Deep Diving Gas Planning

[DevonDiver]

Wow, seriously? I made this post with the honest intention to start a discussion on the merits of my thought process before I begin my planning in addition to other sources.

I've already had it pointed out that my train of thought was flawed, so was that really neccessary?

I think the point being made was that you were over-reaching the level of diving for which you are trained and adequately experienced. It is dangerous to do that.

Many experienced divers do get exasperated when less experienced divers try and run before they can walk. This is especially true because of the 'you don't know what you don't know' factor.

Consider the training that you've actually been given. This training provides a very good indication of your limitations. If your goals exist beyond the capacity of that training, then seek further training or dive with a suitable mentor.

 

[Garth]

How many of those dives were in a drysuit? And I too wish to here about how you would calculate your gas management. If you don't know your sac rate what SAC rate would you use to plan your dives.

 

[OldFNG]

I'm curious, could you please explain how you calculate your gas and plan your dive on a dive such as one you described previously? I too think you have way too few dives to do dives such at these.

P.S. The PADI Deep Diver specialty is usually crap and doesn't give you near the knowledge or skills needed to safely dive deep in my opinion.

I'm realizing this, on that topic, I have been looking at SDI/TDI for the deep dive courses they offer, how hard is it to go from PADI to SDI/TDI if I am looking for a more comprehensive course after I log a bunch of shallow dives.

 

[nadwidny]

I'm realizing this, on that topic, I have been looking at SDI/TDI for the deep dive courses they offer, how hard is it to go from PADI to SDI/TDI if I am looking for a more comprehensive course after I log a bunch of shallow dives.

At this stage of your game I would suggest to dive more and worry about courses less.

 

[Troutmaster]

Old FNG,

Your are clearly excited about diving, and that is great.

As others have said, sling a pony and forget about the "hang gas" on a bouy.

Most importantly, you need to slow down. Alot. I had HUNDREDS of dives when I switched to a drysuit. Everything is harder to do with thick gloves and cold fingers. It was a whole new ball game, you need to start with some pool time and then some shallow dives. Cold water is alot different from warm water. 120 fsw warm and clear is an easy dive. 120 ffw at 38 degrees and limited vis is a no-bulls@#t dive. If you get yourself a "dark narc" it could have very bad outcome. You have alot of diving ahead of you, learn slowly and in shallow water until you are ready to move to deeper, colder water.

You need to plan your dives for the elevation and depth you are going to dive. And as was said many times, you don't "find" yourself in deco. You put yourself in deco. As I am sure you are aware staged deco dives are well outside your training and experiance level.

It is very easy to go to TDI from Padi. Most of us in the tech relm have cards from multiple agencies.

Take your time in your learning curve. Diving is not a race to the end, and if you turn it into it one, you might find yourself at the end WAY faster than you want.

 

[Garth]

Great words of advice Mr Trout catcher. That is what i was trying to say, but he still hasn't told us how many drysuit dives he has done.

 

[nadwidny]

Old FNG,
Most importantly, you need to slow down. Alot. I had HUNDREDS of dives when I switched to a drysuit.

If he wants to get hundreds of dives in the local environment he needs to get into a drysuit sooner, not later.

 

[UCFKnightDiver]

Great words of advice Mr Trout catcher. That is what i was trying to say, but he still hasn't told us how many drysuit dives he has done.

Nor how he plans his dives, shrugs. I'll also say deep on air (no helium) is not the answer.

 

[Troutmaster]

If he wants to get hundreds of dives in the local environment he needs to get into a drysuit sooner, not later.

I should have been more clear, he should be diving a drysuit. My point was I was a much more seasoned diver when I made the switch from wet to dry and the transition was still a challange. My point was that he needs to work out the kinks with the drysuit before he does any "big" dives in it.

 

[leabre]

I only read as far as the first page, I can already see where this discussion is going.

So, with so few dives it's somewhat predictable the perceived need for all kinds of additional air sources and emergency contingencies. As you gain more experience (that includes gas planning, management, and proper execution of plan) you'll find it's really not a big deal. You plan for it and execute the plan.

Generally, for any planned dive (NDL or otherwise -- but in your case NDL for sure) you carry as much gas as you need to complete your dive and, at the deepest part of the dive to share air with him on an ascent in case he loses his gas supply, and he'll do the same for you. This conceptis called "Rock Bottom" in case you with to further research it.

There really isn't a need to carry an addition gas source (pony) or hang an 80 at a shallow deco stop just-in-case. If you need more air, take a set of doubles with you.

So how do you compute it? At sea level and salt water...

Assuming 100', we'll assume during an emergency SAC of 1.0 and an average ATA of 2.5 (= 50' average) during your ascent.

Assuming you ascend at 30' per minute from 100' to 20' to do your safety stop, and 1 minute at depth to execute the air share...

1 + 3 (100' -> 20') = 4 minutes + 3 min safety = 7 minutes + 1 minute ascent = 8 minutes grand total. DCR = SAC * ATA = 1.0 * 2.5 ATA = 2.5 CF/min

2.5 CF/min x 2 divers = 5 CF/min x 8 minutes = 40 CF.

If you're using an AL80 at 3000 PSI, then 40 CF reserve equals 1500 PSI. This means at 1500 PSI you begin your ascent or you are burning your buddies gas in case of emergency. I am simplifying greatly because an AL80 is actually 77.5 CF, not 80.

Think this number is too conservative? Practice it sometime, you'll find it's very accurate. This means your own ascent will consume about 750 PSI if you take 8 minutes from 100' to surface (maybe a little less if you're not stressed or cold or over worked).

So, if you have only 40 CF with which to conduct the dive, how much time can you get at 100' depth? Well, we use .75 SAC (conservative, but easy to work with). 100' = 4 ATA, so .75 * 4 ATA = 3 CF/min. So that is 30 CF for 10 minutes at 100', 13 minutes for 40 CF, but you figure 3 minutes to descent, leaves you with 10 minutes at depth, and you're 8 minutes to surface... will lave you with about 500 - 700 PSI remaining on an AL80 without emergency and 0 PSI with emergency air sharing from maximum depth.

Using air and want 20 minutes at 100'? You'll need a 100 CF tank to execute the dive properly. Don't forget to adjust for altitude and fresh water. I do my stops differently, I would take a minute to share air, ascent for 2 to 50 ft., then 10' /min thereafter which leaves me with 8 minutes as well, just using deep stops instead of shallow stop.

Let me know if you have any questions