Non-technical dive-planning software?

[rjack321]

I will go out on a limb here Daniel and say that deco limits are really not nearly as much concern as you think they are. As a new diver - who is unfamiliar with your own consumption, diving an AL80, even in fairly warm water you just can't get into deco <that> much. Deco is such a wide grey swath it would be hard to accumulate so much deco (ie. 15-20 mins or more) that it would be a big concern if you blew it off.

Running out of gas, because you are unfamiliar with how much you use is really the critical issue. And because your usage is probably highly variable at this time, that makes it doubly hard to know where you are and how much gas you need to make a safe ascent.

You'll easily survive a 5 or 10min deco oops (if you could even accumulate this much). You are alot less likely to survive running out of gas, which all too frequently leads to panic, so-so sharing, breath holding, embolism, and death.

Lamont has a good page discussing alot of these gas volume issues
Rock Bottom and Gas Management for Recreational Divers

 

[daniel1948]

Your software choices are going to be limited unless you consider Mac, Windows, or DOS software. If Linux is your choice, run some virtualization software so that you can run your dive software in a virtual environment.

I'm a Mac fan and run VMware Fusion with several windows guests for corporate and personal use. I also running Sun OS and Ubuntu under VMware Fusion - Just for fun.

I don't like Windows, and that goes for Windows emulation. I use a Mac at home and a Linux box for travel (because the Linux Eee weighs a pound less than the lightest Macbook, and costs a LOT less). But for the dive planning, I'll probably buy that electronic version of the wheel.

I will go out on a limb here Daniel and say that deco limits are really not nearly as much concern as you think they are. As a new diver - who is unfamiliar with your own consumption, diving an AL80, even in fairly warm water you just can't get into deco <that> much. Deco is such a wide grey swath it would be hard to accumulate so much deco (ie. 15-20 mins or more) that it would be a big concern if you blew it off.

Running out of gas, because you are unfamiliar with how much you use is really the critical issue. And because your usage is probably highly variable at this time, that makes it doubly hard to know where you are and how much gas you need to make a safe ascent.

You'll easily survive a 5 or 10min deco oops (if you could even accumulate this much). You are alot less likely to survive running out of gas, which all too frequently leads to panic, so-so sharing, breath holding, embolism, and death.

Lamont has a good page discussing alot of these gas volume issues
Rock Bottom and Gas Management for Recreational Divers

Boy, oh, boy, do I ever disagree with this!!! It's true that decompression is a fuzzy business due to differences in individual physiology, but I'm not going one minute beyond the NDL time my (conservative) dive computer gives me. The risk of getting bent may be small, but the consequences are grave.

As for air time, at the recreational depths I dive, if I start up with 750 psi and make a slow ascent and a 3-minute safety stop, I'm not going to run out of air. And I am very anal about watching my SPG. Equipment failures are possible, but that's why I've got an alternate second stage and a buddy.

The computer or SPG will tell me when I have to ascend. The dive planner (be it software, wheel, or electronic wheel) is to help decide on some guidelines about levels.

Of course, if my computer fails during a dive, I'd abort the dive, surface, and wait until the next day before diving again, using a fresh computer or the tables.

Thanks for the link to the article about "rock bottom" gas management. I've copied the table and will discuss it with the DMs and my potential buddies, and reconsider the pressures at which I start to ascend. (On my group dives, when we went deeper we spend maybe ten minutes at 80 feet, then rose to maybe 40, so we were probably complying with the Rock Bottom table.)

 

[dbulmer]

Daniel,
In line with what Rjack has already said, have you considered what you'd do if another diver is out of air ie not your diving buddy but perhaps someone else?

It's happened to me

 

[RJP]

The computer or SPG will tell me when I have to ascend.

Wow, really?

 

[daniel1948]

Daniel,
In line with what Rjack has already said, have you considered what you'd do if another diver is out of air ie not your diving buddy but perhaps someone else?

It's happened to me

I am a new diver, and I am here to learn. I always figured that the reason they tell us to begin our ascent with 750 psi and arrive at the surface with 500 psi is so that we always have enough air to make a safe ascent while sharing with another diver in an emergency. This is no-stop diving, where a direct ascent to the surface is always safe. Are you telling me that 750 psi is not enough for two divers sharing air to make a safe ascent from a no-stop dive? I'm just going by what I was taught in my certification class and PADI book.

Wow, really?

I watch my computer. When it says 750 psi I ascend. Maybe I should have clarified that my computer has an integrated SPG. So perhaps to be precise I should have said that my SPG tells me when I need to ascend based on air, and the computer tells me if I need to ascend based on NDL time.

 

[RJP]

I watch my computer. When it says 750 psi I ascend. Maybe I should have clarified that my computer has an integrated SPG. So perhaps to be precise I should have said that my SPG tells me when I need to ascend based on air, and the computer tells me if I need to ascend based on NDL time.

Much to learn do you have, young Divewalker.

 

[Gombessa]

Are you telling me that 750 psi is not enough for two divers sharing air to make a safe ascent from a no-stop dive? I'm just going by what I was taught in my certification class and PADI book.

Daniel,

First off, you're on the right track - you're asking questions and questioning answers. That's great. Don't mind some of the cryptic and/or condescending remarks you see here; we're here to help, and sometimes being on this board gives rise to more bizarre forms of levity.

Read over Bob's gas management article, and Lamont's Rock Bottom page again. You'll notice that the amount of gas required for two divers sharing air depends on a number of factors, including depth and ascent rate and breathing rate for two divers (also taking into account that the divers may be stressed during an ascent and breathing more heavily than normal). How many psi that requires depends on what tank you're using (AL80, HP80, LP120?). The point of both articles is that OW divers should be able to calculate the rock bottom for the dive they're going to do. And rock bottom takes into account that all safety stops are followed. Is 750psi sufficient? On an AL80 at 30ft depth with two new divers, probably (but why is it sufficient?). What if you find yourself at 60ft? Or 100ft? Some experienced divers will figure and use a rock bottom of 1600psi for the latter. How would you calculate it out? How much would that leave for the dive, and at what pressure would you then turn around (and is that the same turn pressure you would have used had you not calculated your rock bottom)? Do you see the difference in knowing your rock bottom for each dive rather than just following a "750psi is enough" rule? Just some things to ponder and try to answer for yourself as you peruse the above articles.

Again, it's great that you're actively thinking about potential problems, and looking to learn more--a lot of new divers don't even bother doing that. But rjack has a very good point that as a new diver there's a lot to learn, a lot that isn't covered in most OW certification classes, and at this stage, some safety issues are probably of more immediate relevance than worrying about going into deco.

Cheers!

 

[Blackwood]

Boy, oh, boy, do I ever disagree with this!!! It's true that decompression is a fuzzy business due to differences in individual physiology, but I'm not going one minute beyond the NDL time my (conservative) dive computer gives me. The risk of getting bent may be small, but the consequences are grave.

They [-]are[/-] can be grave. But to re-iterate what Richard was saying, blowing off that little amount of deco is unlikely to yield grave results. Given the breadth of that gray area, someone can get bent while diving within 'conservative limits' while someone else can be fine blowing off 'mandatory deco'.

But the big picture is this: bent is most often fixable, drowned is most often not.

In diving, gas is always the paramount issue.

It's a bit disconcerting that at the common elementary level so much time goes into warning people about DCS (which I believe most divers will feel the effects of to one degree or another) but so little time goes into discussion about gas planning.

This is no-stop diving, where a direct ascent to the surface is always safe.

... in theory

Are you telling me that 750 psi is not enough for two divers sharing air to make a safe ascent from a no-stop dive?

Assuming an aluminum 80, 750PSI is roughly 20CF of gas. Are you comfortable enough sharing gas that your consumption rate doesn't increase with the task/stress? Can the same be said for your buddy? I'd guess: no. So let's say you two are sucking down a combined 2.5CF/min/ATM (SAC rate).

So the question now becomes: What's a "safe ascent"? 60FPM? 30FPM? 30FPM with a three minute stop around 20 feet?

Since you called it "no-stop," I'll just throw out a simple calculation for a constant 30FPM. Say from 100 feet. Since you are going up at a constant rate, the average depth of your ascent will be half the maximum depth, or 50 feet. So the average pressure at which you'll be consuming gas is about 2.5ATM. From 100 feet, it will take you roughly 3.5 minutes to reach the surface at 30FPM. 2.5CFM/ATM * 2.5ATM * 3.5MIN = 22CF, which is a deficit of 2CF from your reserve. And that didn't even account for the "initiating gas share and starting ascent" phase of the emergency, which must be planned for at depth and will only go smoothly if you are both conscientious and competent buddies.

Given those parameters, 750PSI would not be enough gas. What are your parameters?

Edit: Just found this thread. It's an interesting read given our discussion: http://www.scubaboard.com/forums/ne...if-you-new-diver-please-read.html#post4301964

 

[Reg Braithwaite]

Assuming an aluminum 80, 750PSI is roughly 20CF of gas.

Assuming that the SPG is not in error. I have heard talk that some SPGs can be off by as much as 300psi, in which case an SPG reading 750psi may only reflect a tank pressure of 450psi. Oops!!!

I second the suggestion to take UTD's online Ratio Deco class. Even if the OP decides to use other means of planning and executing dives, the course is amazingly informative and can be done on line.

 

[jeckyll]

Blackwood: I'm glad you posted that link to Lynne's thread, I was going to in order to aid this discussion.

I need to find Diver0001's thread in which he listed the areas to be addressed in a crisis in terms of simple ABCD's.

Air
Buoyancy
Communication
Decision
EDIT: found the thread: http://www.scubaboard.com/forums/ba...-managing-task-loading-matter-priorities.html


I think that what we're seeing in this thread is an error of risk assessment, i.e. the risk of DCS is assigned too high a value vs. gas management.

To Daniel: If you have air / gas and you have buoyancy skills, simply following an ascent which includes a 30 fpm rate over 60 feet and stops for 1 min at 30, 1 min at 20 and 3 min at 10 feet with a very slow ascent from 10 feet to the surface should greatly increase your safety. Note that this does mean you need both the "A" and the "B" from the above approach.