Northwest Dive Club

Hello there
I would say I am still fairly new to diving in general but working on completing my kit out knowing that I will be focusing on doing tech, wreck diving soon. I would say 90% of tech divers go with steel doubles over aluminum but what about the 30 and 40 Deco bottles? Taking costs out of the equation is there a standard for material? I see so few steel I know the cost may play a big part but from the specs I have seen on a steel 40 seem to show negative to neutral boyancy when empty VS + a few lbs on the alu...

Thanks
Dave

I only know a few folks that use steels for stages over AL. I understand its perhaps more common in cavers. I don't recall the rationale.

Steel tanks are gonna hang, AL will float abit. For my trimix bottles, I actually hang a few pounds on the end to drop the ass down into trim. Also how they hang while being drawn down is different between steels and AL.

If you are serious about eventually moving to tech, don't even consider 30's, they aren't enough.

I've recently come to appreciate the characteristics of the Alu72 tanks for deco bottles. They sling easier than the 80s and are nicer to carry on land as well. I have an Alu40 set up for O2, but haven't used it yet.

1) the deco bottle will never be emptied on a normal dive
2) aluminum 40 is pretty close to neutral when empty if it has a reg on it
3) if you buddy has a deco bottle failure are you prepared to try to hand him a brick to use some of your deco gas? And get that brick back when its your turn again? If you drop it, how are you planning on staying down since the steel was part of your weighting? If you carry enough lead to stay down without that steel bottle you'll be quite overweighted.

Pretty much everybody uses AL40s as their entry level deco bottle for these reasons.

Steel deco bottles are commonly used in cave diving since you are dropping the bottle on the way in at 20ft and want it to stay put there. And on return you're just plastering yourself to the ceiling like a Michelin man while you're on 100% @ 20ft

What Richard said ^^^

I"ll add that an AL30 is common for O2 deco bottles for around the 180-220ft range, depending on bottom time. But if you dont have any yet, I'd recommend buying into AL40's when you can get then for a good deal.. They will work perfect for a 200ft for 30min type dive.

You may later want some AL80 for 50% deco gas for bigger dives, but thats mostly again on the 200ft and deeper range.

+1 on AL30s as O2 bottles. Not every dive is a "serious" deco dive. We do the Diamond Knot on 25/25 with ~30mins BT @ 105-110ft and 5 to 10mins of deco on 100%. Al30s are super compact without all the drag of a bigger bottle in the current. Its more than enough deco gas for this kind of dive.

Al40s are more versatile but 30s are nice and tidy in the right circumstances. 30s are slightly negative in saltwater with a reg on.

ALi 30s and 40s are both negative in freshwater with regs on them. Even 80s are just barely positive depending on the reg. I can't imagine doing the PB4Y with a steel deco bottle, or one of the minesweepers (200ft, 2 deco gases). Steel would be like giant bricks in freshwater, full with regs on them.