Bottle Choices for Tech

[Micheal]

@Micheal HP80's are far too negative when empty so they will throw your trim off in the roll direction and because they're so heavy would also have to be compensated into your lift requirements more significantly as well as weighting. HP80's are about 3lbs negative when empty vs an AL80 at +4.4, so that is almost an 8lb buoyancy shift when empty and every 80 would be a 10+lb brick strapped to your side. You couldn't compensate for that with just your body. I can see the appeal if you are short, but unfortunately you need stage/deco bottles to be as close to neutral as possible when full for them to behave and HP80's are about the most negative tanks you can buy today.

I first thought this post was about using HP80s as backmount doubles. But for deco/stage bottles? Bad idea. Stick with AL80/AL40.

Get some HP80s for the shorter people in your life. They’re fab as single tanks for shorter people. Just don’t expect to use them as deco/stage bottles.

I can tell you they’re OK for SM. Not the best. My LP85s and 50s trim out much better.

Thank you for the Sold Answers. I have never purchased an AL80, guess it time to break that trend.

 

[J-Vo]

HP80s are total garbage for any application outside of a handful of very specific uses (backmount tanks for very short/buoyant people). For deco bottles, it's all about the AL80s and 40s until you get to really long O2 stops. That's when LP95s and 108s become useful. But that's a pretty niche application. HP80s will never be ideal for that kind of stuff.

Thinking I would rather have two 80s. If I need that much O2 the redundancy would bring me piece of mind.

 

[tmassey]

Thinking I would rather have two 80s. If I need that much O2 the redundancy would bring me piece of mind.

You've triggered my pedantic side...

If you need gas from both bottles (i.e. a single bottle's volume is insufficient), you do *not* have redundancy -- you have an *increase* in failure points. By spreading your necessary gas volume across two bottles, if you have failures on *either* you are now left with insufficient gas. Sure, you still have a bunch left, but if that amount is not enough, then it's still an emergency.

They only way you have redundancy is if you have N+1 bottles: either two bottles that each have enough, or three or more where you can lose one and still have enough volume. (If you're familiar, think RAID-0 versus RAID-1 versus RAID-5).

 

[J-Vo]

You've triggered my pedantic side...

If you need gas from both bottles (i.e. a single bottle's volume is insufficient), you do *not* have redundancy -- you have an *increase* in failure points. By spreading your necessary gas volume across two bottles, if you have failures on *either* you are now left with insufficient gas. Sure, you still have a bunch left, but if that amount is not enough, then it's still an emergency.

They only way you have redundancy is if you have N+1 bottles: either two bottles that each have enough, or three or more where you can lose one and still have enough volume. (If you're familiar, think RAID-0 versus RAID-1 versus RAID-5).

Agreed. I plan halves for deco gas, so if a needed two then I intend to use only one or less. I haven't actually done a dive like this, but had one planned for my last (canceled) trip.

 

[helodriver87]

Thinking I would rather have two 80s. If I need that much O2 the redundancy would bring me piece of mind.

I'll use AL80s for O2 when I can't maintain sharing reserve in a 40. I suppose you could potentially do an OC dive with enough deco that a step up to a 95 or 108 for O2 would be necessary but I almost always see them used as bailout deco for long rebreather dives. I would never consider an HP80 though. You get the same gas volume and better buoyancy at an easier fill pressure with an AL80.

 

[tbone1004]

the big bottles that @helodriver87 mentioned are really only used in expedition level cave dives. If you believe in carrying 2x deco gas, then you have a 20min deco on AL40, and 40min on AL80. That's quite a bit of O2 stops for most diving. That's almost 90 minutes at 100ft on EAN32 to get 20mins of O2 stops, and almost 2.5hrs to get 40mins of O2 stops and about 40 minutes at 200ft on 18/45 to get 40mins of O2 stops as well. Those are big dives and about the limit of what I'd do in the ocean for total run time.

One thing you haven't really confirmed @Micheal is what your intended dive profiles really look like. How deep for how long?

 

[rjack321]

Thinking I would rather have two 80s. If I need that much O2 the redundancy would bring me piece of mind.

Two 80s in the ocean is a colossal pain in the butt. Especially when you rarely have more than an hour of deco or ~100mins of runtime.

the big bottles that @helodriver87 mentioned are really only used in expedition level cave dives. If you believe in carrying 2x deco gas, then you have a 20min deco on AL40, and 40min on AL80. That's quite a bit of O2 stops for most diving. That's almost 90 minutes at 100ft on EAN32 to get 20mins of O2 stops, and almost 2.5hrs to get 40mins of O2 stops and about 40 minutes at 200ft on 18/45 to get 40mins of O2 stops as well. Those are big dives and about the limit of what I'd do in the ocean for total run time.

One thing you haven't really confirmed @Micheal is what your intended dive profiles really look like. How deep for how long?

An al40 is a 40min bottle? Since when? Most us can do an hour on a 40. There's backgas breaks and there's moving up to 10ft and how bad is the weather going to get while you hang for hours on an 80 with 200% CNS

 

[tbone1004]

@rjack321 if you use 50% of the bottle, you have 20cf available. .65cfm sac @ 1.6ata is close enough to 1cfm.
I don't disagree about backgas breaks and moving to 10ft and I consider mine worth an hour total as well, but for easy math it made sense.
With the profiles I gave, it's about 3 hours total run time which is as long as I ever really want to be under water in the ocean.

 

[ofg-1]

My bottle choice:

 

[RyanT]

My bottle choice:

View attachment 636935

No, that's a terrible choice, Abuelo rum from Panama is far superior!