LP45/50s in cave diving

[Superlyte27]

My cave/CCR instructor said 50s are too small for even OC intro level cave dives (I asked right before I took my class). For OC SM, I use 85s. It’s too bad as 50s are lovely to dive. I use 50s for CCR dil/BO (Kiss Spirit) on open water dives (mod 1 right now) and I’ll use them for shorter cave dives when I get to that point (not enough hours yet). I do see plenty of people using 50s for CCR BO, especially with Kiss units or Choptima.

I’d probably get another opinion.

 

[Superlyte27]

How far and at what depth do you feel comfortable swimming out with the 50s?

You have to do the math. SAC rate, Swim Speed, Difficulty of the dove. Familiarity of the cave.

Remember 20 years ago lots of people were taking a single LP104 with a Y-Valve on Intro to Cave dives just fine. And an LP104 with a Yvalve isn’t true redundancy like twin lp50s

So, pumped up lp50’s might be 72cu’ for each. 144cu’ total. 48cu’ of penetration at .5 sac rate with a 50fpm swim speed in 100’ of water is 600’ of penetration.

Of course what is your buddy diving for the purposes of gas matching?

Imagine you’re at peacock. Say average depth 45’, same sac and you’ve got over 1000’ of penetration. I got no problem with that. But add a CCR and now at Ginnie you can swim the entire map this side of 2000’ and at Peacock with multiple exits, you have enough bailout to swim the entire map.

I can show you the math if need be.

 

[grantctobin]

So, pumped up lp50’s might be 72cu’ for each. 144cu’ total. 48cu’ of penetration at .5 sac rate with a 50fpm swim speed in 100’ of water is 600’ of penetration.

To what pressure do you think filling LP50s gives you 72cu?

 

[lostsheep]

To what pressure do you think filling LP50s gives you 72cu?

32% at 4000psi assuming a z factor ~1.05 should be close to 72 cu ft


.

 

[Superlyte27]

To what pressure do you think filling LP50s gives you 72cu?

Do the math.

 

[grantctobin]

Do the math.

I am quite confident in my math. I am asking you what pressure that means, to you, as most cave instructors in Florida aren’t super familiar with gas compressibility formulae.

 

[inquis]

assuming a z factor ~1.05

Higher...

 

[lostsheep]

Higher...

Looks like you’re right, I was going from memory. 1.07-1.09 ish ? FWIW, that’s still in the 70 cuft range which I’ll call close enough to 72 for scuba math.

 

[Superlyte27]

I am quite confident in my math. I am asking you what pressure that means, to you, as most cave instructors in Florida aren’t super familiar with gas compressibility formulae.

Do I strike you as most cave instructors?

 

[grantctobin]

Do I strike you as most cave instructors?

I’ve generally found them happy to explain things and even happier to be correct when explaining something. That said, what pressure in an LP50 (to you) equates to 72cf of gas? We can assume say, 15°C temperatures but happy with even the usual FL springs temperature.