Hi Lee!!!

Lee Bell wrote:
>
> Carl and anyone else who would like to respond,

Gee, it seems like you KNEW I'd respond :^)  Of course, I'm always happy
to help you...

> I've been thinking of adding doubles to my diving equipment.  I'm a long way
> from actually doing it, but it's never to early to gather information.  The
> point of doubles, for me, is to allow more bottom time while ensuring
> adequate decompression time.  I do not, at present, plan on multigas diving.

Ok.  It might not be a bad idea to bring along a pony of Pure O2 as
well.  Don't do any of the bullshit gas like 80% which is what a lot of
the strokes mix up.  They do that because they can only get O2 at
2200 psi but their ponies are Al 3000 psi tanks so they top off with
air.  A 30 cu ft pony of O2 could be slung as a stage bottle and carried
on your left side clipped off at your left hip and left shoulder D ring.
You won't even notice it's there if it's rigged properly.

> Since I'm partial to my compact 80's, which are neutral when empty, have a
> service pressure of 3,300 psi and hold the same 78 cubic feet of gas (more
> or less) as standard 80's, these are what I would most likely use.  Since

Not *optimal* but not horrendous either :^)

> they are neutral when empty, but considerably more negative than a single
> compact 80, I presume I need more lift than my 18 lb travel wing.  Since
> this setup would be considerably less negative than steel tanks (I think), I
> assume, but don't know, that the smallest of the Halcyon wings designed for
> doubles would do fine.  To put together such a setup, I presume I will need
> stainless tank bands and some form of manafold.

It's pretty easy to do the math.  We know that a single AL 80 is
centered
around neutrality.  What that means is when full it's roughly 3 lbs
negative
and when empty roughly 3 pounds positive.  That's why it makes such a
good
stage tank.  If your tanks are roughly neutral when empty that means
that
they're roughly 6 lbs neg when full.  12 lbs for both plus a couple more
for the manifold.  Assume that's 15 lbs negative.

But, there's more than meets the eye here.  It's not just how much lift
you
have, it's the design of the wings themselves.  Small wings designed for
single tanks will be narrower.  When inflated they tend to press between
you and the doubles more.  Larger wings (not saying anything about
lift here!!!) have more webbing in the middle so the "wings" can get
more
"outside" (not the best term but I think people will understand) the
tanks.

It sounds like the 38 lb Halcyon wings will be perfect for you!

> Here are my questions:
> 1. Have I assumed anything I should not have in the above information.

Doesn't sound like it.

> 2. Is there a safe way to manifold tanks with Catalina valves or do I have
> to replace the valves with something designed to be manifolded?

Replace them.  Halcyon has their own manifold.  Dive Rite Manifold isn't
bad, Sea Elite either.  Just make sure to replace the plastic knobs with
rubber ones - those plastic ones WILL shatter with a very minimal impact
on anything.  You will also need tank bands.  While there is some
controversy
over which bands are better I don't think the difference in quality here
is nearly as big as many of the other items.  You're smart enough to
pick up a good set of bands.  When in doubt, simply go to a manufacturer
that you trust (Halcyon).

> 3. What are the problems with banding two tanks together, using a separate
> regulator for each tank (not manifolded together)?

There's going to be a big debate on this one.  First, you do not have
access to all your gas all the time.  What this means is that task
loading
on the dive has gone up.  You will have to switch regs on a regular
basis
(no pun intended).  Why?  Well, you want to keep the gas balanced
between
them.  The typical tank switching for independant doubles is to breathe
1/3rd of one tank, 2/3ds of the other, then 1/3 of the last one, at
which
point you should be back on board if you're diving the rule of thirds.

One of the *BIGGEST* problems with doing this, and this is IMPORTANT!!!
is
that you are no longer always breathing from your long hose!!!  One of
the
cornerstones of the Hogarthian setup (which formed the basis of DIR
diving)
is breathing the long hose.  Since this is a setup that you might be
using a lot and not just something you're going to be dealing with
occasionally or on vacation (that type of thing) I think manifolding
the tanks is the proper method.

> 4. Since I do not plan on diving any deeper than I do with a single, is
> there a problem with using a single regulator, fed off a central post on the
> manifold and using the valves on the individual tanks to isolate the gas in
> one bottle from the gas in the other?

I do not believe manifold like this are even made.  I do remember seeing
one that had a reg hookup in the middle but I don't think that it
operated
like you're assuming here.  Anyhow, once again, the problem with using
a single reg is that you now have no secondary reg from which to breathe
when someone take the long hose reg from your mouth.

5' is fine for ocean if you don't have a hip mounted canister light,
If you're a large (tall/whatever) 6' might be better, 7' is you dive
cave and just prefer to keep the *exact* same gear (remember - if you
dive the SAME rig day in and out you will be more fluent with procedures
rather than switching all the time!!!).

> 5. In this configuration, would I normally dive with one tank on and the
> other off or with both on?

Don't know, I'm not going to "go there" since I wouldnt' suggest using
that kind of rig at all.

> 6. What else am I missing.

Don't know - enough money to buy the stuff perhaps :^)

Will you be diving with a wetsuit?  If so, it's a good idea to make sure
you
have SOME type of redundant bouyancy and NO I don't mean those double
bladder wings that belong in some BDSM shop!!!  Take a lift bag or
something
along those lines.  You're *never* going to be THAT negative that you
shouldn't
be able to swim UP against a total loss of bouyancy - it's NOT like
you're
in a cave with dual LP steels, stages, O2 bottle (I know, you typically
drop
this at the beginning of the dive but you don't want to be pinned to the
bottom before you drop it either!).

> I know this is a rather large question, but the list is slow, I'm curious,
> and it's time to learn.  Respond if/when you have time and the inclination.

Good set of questions.  I hope this will lead to some good discussion.
I really just threw this answer together.  Have I missed anything -
don't know,
I have to get moving, I'll probably reread it later and add more.  If
anyone
else sees something that I missed - jump in!

Carl