How would my air consumption change on double 50s vs 85s?

[yle]

Here are some numbers from a recent dive:

Duration: 29 minutes
Average Depth: 34 ft
Starting PSI: 2960
Ending PSI: 2058
Calculated SAC: 16 (ROUNDUP(((2960-2058)/29)/(34/33+1)))

Should be

(2960-2058) psi
------------------------------------------------------------ = 0.94 cu ft / min
[16.3 psi / cu ft] [29 min] (34/33 + 1)

 

[seeker242]

A shop guy told me yesterday I would be shocked by how much my air consumption would decrease

AKA, shop guy is giving you a sales pitch to try and convince you to purchase more gear from him. In other words, shop guy is full of it.

 

[CaveSloth]

So is my math right or wrong?

 

[tursiops]

So is my math right or wrong?

Your math is right. Mea culpa, Here is my note I added back on my post where I questioned it:

ADDED: And that's the problem with SAC; I did not take into account he was diving double LP85s and had wrongly assumed a single AL80. His RMV based on 15.7 psi/min for his tanks would be 0.96 cuft/min.​

I apologize for misleading you, but you should work on that awful SAC/RMV!

 

[CaveSloth]

I think maybe I just open up the knobs on the regulator all the way and probably don't need to.

Also I need to lose 60 lbs.

 

[kensuf]

I wouldn't recommend it unless your plan is to stay in shallow caves (pretty much Telford and maybe parts of Peacock) or very close to the entrance. Lp50s simply don't have the volume of gas needed when you're at 4ATA and 1000' back to allow for problem solving in a tight pickle.

 

[grantctobin]

I think maybe I just open up the knobs on the regulator all the way and probably don't need to.

Also I need to lose 60 lbs.

Increasing breathing resistance is more likely to give you a CO2 headache that it is to markedly improve your sac. I'd advise against tightening the resistance knob.

 

[tursiops]

Increasing breathing resistance is more likely to give you a CO2 headache that it is to markedly improve your sac. I'd advise against tightening the resistance knob.

Depends on whether it is freeflowing and bubbling away from his mouth, or just easy to breathe.

 

[UCFKnightDiver]

I think maybe I just open up the knobs on the regulator all the way and probably don't need to.

Also I need to lose 60 lbs.

Increasing work of breathing by detuning your reg via the adjustment knob seems like a not so great idea and is likely to lead to more stress, higher CO2 retention, and potentially more gas used due to the previous two points.

 

[Doppler]

Dive shop guy sounds like a real clown. No way anyone will get any significant improvement with such an insignificant change in surface area. Conditioning and other anatomical factors will play a much bigger role.

What he said. I was gonna ask you who is "shop guy." Because working in a shop does not qualify anyone to make blanket statements based on dodgy data and push it as fact or advice.

Certainly, mass has inertia and moving inertia in water takes work... more mass = more work and **** streamlining... we're talking scuba cylinders... on the whole, those puppies are reasonably streamlined at swimming speeds.

Do your own research but if not, apply simple logic... here's an exercise for you. What's the mass of one set of tanks as a ratio to the other set of tanks? Now, what's the ratio of the # of litres (cubic feet if you're dealing with American conventional/customary units) in one set of tanks compared to the other set. Write those numbers down on a big piece of paper and stare at them for a while.

That should give you an answer. Not perfect but close enough to start doing primary research yourself.