup system of some type, and usually two (one being a lift bag, and YES, you can if you NEED to, use it as a buoyancy device.) I bet GUE doesnt teach you that though... I have never had a problem with my big low pressure steels, but then again, I am a bigger guy, and I can handle them. You have to find a set of doubles that works for you, as far as the size goes, and how much gas you will need for the dives you plan on doing... See if you can rent some before buying... That always helps in making a decision.

 

[O-ring]

I have a set of AL80 doubles and have used them for ocean diving in the past. However, I am curious to see how this pans out because as we start to push deeper we are realizing that you cannot dive thirds with AL80 doubles unless you start carrying stages. I seem to remember a piece by George saying that AL80 doubles and AL stages were the preferred ocean diving system, but I am beginning to wonder since most of these long exposure dives are being conducted in a drysuit.

As I understand it, part of the reasoning was to keep the bottom times short since ocean conditions are rapidly changing. However, for example, if you are diving to 170 with a .75 SAC for 30 minutes you cannot do the dive on AL80 doubles without stages. Would this system still be preferable here even in a drysuit? Seems easier to me to strap on the 104s...

 

[Rick Murchison]

I dive steels with a drysuit and aluminum with a wetsuit regardless whether it's in the ocean or not.
In the ocean I always carry a lift bag so I can "ride" to the surface if necessary no matter what happens to my other buoyancy devices.
Rick

 

[AzAtty]

From GI3's equipment list:

AL 80'S FOR OCEAN WITH WETSUIT. (sic)

However, in his "Doing it Right Gear Configuration" article, GI3 says that AL 80's are the cylinder of choice for ocean diving, but that steel cylinders must be used with a drysuit in caves. The rationale he gives for these configurations is buoyancy. He says that in the ocean, you want to be only "reasonably negative" when full and neutral when empty, and swimmable once you ditch ballast. But in a cave, he says, you want to be "negative enough" to stay off the ceiling when low on gas. The actual article isn't clear on whether the use of a drysuit in the ocean changes his cylinder recommendation. Or maybe his statement is clear--only use AL 80's in the ocean regardless of your exposure suit--and I'm just trying to avoid building an aluminum doubles rig.

If buoyancy is the only issue, it seems that you'd be able to work around the negative buoyancy of double steels with a dry suit, substitution of an aluminum plate, or removing weight from the weightbelt/channel weights/whatever.

If limiting immersion time in the ocean is the issue (GUE < 90 min.), chopping your back gas by a third seems like a bit of a crutch to prevent people from staying down too long. Somehow, I don't think GI3 would rely upon running out of gas as a method of limiting exposure time--"If you fat strokes are too stupid to watch your bottom timer you're all gonna DIE!".

Oh, and on the topic of backup buoyancy, I seem to recall that JJ's book mentions the use of a lift bag or SMB as a source of redundant buoyancy. And since learning how to deploy a SMB/lift bag is part of the GUE DIR-F course, I think that most students will get the picture that unless you actively try to keep yourself down, the SMB/lift bag can provide you with plenty of buoyancy in an emergency.

 

[MechDiver]

O-ring once bubbled...

I seem to remember a piece by George saying that AL80 doubles and AL stages were the preferred ocean diving system, but I am beginning to wonder since most of these long exposure dives are being conducted in a drysuit.

I dive what I choose, where I choose. I don't need permission from George.

MD

 

[O-ring]

MechDiver once bubbled...


I dive what I choose, where I choose. I don't need permission from George.

MD

Nobody needs permission from George...but I do remember he made a case somewhere for AL doubles in the ocean.

I felt it was relevant to the discussion..