When to Double?

[Green_Manelishi]

due to the dives involved in the class, something like
"Technical EANx" or "Extended Range" will 'teach' you to
use doubles. WITH THAT SAID, I concur with the comment they
ae best used FIRST TIME in a pool or other controlled
environment so you become somewhat familiar with the weight, etc.

I was once on a dive boat and overheard one
of the "divers" (and I use that term loosely) state
"this is my first time with doubles and my new BC". he
had heavy STEEL doubles with a wetsuit and was
about to step into 100 feet of cold, dark New England
water.

 

[Frog]

Interesting and helpful thread by the way.

I will be buying some doubles soon and wondered what was the popular opinion on when to use Steel or Aluminium doubles. Everyone i have dived with so far who have used doubles, have used steel faber lightweights. Do divers uing aluminium choose to do so because they are lighter to carry on land?

 

[Rick Murchison]

There are several interesting points in this thread..
(1) Do doubles require special training? Depends - if you double up Aluminum 80's and dive in open water, probably not. On the other hand, if you double up Steel 104's and want to dive in a "technical" environment, then there are gas management and buoyancy considerations related to doubles that can be life-threatening without training on the use and the effect of the doubles.
Diving big steel doubles even in the most benign environment introduces buoyancy considerations that must be carefully considered.
(2) Tank sizes - Litres vs Cubic Feet - sort of an apples and oranges comparison. The Litre rating system is a measurement of the interior volume of the tank, while the cubic foot rating is expressing how much gas (measured at 1 ATM) can be shoved into the tank at it's working pressure (approximately). So, for example, if a LP 11L tank is a "72" at 2475 psi, a "standard" 11L tank rated for 3000 psi would now be an "85" and a HP 11L tank rated at 3500 psi would be a "100."
In other words, the "conversion formula" must include the working pressure to do its job.
(3) As far as I know, there's no "doubles" course - but training in their use is included in almost any technical course.
Rick

 

[large_diver]

Disclaimer -- I don't dive doubles

Some of the steel vs alum decision is related to the type of exposure protection you're using. If diving a wet suit, diving big steel doubles is risky -- as your wet suit compresses at deeper depths, you may have some significant trouble swimming to the surface in the event of an emergency (BC failure, air not turned on at surface etc.)

If wearing a trilam-type dry suit, steels obviously let you get weight off of your belt, as they are more negatively buoyant

Not a complete discussion -- just s few key nuggets

 

[The Chairman]

Originally posted by Frog
I will be buying some doubles soon and wondered what was the popular opinion on when to use Steel or Aluminium doubles.

Hey Frog and all,

Boy another can of worms... but which metal do we make the can out of???

There are many arguments one way or the other... but it boils down to personal preference.

Al... Which is actually lighter than steel, and significantly cheaper. If a "neutral buoyancy" tank is not used than you will oodles and oodles of positive buoyancy (can you say "cork"?)at the end of your dive, necessitating lots of lead, thereby offsetting any gain from the lighter tanks.

FE... This is my favorite because of the weighting issue. Yes they are significantly heavier than al alone, but I dive with no weights in fresh and very little in salt. I think my total weight is about five pounds lighter than if I had to use Al with the additional weights. The material is stronger and so HP tanks are easier to make as well.

Now don't confuse doubles with technical diving. You don't have to be a tech diver to enjoy doubles. If you do tech diving get the training for that, but just doubles by themselves do not require a class. That being said, I have found many of the same benefits in just going to a larger steel tank, and using it solo. My Pressed Steel HP120s give me almost as much air as my dual 72s, are just a little longer, and on a dive boat, they fit into the rack just fine. They are a little more "top heavy" but I have adjusted to that as well.

 

[Frog]

All great imput being put into this thread, keep it coming.

The reason i aksed about the conversion between cubic feet and litres is just so i could get an idea of what you guys are using. It seems that you guys who i believe most are from the US are using relatively large tanks compared to openwater divers in the UK. Here in the UK the majority use 10-12 (66-80 cubic feet) litre 232 BAR doubles. Alot of what i have seen on these boards suggests that 104's to 120's (16-19 Litres) are commonplace in the US.

Wonder why theres such a gap between the size of tank being used in the US and the UK? Could it be because most of you in the US are using your tanks for cave diving.

 

[Rick Murchison]

There isn't.
In the United States the typical recreational diver uses an AL 80 almost exclusively. On this board, you see "other than 80" discussed a lot because 80's are so common they aren't worthy of discussion.
Rick

 

[Frog]

Rick yeh i know but i was talking about steel doubles.

 

[TexasMike]

• Originally posted by Green_Manelishi
  
  due to the dives involved in the class, something like
  "Technical EANx" or "Extended Range" will 'teach' you to
  use doubles. WITH THAT SAID, I concur with the comment they
  ae best used FIRST TIME in a pool or other controlled
  environment so you become somewhat familiar with the weight, etc.

Thanks...This answered my question and fits into what I was thinking...especially since I plan to work through the TDI set of courses.

And I totally agree about diving in the pool or shallow environment (such as Athens here in Texas) whenever you do a major gear change. Make sense to work through every scenario in a confined water area before getting in "way over your head" as it were.

I don't plan to dive doubles for a while, but wanted to ask the question since I'll be taking a trip with a very experienced friend who will be using doubles during his dive profiles (I'll be buddied with another single tanker).

 

[Walter]

Frog,

I make most of my dives with twin slim 72's.

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