No deco and dive computers

[BDSC]

so pretty much never get down to 1 min left on ndl time

That will work. You may also be able to set your computer to alarm at certain points. So if it allows you, maybe set it at 2 or 3 minutes to alarm. My Wisdom is set at 5 minutes and even though I may ignore it, I am making the decision to do so and it's not creeping up on me and I forget and am then caught by surprise.

 

[chrpai]

ok thanks for giving me a straight up answer .

There's alot of depth to the question though. Do you know your SAC/RMV rate? Do you understand what rock bottom gas planning is?

Let's assume you'll be diving 32% nitrox with a max planned depth of 110' and your tank is a 3442 PSI 130. At 110' you should start your ascent no later then when you have 1100 psi left. That's about 42CF of gas. As a comparison the rule of thirds ( one for me, one to get back and one for my buddy to get back ) would indicate 43cf but that should be close enough. That leaves you 2342psi to use on the bottom or about 88cf.

Now let's assume your air consumption is .75cf/min at the surface. At 110' ( 4.33ATA) you'll be consuming 3.25cf/min. The NDL for 110' on 32% is 25 minutes. Your suunto will probably give you about 22 minutes in plan mode. With 88cf of bottom gas you will lively have enough gas to put your suunto into deco.

So I'd say when you are within 3 minutes of an NDL or at 1100 psi (which ever comes first ) you start your ascent. If you have plenty of gas left then ascend 10 - 20' and see what your computer gives you for NDL. Repeat this process. Dive until you have at least several minutes of NDL left or enough gas. ( 90' 900psi 80' 800 psi ).

When it's time to ascend, go no faster then 30 feet per minute. Consider a 1-2 minute stop at 60' and do your safety stop at 20'. Then ascend at 10 feet per minute to 10', consider taking another 1-2 minute stop and ascend as slow as you can to the surface from there.

 

[wmason11]

sounds good.

 

[flots am]

I am diving a sunnto cobra 2. I understand all that, I was just makin sure I could go down to 120 for the deepest part of the dive and run my ndl time down to a few minutes left, for example, and then ascend to 100 ft for a few more minutes until time to ascend the line. Basically working the whole wreck using all my available time.

Just to make things even less clear, the "no deco limit" isn't some precise bit of math, science and biology. It's a model of an "average" diver, with a fudge factor built in. There's no guarantee that it will create a safe dive profile for you, on that particular dive.

While many people ride up to the edge all the time, I tend to give it a little breathing room. There's no guarantee that a 3 minute NDL isn't actually a 5 minute deco obligation (or the other way around).

flots.

 

[Lorenzoid]

[deleted]

 

[windapp]

You sound to be very new to diving. The depth limits from your OW course are there for a reason, and you need to inch your way past the 60 ft limit very slowly. You also need to have better redundancy when you go past 60 ft. This means that you must be able to absolutely trust your dive buddy, or have your own redundant air source. If you don't have dives past 80 ft yet, you are definitely not ready for dives past 100 ft. I would recommend not exceeding 80 feet until you get some more dives under your belt, or take a deep diver course. Since you were talking about mult-level diving, that must mean there is something to see at shallower depths. Perhaps you should stick to looking a stuff at those depths. Don't get in over your head, and try to do dives that are beyond your ability.

 

[wmason11]

I have taken te deep course and have made multiple dives to those depths. I however have not made those dives with such a large air supply and having to dive close to nfl times. I will be fine I understand and it's a lot clearer now

 

[lowviz]

...//... But sticking with the initial super-slow ascent rate wasn't causing my Suunto to increase the no-deco time, and I became concerned it was going to count down to the dreaded zero and put me into unplanned deco mode. When I sped up a bit to the normal 30 fpm, the indicated no-deco time indeed started increasing. ...//...

Yes, leave the bottom at 60 fpm until you get to 80% of your max depth. Then follow the 30 fpm rate... Another Way to Look at Decompression | SDI | TDI | ERDI (zip down to the first picture/graph that shows ascent)

...//... I became concerned it was going to count down to the dreaded zero and put me into unplanned deco mode. ...//...

Nothing magical happens.

Just have a plan if you are ever in this situation. The most brain-dead plan for dealing with *light* dreaded deco is to make a proper ascent and suck down every thing you have at 15-20' then surface **SLOWLY**.

 

[windapp]

On a dive with my Suunto D6 (same algorithm as the Cobra 2, I believe) to 110 feet, I was back at the ascent line with four minutes of no-deco time indicated. At the time, I wasn't aware of the technique chrpai mentioned above, where you ascend at 30 fpm to about half your max. depth, then 10 fpm from there to the surface. So at 110 feet I began ascending at around 10 fpm because the instructor I was diving with either was in no hurry to get back on the boat or just generally liked to do the whole ascent slowly. But sticking with the initial super-slow ascent rate wasn't causing my Suunto to increase the no-deco time, and I became concerned it was going to count down to the dreaded zero and put me into unplanned deco mode. When I sped up a bit to the normal 30 fpm, the indicated no-deco time indeed started increasing. So my advice with the Suunto is to not dawdle when it shows you no-deco time in the single digits; get on the line and start ascending.

I still advocate taking a Deep diver course or at least hiring a divemaster and going over a dive plan with him. You'll probably learn something. Dives like this, while hardly the Andrea Doria, still are not something to fly by the seat of your pants on if you haven't done them before.

You need to get shallower than the maximum allowable depth for your current controlling tissue compartment in order to gain significantly more time. This is why the eRDPml has a minimum depth change to consider you to be at a new level on a multi-level dive.

---------- Post added June 9th, 2013 at 09:37 PM ----------

Just have a plan if you are ever in this situation. The most brain-dead plan for dealing with *light* dreaded deco is to make a proper ascent and suck down every thing you have at 15-20' then surface **SLOWLY**.

1. Running out of no decompression time is like running out of air. It should never happen because you are keeping an eye on your computer.
2. Your computer will give you a decompression schedule if you over-stay. Just follow it, and then follow the instructions in the manual for the surface interval afterword.

 

[Lorenzoid]

windapp, I understand it now but didn't at the time, except in a sort of intuitive sense. Deco For Divers was good reading.


I now see on another thread that the OP is doing this as part of a dive shop group trip. He'll be with an instructor/divemaster whom I presume can answer his questions.