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Recreational Dive Planning software?

Discussion in 'Dive Software' started by stuartv, Feb 12, 2015.

  1. tbone1004

    tbone1004 Technical Instructor ScubaBoard Supporter

    # of Dives: I'm a Fish!
    Location: Greenville, South Carolina, United States
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    mindeco is an approach of calculating deco based on depth and time, similar to ratio deco.

    The math to calculate it yourself is pretty simple actually, but you can estimate it. I got that number based on 60fpm descent rate, 30fpm ascent rate, 12 minutes on the bottom with whatever sac rate I quoted, I have an excel sheet that has all of these formulas in it that I made. You aren't doing 4 dives a day below 80FSW without doing deco, just isn't going to happen.

    Yes the EAN32 is due to PPO2, EAN30 is fine, PPO2 of 1.4 is maximum recommended for diving, 1.6 for deco, and most guys try to keep it around 1.3 for CNS clock when you're doing that much bottom time.
     
  2. stuartv

    stuartv Seeking the Light

    # of Dives: 200 - 499
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    Huh? Did I misunderstand? I understand tbone to be telling me that, diving with a single AL80, I'm going to run out of air way before I hit a NDL, so I WON'T have any issues with incurring deco.

    As Lorenzoid already observed, I don't know a way to use my PDC to plan the 4th dive in a day when I haven't even done the first dive yet.

    And when has the SB response ever been "you're doing too much to plan your dive"?!?! Wow!

    I understand that thing could change, etc.. I also understand that once I go out and actually attempt to do one day of diving as described, I'll probably learn everything I need to know to allay any future concerns about wanting to do this kind of planning.

    I could have just come here to SB and asked "can I do 4 dives in one day, with blah blah blah specifics". But, to me that's not a lot different than doing a Trust Me dive. Instead, I'd rather learn how to answer the question myself (and do so more easily than a bunch of really tedious work with dive tables).

    I have read up on Rock Bottom calculations enough to understand the basic concept. But, at this point, I am pretty comfortable with doing NDL dives without being that conservative on air. The dives I've done so far, the DM always tell everyone what the min gas is and I have no problem thumbing the dive if I'm the first one to hit the min.
     
  3. tbone1004

    tbone1004 Technical Instructor ScubaBoard Supporter

    # of Dives: I'm a Fish!
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    you're doing too much planning because you're planning is not realistic for the diving you're doing. Estimating is close enough, and you're going to run out of air on the first one, but you'll rack up a boat load of deco doing multiple dives.

    You should be doing rock bottom on all dives, whether the DM tells you otherwise or not, it changes based on your planned depth, but it's not "being that conservative" it is being safe....
     
  4. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
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    You are well-advised to say away from PPO2 of 1.4 as a bottom gas....and I think you'll find most operators in Hawaii will not be able to provide you with custom mixes like 30% without considerable extra charge. To be clear: I think 32% at 120 ft is over the line. If you aren't at that depth long, if you are not building up any CO2 by working hard, you may well be OK. I would not do it, if it were me.

    It is not hard to work out your gas needs. Figure out how many psi you are willing to use from your AL80 (like 3000-700 = 2300 psi to be used), figure out what fraction that is of your AL80 (like 2300/3000 x 77.4 = 59 cuft to be used), work out how many *surface* minutes that is from your RMV (like 59/0.8 = 74 minutes), and then estimate your average depth and pressure on a dive, say to 100 ft (like 100/33 + 1 = 4 ATA). If the ENTIRE dive were at 100 ft, you'd have 74/4 = 18 minutes of gas. So you can forget a 20 minute dive to 100 feet, if you're going to spend all your time down there. 120 feet is worse; you'll only have 16 minutes of gas. Of course, you'll spend some time getting down there, and some time coming back; the softwre makes that part easier. But imagine you are coming up at 30 ft/min from 120 ft; that is 4 minutes, at an average depth of 60 ft, so it takes 9 cuft of your gas supply just to get to the surface...that will show up in your AL80 as 350 psi to get to the surface....so now you know you need to leave the bottom at 1050 psi remaining, not 700. Oops, now you want to do a safety stop for 3 minutes at 15 ft; that takes another 45 psi in your AL80, so you better leave the bottom with 1100 psi remaining.

    Guess why you use software. Too many little things you might miss, or calculate wrong.
     
  5. stuartv

    stuartv Seeking the Light

    # of Dives: 200 - 499
    Location: Manassas, VA
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    Okay, so I'm not trying to argue with you on this (and I think you both know me well enough now to understand that). I'm just asking to understand better.

    When I took my Nitrox class, we were taught that 1.6 ppO2 is the Max anyone should ever dive to, and that 1.4 is what is recommended for people to stick to. The instructor gave an example, which I will slightly adapt here. He said:

    "If I'm diving EAN32, with an MOD of 111' (ppO2=1.4), and I go down to 111' with my expensive camera rig in a spot where the bottom is 120', and if I then accidentally drop my rig and it's sitting at 120', am I going to go down and get it? Yes."

    What do y'all think of that?
     
  6. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
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    If your instructor said he was going to enter the water with a giant stride from a 10 ft high dock, while holding that expensive camera, would you do it too?
     
  7. Lorenzoid

    Lorenzoid idling in neutral buoyancy ScubaBoard Supporter

    # of Dives: I just don't log dives
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    Are you diving independently (i.e., shore diving, off a private boat, etc.) or are you diving with a dive operator? If the latter, THEY know what a "reasonable" plan is. I'm sure I'm not saying anything you don't already know, but a dive op that signs you up for a 4-dive day will give you a rough estimate of what kind of dives those will be, and you can be fairly certain you will not exceed NDL's--that's part of their job. For example: "Our first dive will typically be a wreck in the 90-120 foot range, followed by a reef dive, and in the afternoon we will do ...." Unless you are diving independently, you won't run into a case of not being able to do the fourth dive of the day if you book with a regular recreational dive boat operator. Dive ops want repeat customers, not pissed off ones or bent ones. They are not going to let you push the limits too hard.

    As for gas planning, the abbreviated answer is that you could use your expected average depth. But for recreational dives, the dive op is going to give you a fresh tank for each dive that the dive op knows has enough gas for you to do what you signed up for, more or less.

    I know we so often hear the advice to not rely on dive ops and their DMs to keep us safe, but realistically, they're going to keep you in the ballpark. They want you to do that fourth dive if that's what you paid for.
     
    tursiops likes this.
  8. stuartv

    stuartv Seeking the Light

    # of Dives: 200 - 499
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    That is something I feel adequate to judge as a bad idea. Being able to judge diving to a ppO2 of 1.5 is not something I feel especially well qualified to do. All I can go on is what I was taught in the one class I took. So, my question about going to 120' on EAN32 does not seem like a fair comparison to a giant stride off a 10' dock with an expensive camera.

    And that is why I asked for your opinions as, generally, those of you that are responding in this thread are people whose opinion I have developed some respect for.

    ---------- Post added February 12th, 2015 at 05:27 PM ----------

    I understand that. That doesn't quench my desire to work it out for myself. And do it more accurately than quick and dirty estimates. tursiops' comment about why we use software and little things one might miss or calculate incorrectly is exactly why I started this thread to inquire about software.

    As I gather that there is no software that does exactly what I want, I am now contemplating whether I want to just write it myself. Software design and development is what I do for a living. None of y'all would want to use it, but maybe other new (and new-ish) divers like me might like it.
     
  9. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: U.S. East Coast
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    Well, you've gotten your answer, several times. Don't do 1.5, stay away from 1.4. Let your instructor go get his own damn camera from 120 ft, don't do it for him!

    The jumping off a dock question is about risk management; doing that there is a good chance the o-rings will leak and flood the camera. But not always.
    Going to 120 on 32% is increasing the risk; where do YOU want to draw the line? The risk curve starts getting pretty steep after 1.4, and is unacceptable after 1.6.
     
  10. Lorenzoid

    Lorenzoid idling in neutral buoyancy ScubaBoard Supporter

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    If someone else hasn't already mentioned it, a ppO2 of 1.2 is generally considered the conservative value, 1.4 is generally considered moderate, and 1.6 is considered the limit of safety. I'm a rec-only diver, but it's my understanding that divers will push a ppO2 of 1.6 on deco stops because the theory is that remaining still and calm lessens the potential for oxygen toxicity. If MY camera were to drop to 120 feet while I'm breathing EAN32, I would not chase it, since that involves significant exertion, and it's uncertain how long I will be down there picking it up. I might risk a brief exposure to 1.6 if I were not exerting myself much, but it all depends on how brief and how much exertion, and those are difficult to judge in your hypothetical scenario. I wouldn't risk it.

    ---------- Post added February 12th, 2015 at 05:37 PM ----------

    Fair enough. Knock yourself out, man.

    Part of the pleasure of recreational diving is NOT having to work this stuff out.
     

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