On 5/27/97 3:09 AM David Grahame Drew wrote:

>Hello,,
>  I'm interested in using twin tanks for deep air diving. I've got some
>general questions and I was wondering if someone here might be able to
>answer them.

Deep air is great. Why, I feel like a million dollars at about 160'. When 
I he 180', woowoo, easy rider, here I come! And take a technical nitrox 
course too, the extra oxygen adds a real nice edge to the narcosis. Kinda 
like a speedball, but underwater.

>1. BCD.
>  Is the lift provided by standard BCD's enough for a twin tank setup? I
>know that most BCD's aren't designed to hold twins, but a friend said he can
>set mine up to hold twins easily, and has done it to his identical BCD a
>long time ago. What sort of lift is needed / desired? My current BCD is a
>Seaquest, with 26 pounds lift.
>

Easy, just use 2 bcds. Get a small then a large, or a large and an extra 
large and wear one on top of the other. According to the great technical 
manufacturing company OMS, you need AT LEAST 100lbs of lift to get you 
off the bottom. The dual BCDs are for redundancy. I mean, what if your 
pull-deflator on your fill hose jams open?

>2. Tanks.
>  What sort of tank setup works best for twins? Do you use twin steel, twin
>Al, or one of each? If using a regular BCD, what would be the best choice?
>Do the tanks need to be / preferred to be, same size / volume / working
>pressure?

As you never know what shape a particular tank is in, I recommend taking 
a LP steel, a HP steel, an Aluminium and a plastic tank and configure 
them in independent quadruples. I saw a show on cable where you auzzies 
were doing some cave exploration, and it looks like independent 
quadruples is standard fare down-under.

>Here's also some personal info, if it helps in answering any of the
>questions. My standard setup is the Seaquest BCD with a steel low-pressure
>100cf tank. My normal wetsuit is a 5mm 'farmer john' with a 5mm jacket. I'm
>5' 10" and weigh 70 kgs. As a result of all the above, I don't need a weight
>belt at all.

Wrongo, mate! You must have enough lead to "plant" yourself on the bottom 
in case a strong current come up! Thats why the 100lbs of lift mentioned 
above.

>I know that tanking a tech course that deals with these questions would be a
>good idea. I intend to take one as soon as the weather around here warms up
>a bit, but any help you could give me now would be appreciated.

Good luck and happy diving!

>
>Thanks in advance,
>David Drew.
>
>dgd02@uo*.ed*.au*
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