I will be diving 130s tanks on a trip and will be diving at depths over 100 ft. We will be diving nitrox and I know I will run out of no deco time before air time so when im at a certain depth and my no deco time runs out, I need to simply go shallower to have more no deco time right? Prob a silly question but im just makin sure im not making a mistake. You should definitley start ascending slowly and start making your way up to the boat right? Just in need of clarification. I have never dove with large tanks like that
No deco and dive computers
- Thread starter wmason11
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Tank size is meaningless other than it may allow you to get closer to killing yourself by going into deco for which you are obviously not trained. Have you planned the dives on tables and know what your NDL's for each level are? What's your SAC rate? Are you sure you will have enough gas for the dives you'll be doing. How many dives per days. What do you expect your CNS clock to look like after each one?
You are talking about making a multilevel dive. Seems you are not trained to plan for that either. Before you go doing these dives I'd advise you to forget the computer and get out some tables and start refreshing yourself on how to plan multilevel dives. Then plan those dives and stick to the plans you make. Use the computer as a depth gauge/bottom timer.
You are talking about making a multilevel dive. Seems you are not trained to plan for that either. Before you go doing these dives I'd advise you to forget the computer and get out some tables and start refreshing yourself on how to plan multilevel dives. Then plan those dives and stick to the plans you make. Use the computer as a depth gauge/bottom timer.
chrpai
Contributor
I find this interesting. I think the vast vast majority, including myself, of recreational divers have never had formal training in planning multilevel dives. Am I wrong? My experience is that very few take the multilevel diver speciality, that the "wheel" is OBE and that after learning how to plan square profiles divers are given a computer and go "oh, I go up a bit and I get more time... ok".
Other then understanding RMV and the concept of rock bottom gas planning, ( I use Lamar's simplified formula on an AL80 of 100 psi for every 10' of depth + 300 PSI or 500 PSI whichever is greater ) ...... is there really anything else to know?
Don't get me wrong, you give good advice, but it seems disconnected from everything I've observed over the last 12 years.
I would pad this a bit and always keep about 5 mins on your NDL, that way if your computer does give out a depth you can ascend with a buddy a do normal safety stop at 5 metres. Rather than have to guess about how much deco time you accrued by running it to Zero.
A simple 30m, 20m 12m multilevel profile based on the PADI Wheel/RDP is a good plan to have scribbled on a slate somewhere so you have a rough idea about NDL times at each level, but also set an air setpoint as well.
For Example (without checking the RDP)
30 metres for 10 minutes or until air hits 120 bar
then ascend to:
20 metres for 10 Minutes or until air hits 90 bar
then ascend to:
12 metres for 30 minutes or until air hits 70 bar.
Safety Stop
When I took my PADI OW in 2004 planning multilevel dives on the RDP was included. It can be done and the wheel was not necessary. Even after the ERDP came out we still figured out how to plan them on it. You did use a little conservatism, which should be done anyway, but times came out with a minute or two of the wheel.
I cover it in my OW classes.
I cover it in my OW classes.
chrpai
Contributor
My OW was in 2000 and it was not covered.
Is this part of the standards or just something extra you cover?
Is this part of the standards or just something extra you cover?
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flots am
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It depends on how long you stay and at what depth, and what computer. Ascending a little might give you more no-deco time or it might give you a warning about a hard ceiling and a deco stop.
If you're not trained for decompression diving and couldn't handle a complete loss of your tank while you have a significant deco obligation, I would suggest staying in within the no-deco limits. It really sucks to have to make a choice between "bent," "crippled" or "dead."
Also, not all computers are designed to properly handle a decompression dive. Some just have a "you screwed up" mode and will attempt to get you back to the surface alive, while others will actually calculate proper deco stops. Additionally, not all computers will correctly calculate the remaining gas, to get you through your deco stops before your tank is empty. In fact, some will happily tell you that you have a 20 minute deco obligation and 5 minutes of gas left.
Plan a dive you're qualified for, and dive the plan, even if the plan is as simple as "Start ascending @ 1000PSI or 10 minutes of no-deco time, whichever comes first"
If you're going to do a decompression dive, I'd suggest planning it ahead of time with something like VPlanner and taping it to a wrist slate. That way before you ever get wet, you'll know how much gas you need to safely execute the dive and how long you'll need to stay at each depth. This eliminates "surprises" from your computer. You'll also need to have a relaible buddy with a compatible gas plan, or at the very least fully redundant tanks. Running out of gas before ending the dive is bad.
flots.
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altaskier
Contributor
You also need to know what the hard bottom depth is, what your nitrox mix is, and so on. And have you calculated your SAC before? You know the details of your dive, so you should plan this out; you can always come here if you want someone to cross-check your numbers.
OkByMe
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Please don't take offense..
Dude! If you have to ask that question, you definitely need to review the basics for your own safety. I suggest you get down and personal with the tables. Even though I dive with computer and analog backup... I still carry the tables S**t happens. You can use the tables based on the available air supply at depth to plan a rough multilevel dive if you know your nominal SAC rate and track your at depth times. But that is not exact enough for you to get full use of the available volume of air and will get you in trouble. you could exceed your time at (any) depth with that much air. Assuming your ARE going to 100+, that puts you at NITOX MOD 28% @ 130 and would have to plan TAD accordingly.
If I were you and you have not made up your mind on the computer to buy or are not in a position to buy one yet, RENT ONE. You are spending your time and money for a dive trip and have some big honk'in tanks to dive with... Get the most out of your dive safely with a computer. Always carry a timer, depth gauge and pressure gauge with you and a slate to note your times at various depths in case the computer bites the dust. If it does and you abort the dive, it will help in determining the repetitive dive cycle (Average depth) so it does not end your diving day.
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