Question about learning deco procedures

[boulderjohn]

Maybe I'm wrong but the physical part of deco diving is easy

It really isn't. Doing valve shutdown drills without changing position in the water with backmounted doubles while wearing a drysuit is very hard. Holding decompression stops for extended periods of time is very hard.

 

[boulderjohn]

To give you an idea of how things have changed in recent years....

I do a lot of decompression diving in South Florida. About 6-7 years ago, everyone--and I mean everyone--showing up on a boat for such a dive arrived with written plans all ready to go. Many of them had been printed out on a computer printer and then covered with clear tape on a late. Everyone used a bottom timer or computer in gauge mode to guide them on their plans. On one memorable dive, my buddy and I were following V-Planner (which nearly everyone else was using) schedule that way, but he had just picked up a Suunto HelO2 tech computer, and he wanted to see how it worked. We ended up following it instead of our dive plan, and we ended up in the water much longer than our original plan. Back on the boat, people were very critical. What the Hell are you using a dive computer for, you blithering idiots?

I still dive the same boats with many of the same people when I am in Florida. Before the dive, the DM walks around to the groups and asks for their dive plans, and you here the same thing from just about everyone. I have not seen anyone with a pre-planned written schedule in years. Many will consult their cell phones when asked. I would say 90% are using Shearwater computers, and many (perhaps most) have another one for backup. I would guess that the overwhelming majority are using Bühlmann with GFs, and I would say from the fact that most of us end up with roughly the same schedule, most of us are using about the same GFs.

 

[KenGordon]

I haven't bought V Planner or planning software yet but will and am curious as how much that effects a plan.

How does your GF effect plans? How do you choose your GF? Does the GF you choose change if your diving to 150' verses 300'? I dive a Scubapro now but am switching to Shearwater for purely planning purposes.

Some of these questions are why I was so torn about who to go to for the training. I choose to stay local for classroom and some dives but will complete most dives elsewhere. Local is old school thought thou, this whole science of diving is constantly evolving and some new things turn out to be not so right and some to be way better. Deco diving appears to be one huge gray area and I for one really do not want some doctor telling me I can't dive for 30 days cause I just got hurt.

Maybe I'm wrong but the physical part of deco diving is easy - it's the brain part that poses the challenge.

Buy MultiDeco rather than V-Planner. It does GF plans too which is what a Shearwater supports by default. VPM (which is what vplanner uses) is not so fashionable at the moment. You could also play with Subversion which is free.

How to choose a GF is a long and difficult question. However you will find that for medium depths it isn't too important. Really what counts is the second figure (GF high) which controls surfacing over saturation and messing with that will only have a few minutes difference in your final stop. Personally I use 50/80 or maybe 50/85. I'd be happy doing 80/80 but I doubt it would make more than a minute or two difference.

Does your Scubapro support more than one gas? Maybe you should start out using it and a plan on a slate and see how they compare. Then adjust the GF to vaguely match.If your GF plan is sufficiently conservative it will keep you below the Scubapro ceiling. Then in the event of everything going badly you can abandon the slate plans and go with the computer. Kind of one step up from using a bottom timer.

You need a gas plan. This means you need a plan, so 'old school' planning with tables or a desktop computer/ipad is always necessary to make sure you have enough gas for stuff going wrong at an inconvenient time. The skills to do that are the same whether you choose VPM, GF, tables or counting tea leaves to work out the stop depths and time.

I claim that you might as well go with your local instructor as anyone else. They need to get you to understand what you need to make the decisions. They ought not to be saying 'do x, y, z' but explaining how to arrive at that conclusion.

Meanwhile try reading Deco For Divers by Mark Powell.

 

[KenGordon]

I believe that this happens more often than people recognize, and it is a potentially serious problem.

In my first years of technical diving, I used a bottom timer and followed a (usually) predetermined dive plan. Everybody I knew did, and many people still do it that way today. It was years before I saw someone using a computer to guide a dive.

In this system, people usually have a written plan and two contingency plans written on slates or wet notes. Frequently the plans tell them when to leave the bottom and at what depth they should do the first stop and how long to stay at each of the stops. The plans assume that the diver will ascend to that first stop at a specified ascent rate, usually 30 FPM. There is also something called "run time," which is how long the total dive should last, including what time you should arrive at each stop. In theory, if you arrive at the first stop behind your planned run time, you will adjust your stops.

In reality, I know darn well that many people, including me at first, focus on the depth of the first stop and the schedule of the succeeding stops without proper regard to the run time. These divers arrive at the depth of the first stop and begin the predetermined plan for depths and times for the stops, and in some cases they do not realize that they had arrived at that first stop long after the planned run time because of their very slow ascent. I know one specific case in which two divers got bent doing that, as was revealed when they ran the dive profile from the computer they had in gauge mode. (It also revealed that they were deeper than they thought for much of the time, and it showed they miscounted their time on the last stop--all errors that a computer would have caught.)

Divers who do this kind of diving without the ability to check the profile of a computer later may finish many a dive believing they executed the dive perfectly without ever knowing how much they screwed up. "Well, maybe you can make mistakes, but I don't," they can safely say, knowing there is no way to tell if they did or not.

Ascending too slowly is such a common mistake that I can't believe any instructor teaching at this level can fail to point it out. Isn't following the plan a pass/fail item for the course?

 

[boulderjohn]

Ascending too slowly is such a common mistake that I can't believe any instructor teaching at this level can fail to point it out. Isn't following the plan a pass/fail item for the course?

I am not sure I know what you mean by a "pass/fail item for the course." All standards in a course must be met.

I don't know what other instructors do. I suspect it is indeed covered in a course, but once the divers get out on their own, they begin to pick up their own way of doing things. I don't believe there is any course in any subject in which students walk out and go into the real world with a 100% grasp of the concepts learned. In this case, the frequency in which the problem exists suggests to me that most instructors are not emphasizing it enough.

I talked about this with the person who designed much of the CCR training for PADI. It was her opinion that ascending too slowly at the beginning of a dive is the most common error in technical diving. She said that just the day before, she was on a dive in which she ascended at 30 FPM, and in so doing passed almost all the other divers who had started up the ascent line ahead of her. On the boat, she was criticized for ascending too fast. No, she replied, you were ascending too slowly.

A big factor in this is the fact that computers are now being used for guiding dives as much as they are. If a dive is being guided by a computer and the diver ascends too slowly, the computer will adjust the decompression schedule. The computer will, in fact, compensate for a lot of errors that divers who are not using them do not even realize they are making.

 

[ChuckP]

It really isn't. Doing valve shutdown drills without changing position in the water with backmounted doubles while wearing a drysuit is very hard. Holding decompression stops for extended periods of time is very hard.

I'm not downplaying the physical part by any means - I practiced stops on virtually every dive last month and even before that. I understand all these are not task loaded but coming up an anchor line is pretty easy, hanging from a surface marker isn't so bad but where I've really been focusing is trying to maintain with no reference, not looking at others but just staring into blue other than my computer - it takes a lot of focus to stay +/- 1' for up to five minutes, not terrible being +/- 2' but I really need to focus - it seems slightly easier at depth verses 15' but that may just be early thinking. I need to start adding tasks to increase the difficulty though.

Buy MultiDeco rather than V-Planner. It does GF plans too which is what a Shearwater supports by default. VPM (which is what vplanner uses) is not so fashionable at the moment. You could also play with Subversion which is free.

How to choose a GF is a long and difficult question. However you will find that for medium depths it isn't too important. Really what counts is the second figure (GF high) which controls surfacing over saturation and messing with that will only have a few minutes difference in your final stop. Personally I use 50/80 or maybe 50/85. I'd be happy doing 80/80 but I doubt it would make more than a minute or two difference.

Does your Scubapro support more than one gas? Maybe you should start out using it and a plan on a slate and see how they compare. Then adjust the GF to vaguely match.If your GF plan is sufficiently conservative it will keep you below the Scubapro ceiling. Then in the event of everything going badly you can abandon the slate plans and go with the computer. Kind of one step up from using a bottom timer.

You need a gas plan. This means you need a plan, so 'old school' planning with tables or a desktop computer/ipad is always necessary to make sure you have enough gas for stuff going wrong at an inconvenient time. The skills to do that are the same whether you choose VPM, GF, tables or counting tea leaves to work out the stop depths and time.

I claim that you might as well go with your local instructor as anyone else. They need to get you to understand what you need to make the decisions. They ought not to be saying 'do x, y, z' but explaining how to arrive at that conclusion.

Meanwhile try reading Deco For Divers by Mark Powell.

Scubapro G2 supports gas switching, another task that I need to practice. It does not use GF but rather Micro bubble settings, the math is proprietary and won't follow V Planner or Mutideco from what I understand. It's great for the rec diving I currently do, easy to read and understand now that I know it, but I feel that I need to switch for planning purposes - it sucks that there transmitters are also proprietary.

I just started or logged into the training and won't start the class till week after next - there's a lot of good people on here that give answers with the reasoning behind them, and I greatly appreciate that.

Let's see in two weeks how much book smarts I have then we have to apply it in the real world..

thanks all!

 

[DanielRJones]

On my ANDP. Part of my pass/fail was descending at 18m/min and ascending at 9m/min to deco stop then leaving on the second and arriving at next 3m stop in 20seconds leaving 40 seconds of deco before moving on to next stop.

If i had followed my computer i would have been out of the water 4mins earlier as by the time i was leaving gas switch at 21m my petrel 2 had next stop at 6m for 13 where my plan was 1min at 18, 15, 12 and 9 then 15@6

 

[boulderjohn]

If i had followed my computer i would have been out of the water 4mins earlier as by the time i was leaving gas switch at 21m my petrel 2 had next stop at 6m for 13 where my plan was 1min at 18, 15, 12 and 9 then 15@6

I think I got your point, but if my response is not appropriate for it, I apologize.

When preplanning a simple dive using decompression software, you input the planned bottom and depth. The software then gives you are ascent plan. You follow that plan as best you can, but the truth is no one can follow that plan perfectly. If you are diving a perfectly flat bottom, you can come close, but if you are diving a wreck and going through different levels, you may actually be pretty far off. (In my experience, wreck divers end their dives having spent a considerable amount of time shallower than they inputted in their plans.) Many people diving in water with no hard bottom, such a following a wall, will go deeper than planned. (I believe that is because it is common not to add enough air to the wing to get perfectly buoyant when hitting the planned maximum depth.)

Once the planned bottom time is reached, the divers begin the planned ascent. They try their best to ascend at the proper rate, but no one can do that perfectly. They try to hold each of the deco stops at the prescribed depth, but even the best will vary in that at least a little. Put all that together, and you have a reason for the difference. Following a preplanned schedule assumes you did everything perfectly. In contrast, a computer will look at what you actually did for bottom depths, ascent speeds, and depths of stops to tell you what to do.

 

[DanielRJones]

I think I got your point, but if my response is not appropriate for it, I apologize.

When preplanning a simple dive using decompression software, you input the planned bottom and depth. The software then gives you are ascent plan. You follow that plan as best you can, but the truth is no one can follow that plan perfectly. If you are diving a perfectly flat bottom, you can come close, but if you are diving a wreck and going through different levels, you may actually be pretty far off. (In my experience, wreck divers end their dives having spent a considerable amount of time shallower than they inputted in their plans.) Many people diving in water with no hard bottom, such a following a wall, will go deeper than planned. (I believe that is because it is common not to add enough air to the wing to get perfectly buoyant when hitting the planned maximum depth.)

Once the planned bottom time is reached, the divers begin the planned ascent. They try their best to ascend at the proper rate, but no one can do that perfectly. They try to hold each of the deco stops at the prescribed depth, but even the best will vary in that at least a little. Put all that together, and you have a reason for the difference. Following a preplanned schedule assumes you did everything perfectly. In contrast, a computer will look at what you actually did for bottom depths, ascent speeds, and depths of stops to tell you what to do.

No you are correct in all your points and it is why i dive with the comouter but still cut my 5 tables in my wet notes and dive my backup in guage mode.
I was lucky on my andp wthe a straight descent down to a ledge at 43m and then a swim out along a wall so pretty much a square profile.

I will onky stop cutting tables when i buy a second petrel

 

[boulderjohn]

No you are correct in all your points and it is why i dive with the comouter but still cut my 5 tables in my wet notes and dive my backup in guage mode.
I was lucky on my andp wthe a straight descent down to a ledge at 43m and then a swim out along a wall so pretty much a square profile.

I will onky stop cutting tables when i buy a second petrel

Yes. You must have a backup to whatever system you are using for your primary system. If you don;t use two computers, you need to have the written contingency plans and the instruments needed to use them.