Sizing Tank Height for Sidemount

[MrBlenny]

@MrBlenny the buoyancy swing is a function of gas volume and has nothing to do with the tank. I.e. 80cf of air has a mass of 6.4lbs, so from full to empty with a pair of them there is a swing of 12.8lbs. That holds true for any other tank that holds 80cf, whether it is an overfilled LP50, or an underfilled LP121. 80cf of air has a swing of 12.8lbs regardless of what it is put in.
Now, an AL80 becomes positively buoyant when empty, but you have to factor that in regardless. With the AL80 you will have more lead on your rig than you would with a steel tank, but the buoyancy shift is a function of gas volume consumed.

I will emphasize that if I could do the dives that I'm doing on AL80's practically, then I would in a heart beat as they make sidemount so easy. All of those videos that you see of bottle handling on youtube are done with AL80's for a reason.....

Thanks, I was thinking of the extra lead that AL require the diver to wear, as opposed to Steel, but didn't properly say so. Nonetheless, given how pro-steel most cold water divers are, it's interesting to hear a sound argument for AL.

 

[tbone1004]

@MrBlenny in backmount it's a different discussion. In both situations it increases total rig weight, so the AL80 is less efficient in total rig weight:gas volume carried, but with sidemount you don't have the bottles on you, so it's less critical there

 

[MrBlenny]

Given what I've learned so far, it sounds like I should contain my enthusiasm and hold off from buying anything right now, get through training, pick up some AL80's, and rent a bunch of different steels from the shop before committing to anything...i.e. I just reaffirmed I lack the necessary experience to make an intelligent decision

 

[rjack321]

If you are doing deco in al80s the most deco gas you'll ever plausibly need is an al40. al30s are cute and work well as O2 bottles

 

[tbone1004]

@rjack321 I actually don't like AL30's at all. They're too heavy in the water, AL40's all the way!

 

[MrBlenny]

If you are doing deco in al80s the most deco gas you'll ever plausibly need is an al40. al30s are cute and work well as O2 bottles

Actually have an AL40 as a pony already! Since I'm presently diving a single tank, I like knowing I can take my time in the event of a serious gas failure.