check my logic?

[H2Andy]

ok, been thinking about deco diving (i've only done a few), more specifically, gas planning. yes, i've taken the classes. i'm asking to see if what i am thinking makes sense.

as a rule of thumb, i've heard that you can multiply your bottom gas by 1.6 and
get close to your total gas use (including deco). for example, if you're going to
use 100 cf at depth, your total gas (including deco) would be 160 cf.

so i am thinking, what if i double my deco requirement so that if my buddy has
a problem at any time during the dive (expecially right before we turn the dive),
i can share air with him and get him up? (assuming for now similar dive plans and gases).

so ... if i multiply my bottom gas by 2.2 (1.6 for me, .6 for my buddy), i should have
a rough estimate of what it will take for me to (a) do my dive; (b) do my deco; and
(c) share gas with my buddy during deco should they run out of gas.


how does that sound?


i want to do this for rough planning, so that i don't waste time figuring out the gas
needs only to find out i can't carry that much gas anyway. more like a rule of
thumb to get me in the right territory, followed by actual step-by-step gas planning
later.

 

[PerroneFord]

I am not a deco diver, but, I think unless you start carrying AL80s for deco bottles, it might be tough to carry enough deco gas for 2 divers in an AL40. Does the agency you trained with not advocate planning lost deco gas and doing deco on backgas? If you've done your dive correctly, you should have enough backgas to complete your deco obligations.

 

[boomx5]

ok, been thinking about deco diving (i've only done a few), more specifically, gas planning. yes, i've taken the classes. i'm asking to see if what i am thinking makes sense.

as a rule of thumb, i've heard that you can multiply your bottom gas by 1.6 and
get close to your total gas use (including deco). for example, if you're going to
use 100 cf at depth, your total gas (including deco) would be 160 cf.

so i am thinking, what if i double my deco requirement so that if my buddy has
a problem at any time during the dive (expecially right before we turn the dive),
i can share air with him and get him up? (assuming for now similar dive plans and gases).

so ... if i multiply my bottom gas by 2.2 (1.6 for me, .6 for my buddy), i should have
a rough estimate of what it will take for me to (a) do my dive; (b) do my deco; and
(c) share gas with my buddy during deco should they run out of gas.


how does that sound?


i want to do this for rough planning, so that i don't waste time figuring out the gas
needs only to find out i can't carry that much gas anyway. more like a rule of
thumb to get me in the right territory, followed by actual step-by-step gas planning
later.

Here's what we learned to use a couple of years ago. Get the one on dive planning...it may help.

http://www.5thd-x.com/xducation/pdf.html

 

[H2Andy]

I am not a deco diver, but, I think unless you start carrying AL80s for deco bottles, it might be tough to carry enough deco gas for 2 divers in an AL40.

the limiting factor would be gas, not time

in other words, planning is for gas that can be carried, resulting in whatever time
that ends up being

 

[H2Andy]

Here's what we learned to use a couple of years ago.
Get the one on dive planning...it may help.

thanks

what i am trying to do is experiment with another way to calculate and apply
rock bottom

in my case, rock bottom would be the gas needed for me and a buddy to
complete deco safely. i figure worst case scenario is a total air failure right
before we turn the dive, when we have incurred considerable deco obligation.

if from that point on we both have enough gas to complete deco and share,
we should be ok.

my question is, does this sound like good logic, or am i missing something that
i should be including in that rock bottom?

 

[CD_in_Chitown]

Are you saying total air failure before you turn the dive would cost one diver all of his remaining backgas and deco gas?

It sounds like you're reinventing the wheel using an oval shaped template, I mean that in the kindest of ways lil buddy but really, isn't that what rock-bottom is about?

 

[H2Andy]

could you elaborate? that's what i'm trying to think through

i figure that if worse comes to worse, you want to get through deco and
get your buddy through deco, so just double your deco gas.

that way, you'll be covered no matter when the emergency happens

 

[JimC]

It depends on where you want to draw the line. Most people plan for missing deco bottle OR lost back gas.. not both. There is a point where you need to stop and go dive.

 

[diverbrian]

Deco gas management is less strenous for a couple of reasons. The main one would be the fact that you typically won't use that much of it (as you breathe it shallow and at rest) and the fact that there should be plan for "back-gas bailout". I actually use a 1.2 factor to figure how much deco gas that I need and am usually well above that anyways.

Agreed with above post. If you lost both all of your backgas and your deco bottle, you are having a day that even Mr. Murphy isn't likely to cook up. One or the other may happen. Seldom have I heard of both.

 

[H2Andy]

It depends on where you want to draw the line. Most people plan for missing deco bottle OR lost back gas.. not both.

so in that case, you would use 1.6 for yourself and .3 for your buddy? (that is,
they can loose half their total deco gas need (either backgas or stage) and
still be able to complete deco with your reserve.

so.... assuming 100 cf dive, that is 160 cf to get me through deco,
and 190 cf. to get me and my buddy to deco should he lose half his
backgas or deco bottle?


btw, if i could be diving right now, i would be... can't, so am here instead