Deep Diving Gas Planning

[dumpsterDiver]

I would plan the dive so that the maximum possible deco penalty (and ascent) would be doable while breathing only the pony bottle. I would leave enough air in my primary tank to do the maximum deco and ascent that I thought might occur. I would not be dragging another tank on a float for deco.

I don't know about high altitude diving at all, but I suspect that you could exceed the NDL at 120 feet on air pretty quickly and you could rack up some serious deco if you breath slowly and you were warm and calm.

So I would start with looking at the NDL for a dive at 130 feet and see how much air that will take.

Then I would assume that I screw up and over stay my bottom time by 3 minutes.

Calculate how much gas that would take to reach that point. Then I would calculate the gas requirements for an ascent and a deco. Then check if you primary tank has enough capacity to do that.

Then also check if your pony bottle will get you to the surface if you over stay by 3 minutes.

That would be if I was doing the dive solo. If you got a buddy, then it gets even more complicated!

If you can't discipline yourself to not over stay your NDL by more than a minute or two or you don't know how to calculate all the gas volume requirements, then you should probably take another class to find out.

 

[Garth]

I'm sorry if I came off wrong but you mention a lot of things like deco algorithms and gas management and all as if you plan to do a deco dive..

PADI wants a 3 minute stop. There's your deco schedule. NDL for depth is the only thing you need to know. Leave the bottom with 1000 PSI for your al80 or at NDL and you should have no problems.

 

[Garth]

I should have specified that it seemed like you were getting ready for a technical deco dive.

 

[Garth]

Also my other word of advice. Dive shallow first in cold water with your drysuit until your comfortable with water temps.

 

[OldFNG]

I would plan the dive so that the maximum possible deco penalty (and ascent) would be doable while breathing only the pony bottle. I would leave enough air in my primary tank to do the maximum deco and ascent that I thought might occur. I would not be dragging another tank on a float for deco.

I don't know about high altitude diving at all, but I suspect that you could exceed the NDL at 120 feet on air pretty quickly and you could rack up some serious deco if you breath slowly and you were warm and calm.

So I would start with looking at the NDL for a dive at 130 feet and see how much air that will take.

Then I would assume that I screw up and over stay my bottom time by 3 minutes.

Calculate how much gas that would take to reach that point. Then I would calculate the gas requirements for an ascent and a deco. Then check if you primary tank has enough capacity to do that.

Then also check if your pony bottle will get you to the surface if you over stay by 3 minutes.

That would be if I was doing the dive solo. If you got a buddy, then it gets even more complicated!

If you can't discipline yourself to not over stay your NDL by more than a minute or two or you don't know how to calculate all the gas volume requirements, then you should probably take another class to find out.

Perfect, this is exactly what I was looking for, I definately need to do my gas calculations. My biggest concern was exceeding NDL at 120 feet and the kind of deco obligation I can rack up in cold water at altitude. I assume I'm going to make mistakes and needed guidance on how to account for it.

I will definately take your advice though and see about taking a class or looking into a course or even a handy lecture on gas requirements calculations for the new year so I can get it 100% down before I plan my next deep dive.

Sorry to everybody else if it seemed like I was planning a deco dive, far from it, I am planning on avoiding a deco dive but I make the assumption I will screw up eventually.

 

[MXGratefulDiver]

As I read through this I can hear my old mentor Uncle Pug's gentle admonishment ... "rethink your dive plan" ... seems to me you're biting off an awful lot, awfully quickly.

Diving cold water's not a lot like diving warm water ... take some time getting used to dealing with the basic things like hood, gloves, and all the extra weight you'll need to sink the exposure gear you'll be using. Do a few shallow dives first ... and while you're doing that, take some gas consumption measurements and calculate your consumption rate. You may be surprised to see how much higher it is, diving in a cold mountain lake as opposed to the warm, tropical water you said you've mostly done. Go into those deep dives with your eyes open ... and the assurance that you are carrying enough gas before you begin your dive. There's an article on my website about gas management that may provide you with answers to questions you haven't even thought of yet.

While you're at it, practice slinging that pony bottle. I wouldn't count on a hang bottle ... it's a nice concept, but in reality if you ain't carrying it on you, you shouldn't count on it being available.

I think you've got the right idea by asking questions and trying to plan out your gas supply ... I just don't think you've got the tools yet to pull off a deep dive under those conditions. And an internet forum's only going to be able to give you partial answers to your questions ... the other part's going to come from practical application.

Test your equipment thoroughly on shallower dives in that cold mountain lake ... make sure you know how it's going to perform before thinking about taking it deep.

Seen too many people come north with only tropical experience and find some nasty surprises they weren't prepared for ... get in a few "practice" dives shallow, then start thinking about those deeper depths that are calling to ya ... you'll be glad you did ...

... Bob (Grateful Diver)

 

[ianr33]

Are your regs suitable for cold water?

Probably don't want to be at 130 feet in a mountain lake if they are not.

 

[OldFNG]

I made sure I bought cold water regs, and first stages. My planned dive profile for the first few months at about 2 to 4 dives a weekend will be first dive of the day to 80 feet with second dive to the 60 to 40 foot range.

The problems as I see it are, 1) Diving at altitude, most dives in the area will be above 3 to 4000 feet above sea level, and 2) Cold, most lakes are glacier fed, which means 4 degree water.

This leads me to the assumption that I should plan as if I was doing a 130 foot dive in terms of gas consumption and plan for about 20 feet deeper than actual depth based on tables + use a computer based on the sections I've read and altitude training dives I have done.

The other contingency to this plan is dive buddy selection, I am planning on tracking down a buddy that has experience in those conditions. I will also be doing lots of dives in the training lake which has a max depth of about 35 feet with a mean depth of about 20 feet every weekend until the end of the year.

Mostly this discussion was budgetary for new gear as its coming up on bonus payouts. I do like the feedback I get here, but as usual this is the internet and everything will be back checked with research and discussion with an instructor and practice in controlled conditions.

 

[dumpsterDiver]

You will also need a good bit of expereince diving in the 80-90 foot range. In my opinion, once you get much past that, things really begin to get "different" with the narcosis and just mental stress from the dive and knowing how far it is to the surface. If you are still practicing in 40-60 feet, go slow, you probably won't see anything that different below 110 feet anyway in a glacier lake.

That link to air consumption calcs is excellent, but the methodology is pretty much worthless until you have generated sufficient data on your own air consumption rates for various activities. That means lotsa dives in shallower water.

 

[horsediver1]

Just a point to ponder Higher Altitude + Thinner oxygen level+ Maximum bottom time diving + being fairly new diver would anybody else be worried about narcing out at depth.

Oldfng I would agree with NWgreatfuldiver and rethink your plans and do a lot of altitude shallower dives building up to the deeper ones, just want to see you on the SB postings in the future