Multi level dives

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Raphus

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It is not PADI but SSI. And no, I never calculated multi level dives because the rule is that tables should not be used for that. Yet, some people do. Me I have my two DCs.
OK I don't know about SSI, in padi you need to calculate square and multi level dives.

Have a look at eRdpML
It's easier to use then the wheel.
Youtube has good explanation Videos.
Of course in reality no one uses them..
 
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Dody

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Well congrats on having completed your DM. I never dive plan multilevel dives with a dive chart if staying within NDL. Dive computers do that for you in real time. If doing a light back gas deco then deco often clears on my shearwater as I ascend during the dive before I get to the safety stop the Perdix will show DECO CLEARED. I can check if on gassing or off gassing during the dive.

For me I watch CNS and Surf GF and tissue loading on the Shearwater Perdix as all the information is at hand with that DC. I assume you are not going into deco on any of your dives so your DC's should be giving you what you need for multilevel diving.
No, I am not going into deco. I have a psychological limitation with deco. :)
 

Wibble

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Tables? eRDPml? How quaint.

Download MultiDeco (Mac, iPhone, Android, win-dos) — other planners are available — and play with it. Observe the patterns for the amount of NDL time, play with the settings and change things around.

Read Deco for Divers. It’s an interesting read.

And welcome to the world where NDLs are never considered (only bottom time, deco time, dive time and gas consumption matter). Even if that’s not for you, it’s good for you to know these things.
 

Blackcrusader

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No, I am not going into deco. I have a psychological limitation with deco. :)

I have not been diving so I have been planning dives both non deco and deco with different sac rates to see how many liters of air I need for the dives and using different tank sizes and tank fills both air and nitrox 32 and nitrox 40. It's good fun and I use my Perdix for this not tables.

A good friend of mine who is a PADI instructor also had that mindset of not going into deco. Finally she did a side mount and deco course. She still finds she has that don't go into deco mindset if not planned. I think you just need to do more diving and not worry about certs so much. I know I will take the advanced nitrox and decompression course when diving gets back to normal as some of my regular dive buddies and I have some places we would like to do extended nitrox deco dives. As I was initially trained for deco with BSAC I do not have any mental block about planning a deco dive. Good to see you back on the forums.
 

boulderjohn

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The "don't go into deco" mindset combined with the topic of this thread brings me to a tale with a moral about both combined.

I went on a Galapagos liveaboard as a single diver and was roomed and buddied with another single diver whom I had never met before. He was DM certified, but not insured and not practicing. On one dive, as we were getting near the end at about 85 feet deep, he suddenly started swimming rapidly toward the surface. I saw him start and was able to catch up with him at something like 50 feet. I took a hold of him and gave a "what's up?" gesture. He raised his console to show me his computer with a look of sheer terror in his eyes. I knew that computer well, and I didn't see anything of concern, so I repeated the "What's up?" gesture. He started up again, still in near panic. He stopped at safety stop depth, and he again showed me his computer with that same look of terror. It was counting down a safety stop.

We surfaced and were picked up by our panga, at which point he told me what was up, his voice trembling with fear. When we were at depth, he had looked at the computer and realized that he only had a couple minutes of NDL left, and he thought that meant that he had only that time to reach his safety stop without going into deco, at which point he would immediately enter a painful debilitation that would require an evacuation to a hospital. I tried to tell him that as he ascended, his computer had increased his NDL time, which was why I saw nothing of concern when he first showed me his computer. He refused to believe me, and as other divers got on the panga, he repeated the same harrowing, near-death experience story to each of them.

The lessons:

1. In this thread, the OP asked about going near NDL on the tables, ascending a little, and then getting more time. As was true in this story, yes, that does indeed happen, but the tables have no way of measuring it. My research on NDL ascent profiles (and I did research this) indicates that if you start your ascent within NDLs, you can ascend as slowly as you like, and you can even do a prolonged dive experience at a shallower depth, as long as you do not go into deco. Everything changes when you go into deco. A computer will measure that for you; the tables can't. The people who try to make the tables do that may make safe ascents each time, but that is at least as much luck as design.

2. If you do unintentionally go into deco, the computer will safely guide you to the surface, provided you know what that looks like on your computer, and provided that you have enough gas to breathe while doing it. You should be just fine with that little bit of deco time. The tables do not have that ability, so you have to go through a generic emergency decompression procedure and then stay out of the water long enough to start over on the tables from scratch before your next dive.
 
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tursiops

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then stay out of the water long enough to start over on the tables from scratch before your next dive.
...and (RDP) this is 6h or 24h, depending on how long you overstayed your NDL (less or more than 5 minutes).
 

Blackcrusader

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The "don't go into deco" mindset combined with the topic of this thread brings me to a tale with a moral about both combined.

We surfaced and were picked up by our panga, at which point he told me what was up, his voice trembling with fear. When we were at depth, he had looked at the computer and realized that he only had a couple minutes of NDL left, and he thought that meant that he had only that time to reach his safety stop without going into deco, at which point he would immediately enter a painful debilitation that would require an evacuation to a hospital. I tried to tell him that as he ascended, his computer had increased his NDL time, which was why I saw nothing of concern when he first showed me his computer. He refused to believe me, and as other divers got on the panga, he repeated the same harrowing, near-death experience story to each of them..

I cannot understand how he got to be a DM and still thought that having 2 mins to NDL he thought he needed to bolt to the safety stop. How was that not picked up through any of his training? After all did he take people up to the surface who had a few minutes of NDL at 35m depth or shallower depths?

I made this little video to explain to divers who are new to diving or new to DC's as some are even AOW but haven't bought a DC yet that NDL increases as you ascend and not to panic and rush the ascent.

 

Wibble

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2. If you do unintentionally go into deco, the computer will safely guide you to the surface, provided you know what that looks like on your computer, and provided that you have enough gas to breathe while doing it. You should be just fine with that little bit of deco time. The tables do not have that ability, so you have to go through a generic emergency decompression procedure and then stay out of the water long enough to start over on the tables from scratch before your next dive.

Amusing. DiveMASTER who knows nothing about diving... hmmm...


For those looking to the future, the NDLs are limits that with the correct kit and training aren't limits at all. It's quite normal to spend an hour at 45m/140', but then spend another hour decompressing with half an hour at the final 6m/20' stop for a two hour runtime. Decompression is like chillout time; no telephone to disturb you, no people hassling you. Just a zen-like hover floating weightless in the sea/lake watching your SMB gently bouncing in front of you. It's amazing how fast the time flies past once you stop counting and just chill out.

Obviously for dives like that you must have planned it with the right kit, sufficient reserves and backup kit -- a single tank just won't do. This is where the training comes in. And that too is part of the fun we get from diving.
 

boulderjohn

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I cannot understand how he got to be a DM and still thought that having 2 mins to NDL he thought he needed to bolt to the safety stop. How was that not picked up through any of his training?
When I originally planned my post, I had this covered, but forgot it. Perhaps it is better here. The answer is that I am not at all surprised, I think similar beliefs are common, and it is a natural product of scuba education, at least at that time.

1. He was trained with all decompression planning at all levels was taught with tables. Computers were not mentioned, even though by then that was what divers actually used. So he was using a computer with table mindset.
2. As was discussed in this thread, table training is to get close to NDL and then ascend at what we now consider to be a pretty rapid rate--60 FPM. That was all that was taught, because tables could not do it otherwise. I learned a year or so ago that PADI learned during the RDP research that slower than 60 FPM, even much slower, did not make a difference, but they did not teach that, probably for simplicity sake. Their training was just don't go faster than 60 FPM.
3. All recreational training is highly focused on one main idea: do not go into deco! Even though we say the first rule of scuba is don't hold your breath, after we say that it is barely mentioned, even though serious lung overexpansion injuries are for more common than DCS. In summary, we scare the crap out of divers about going into DCS without making much of a deal about rapid ascents. There have been many ScubaBoard threads in the past about divers making a rapid and dangerous ascent to the surface, possibly holding their breath, in order to avoid going into deco. I have told this story many times in such threads.
 
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Dody

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3. All recreational training is highly focused on one main idea: do not go into deco! Even though we say the first rule of scuba is don't hold your breath, after we say that it is barely mentioned, even though serious lung overexpansion injuries are for more common than DCS.
I would say yes and no. I think that the reason why we emphasize so much on "don't go into deco" is the fact that if you are in deco, you can't go straight to the surface in a controlled manner without having to stop because of the risk of DCS.
I mentioned a psychological limitation in my case. I would not go into deco without full redundancy and I am not trained in twinset, sidemount or any other technique that for my understanding are more technical than recreational. Maybe one day.
 
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