When would you head back.......

[King_of_All_Tyrants]

Hi All-

I've got a general question for you all. Let's say I'm diving to 120 feet, with an Al80 that started with 3000 PSI.

At what point would you start heading back to the surface? 1800 PSI? 1200 PSI? More? Less? Would the conditions (i.e. clear, warm sunny vs. low viz, cold, dark) make a difference?

Thanks,

KoAT

 

[TSandM]

First off, I wouldn't dive to 120 feet on an Al80 any more.

But that aside, the information you're looking for is here.

 

[King_of_All_Tyrants]

Perfect. Thanks TS&M!!!

 

[Wildcard]

We take baby divers to 120 on AL80s daily. Some get three mnutes some make the whole 18 minutes.

 

[ZzzKing]

Think of the dive like this.

Descent:
10' / min (I'm slow to equalize) to 120' = 12 min at an average depth of 60'. Say 66' to make the math easy. SAC of .5 yields 18 cuft used. 59 cuft left in your AL80.

Tool around for 10 minutes at 115' (again to make the math easy). 22.5 more cuft gone.

Your buddy shows up emphatically drawing his hand across his throat. Your heart races to match his. Your SAC and his are both now at 1. You give him your octo and spend a minute calming him down. 9 more cuft gone. 27.5 cuft left.

Ascent:
4 minutes @ 30' / min at an average depth of 66 ft with two divers at a SAC of 1 yields 24 cuft. You're down to 3.5 cuft. Kind of cuts into that safety stop, doesn't it?

I'm sure the link that TSandM posted is much more eloquent as well as accurate, but you kind of get the idea from this that 120' on an AL80 may not be a good idea regardless of the visibility, tempurature or weather.

 

[Twiddles]

Start sucking on your BCD? Thanks for the info TSandM, I have viloated rockbottom several times already using that information, I wont do so again.

 

[hvulin]

he never said there was a buddy in the water, so your calculation is wrong!

btw. since you are asking, you should start getting back as soon as you hit 100ft

 

[Tollie]

Hey King,

There are two variables you need to consider. Air (gas) supply and nitrogen absorbtion... Gas reserves and management have been noted but this is dependent on the SAC rates of the team. For some divers with especially low SAC rates attending only to gas supply can lead to trouble with nitrogen loadings... so also consider the tables... which at 120 feet really provide you with very little bottom time without incurring a deco obligation.

 

[Gil57usa]

Hi All-

I've got a general question for you all. Let's say I'm diving to 120 feet, with an Al80 that started with 3000 PSI.

At what point would you start heading back to the surface? 1800 PSI? 1200 PSI? More? Less? Would the conditions (i.e. clear, warm sunny vs. low viz, cold, dark) make a difference?

Thanks,

KoAT

3000 psi or when you reach your NDL, whichever comes first.

 

[Gil57usa]

3000 psi or when you reach your NDL, whichever comes first.

oops, I meant 1000 psi