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Dive Planning

Discussion in 'Technical Diving' started by Jenkins, Sep 28, 2009.

  1. Jenkins

    Jenkins Friends, Romans, countrymen, lend me your ears.

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    Comments on another thread got me thinking about just how important the old mantra "plan your dive, dive your plan" is and how much more discipline is needed once you move into decompression diving.

    OK I admit on shallow dives I jump in the water, bimble around keeping an eye on my computer to ensure I don't exceed the NDL (or the MOD of my gas mix), monitor my contents guage and surface when I'm getting low(ish) on air. Dive planning is minimal as my "bailout" should anything go seriously wrong is to abort the dive and head for the surface.

    Moving into techy diving and suddenly my dive plan is written out on a wrist slate, giving a minute by minute account of what depth I should be at every point of the dive. I use the PC to calculate my deco schedule and gas consuption, carefully ensuring I have at least a third of my backgas in reserve. Yes I dive with a computer but I also carry a D-timer and wrist slate as backup, simply aborting a dive is no longer an option as sometimes by the time I get to the bottom of the shotline I am already into deco.

    Personally I would be looking to use Trimix on cold water dives deeper than 35m, I have been to 40m on air and didn't enjoy the experience. When using Trimix I set the narcotic depth (how narked I am) to the equivalent of diving to 25m on air, as by 30m I can feel the effects of narcosis and with all the other pressures of a deep dive I don't want the added complication of being narked.

    Once in the water exceeding my planned depth will totally ****up my deco schedule so is an strict no no, and the same goes for over staying my planned bottom time. Messing up my deco schedule not only makes my carefully calculated wrist slate useless but also (very importantly) means that I may not have sufficient gas to complete the dive.

    In any form of Nitrox/Trimix diving there is the ever present concern of exceeding the MOD of your gas mix and getting an O2 hit. But with techy diving I am normally carrying 3 different gas mixes and switching to/from at the correct depth is vital in order to ensure I decompress correctly (in line with the dive plan) on the ascent. Breathe the "wrong" gas at a given depth and you could get an O2 hit, or find youself breathing a hypoxic mix with insufficent O2 to support you!
     
  2. jb2cool

    jb2cool Moderator
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    I only do min-deco dives at the minute on either air or nitrox. I use a combination of V-Planner and jDeco to plan the dive so i can plan my dive for deco requirement and gas consumption. During the dive itself i tend to use the GUE minimum gas (Sometimes known as rock bottom) gas planning rules.

    I only dive with a bottom timer with min-deco tables written in my wetnotes. My regular buddies both use their Suunto computers. On the stops we use my deep stops (First stop at half max depth and then 1min every 3m from there) and then their longer 5min (We do it between 5m and 3m) stop that their computer asks them for.
     
  3. Air-Guzzler

    Air-Guzzler Cannot spel and I cannut delet your post :-)

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    Jenkins i read your post today anwith d came up with a few un answered questions.

    How do you plan your deco gas

    Do you let your PC choose your stops & not question it.

    Do you accept everything that your software gives you or do you refer back to tables to get a second opinion.

    I see that you never mentioned deep stops how would you calculate this
    50% of your max depth or 50% of your depth to your next gas switch

    from what ive done & read this can be a great discussion point as if you choose 50% of your max depth and use a VR££ its a dead cert that you will bend it.

    How would you handle a loss of deco gas
     
  4. bottlefish

    bottlefish Super dooper member
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    I'll wade in with a few answers of my own, if nobody minds ;)

    I'm not a fan of "standard gases", in my view, this is a lazy way to avoid making an informed choice. Perhaps blue touch paper to any GUE proponents, but hey, there you go ;)

    Bottom mix is based on max PO2 of 1.4, and max END of between 35 and 25 metres (discounting O2 as narcotic), depending on the location and dive etc (e.g UK would tend towards 25 metres, Malta more towards 35)

    Deco gases are chosen to suit the dive, based on;

    Gas consumption, to balance useage across all gases
    Emergency procedures, to maximise options in the case of a FUBAR at depth (i.e. ensure I don't need to travel too far before I can switch on to my leanest mix)
    CNS tox limits
    If going deep trimix, potential PN2 spikes on gas switching for the ascent

    Yep.

    I use vplanner, and IANTD tables, they're both based on VPM, the results are the same. Best fit tables will come on the dive with me as well, just to give me a further option in case of lost wet notes, deviation from plan etc

    deep stop should be mid way between your mad depth and your first switch.

    If you did a deep stop whilst following the dive on a VR3, you wouldn't bend it, the computer would simply treat the dive as a multi level, and recalculate your deco obligation accordingly.

    However if you were to perform a deep stop, based on a plan that didn't have a deep stop included, then yes, you could bend the computer, and potentially yourself.

    The point is, the deep stop gives you a chance to catch up with your off gassing, however it's going to be performed at a depth where you may well still be off gassing, so it could also affect (increase) your deco schedule and run time. So if you want to include a deep stop, you need to include this at the planning stage, add it in to your planning software as a multi level dive.
    I cut various plans, to cope with emergency scenarios, i.e. a single lost deco gas, for each gas I am carrying, a deeper and longer plan combined, to account for what I'd need to do if I stayed longer then my original plan or went deeper.

    Gas requirements and run times are checked for each scenario, if the dive does not feel possible to complete safely, given the emergency scenarios, then I adjust accordingly. Given appropriate gas choices, lost gas scenarios tend to be more balanced, i.e. there isn't too much burden on a single deco gas.

    In a real lost gas scenario, I would also have my dive team to rely on, i.e we'd be able to share deco gas on the ascent and adjust run time appropriately, however I'd also have the knowledge that I could, if needed, complete and required deco schedule on my own, if need be, even if I was to lose a deco stage.
     
  5. Aquafan

    Aquafan Active Member

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    Hi Stu, does your comp bleep at you to remind you where you've got to be at a certain time, or are you constantly checking depth and time and referring to wet notes? I would imagine that if you've just found the wreck there is a small possibility that you may get distracted and stay down a few mins longer or go past your max depth by 1 or 2 m.

    Also I've heard a few diver that dive of slates to pre-arranged depths with bottom timers, why not just use the VR3 to tell you where you need to be, or are the slates just backups?
     
  6. bottlefish

    bottlefish Super dooper member
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    No, all sound on my comp is turned off.... I don't want to rely on an audible alarm, in case it fails!

    So yes, I am constantly referring to my computer/timer to ensure that I don't exceed planned depth or time. It sounds like a lot of task loading, and for sure, the first few tech dives I did, I felt incredibly rushed, as though I was always on the go, just because of the continual checking on arm slate, depth and time to ensure the plan was adhered to. But it feels quite relaxed now, and to date I haven't had to use a deeper and longer plan (i.e. I've never broken the plan)

    If I was to exceed depth, then my next step would be to abort the dive, as I've deviated from plan. Time, again, is not something I'd exceed, regardless of what I see down there... I can always go down for a second dive, but if I deviate from the plan, I'm in no mans land, I've no idea how I'm going to fair in terms of gas management, CNS, and the chap in the boat on the surface is going to get worried when my head doesn't break surface on time.

    If I'm diving on VR3/VRX, then I will prepare wet notes and arm slates with run times before the dive, but conduct the dive following the deco schedule from the computer. The written tables are just there as a backup in case the VR3 fails, in addition the preplanning required to write them up ensures I've validated all of my gas planning, CNS etc. So the VR3/VRX doesn't alleviate the need for pre planning, they just allow you to work within the plan, and given the right computer, provide you more options and more accurate decision making if things weren't to go quite as plan.

    A lot of people still dive purely off arm slates/pre cut tables and a bottom timer... for a start, it's a damn site cheaper (although VR Technologies HNeO computer has opened up the market considerably... awesome piece of kit, if anyone is on the look out for a treasonably priced techie computer!), it also provides conservatism on the dive, you assume a square profile to maximum depth, in majority of cases, you'll be multi-levelling throughout, rarely touching planned bottom. It also keeps the team together, as you are all working off exactly the same run times and stops etc. Finally, it's simpler, and gives you the assurance to review and have some idea of what you'll be doing, where you'll be stopping, before the dive.... running off computer, you'll have no idea where your first stop is until you start your descent.

    The vast majority of my tech dives are run this way, i.e arm slate with a pre cut table and a bottom timer/depth gauge. I've only started entertaining the idea of running off VRX since starting Setinel CCR, where it's obligatory (i.e. I was stuck in the dark ages until I was forced to change ;))
     
  7. Badknees

    Badknees Meg Pilot (retired) and Forum KGB

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    What stu said, but i use pro planner, and add deep stops as a multi level. not to keen in the new pro planner as its not as user friendly, but pro planner wont run on vista :(.

    Andy some comps you can program to remind you of your run time and depth limits. VR3's do not have this function. But if you are doing this or any level of diving you should always know what gas you've got and what depth and time youre running.

    Comps and gas should be checked at least every 2 mins

    Run slates are used with all the info you need depth - stop - run time - gas - bail out - turn point pressure and worn where you can easily read them, mine sits just behind my knuckle on my right arm the same arm as my comps / depth timers. Depending on what you are doing depends on the info on your slate.
    (this is just an example and is not an actual plan)
    Depth = depth so 40m 30m 20m 12m 9m 6m 4.5m
    Stop = time at that depth so 30min 2min 2 mins 2mins 3 mins 4min 18mins
    Runtime = how long you've been there so say you are doing a 40m dive for 30 mins and your deep stop is 30m and is 2 mins your first stop runtime would be 30mins then followed by ascent + stop so your second figure would be 33 mins if you calculate yor ascent at 10m per min
    so 30 - 33 - 36 - 37 - 39 - 42 - 46 - 64
    Gas = gas youre beathing at that depth so say 27% 27% 50% 50% 50% 100% 100%
    bail out = lost gas, deeper, longer so it may be run soley on back gas so it would only include the basics to get you to the surface i personally dont include any deep stops just the basic stops required to safely get me to the surface so 12m - 3 mins 9m - 4 mins 6m - 4min 4.5m - 26 mins all done on back gas.
    my turn presure is based on 1/3 back gas used or 2/3s remaining so if 230 bar it would be 153 bar

    for this example these are just made up figures and are in no way worked out!

    To reduce the possiblity of over run on either time or depth just plan for a little deeper or a little longer than you think you'll need, it's always better to do less than you've planned than go over.

    Slates are used as the plan where computers give you a real time calulation but few will give you your gas comsumption. The slate is the plan with which you've calculated your gas useage, CNS etc on, just flying a comp without a plan will at some point land you firmly in the muck.

    If using the same VPM tables for example VR3 there should be no difference between the two. the beauty of the VR3 is that it will give you best guess if you do happen to bend it.

    My wet notes may have several plans on then and are carried in my pocket but my primary plan is carried on the run slate on my wrist.
    we carry Tables as with wet notes as a get out of jail card for on the fly calculations if the crap does hit the fan and it all goes pete tong youre then giving your self an other chance of getting to the surface un-bent.

    Yeh just read stu again what he said also and and his is less long winded


    BK
     
  8. DeviousDan

    DeviousDan New Member

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    There should be no 'distractions' at depth.

    If your running out of bottom time, don't go ferreting etc.

    If in doubt, call it early. You have to make your dive plan number one priority at all times.

    Dan
     
  9. Air-Guzzler

    Air-Guzzler Cannot spel and I cannut delet your post :-)

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    If you want to hear alarms on a dive then dive with one of these
    [​IMG]

    Computer alarms are a real pain in the ar$e if you have to use one then you have no dissapline.

    I have been on plenty of good dives and had some to$$ers alarm go off and scare the sharks away, as well as other subjects.
     
  10. Aquafan

    Aquafan Active Member

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    Cheers for that BK, lots of good information there. So running slates with the comp when deco diving is essential.
    I'm happy with the no deco nitrox dives for now. Oh and I don't have any alarms set on my comp. :D
     
  11. The Duck

    The Duck New Member

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    I don't tend to post too much but for some reason this annoyed me. If I read the post wrong I apologise in advance.

    Lazy? hmmm.

    Ok, if you want to do "best mix" then no problem. It's your dive and I'm certainly not going to criticise it. However I'd take issue with using a standard gas as lazy.

    I tend to use standard gases (1) as I've been blown out too many times and I can only afford a limited number of twinsets and deco stages. I need to reduce the number of times I have to throw away gas due to ending up diving a wreck that's too deep or shallow (2) for the mix I have. Therefore I've picked mixes that suit the kind of diving that I usually do. Occasionally I do have to pick a mix for a dive that's non-standard but that's an odd occurrence. This is a conscious decision that I consider an informed choice.

    I like using "standard" gases because it has allowed me to end up recognising patterns in the deco, so that I've noticed patterns emerging. This has allowed me to become aware of what my deco commitments should be when planning the dives.

    As for the bit about being a GUE proponent, roughly half my dives are solo and note the VR£ from my last dive :p

    [​IMG]

    (1) I consider a standard gas to be one that YOU have chosen to be standard for you and the people you regularly dive with. for example for some time I used to have 80% as one of my standard gases.

    (2) Too shallow - adding unnecessary deco to the schedule for the mix in question.
     
  12. Razza

    Razza Member

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  13. The Duck

    The Duck New Member

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    Don't worry I've got my gas sorted (though I forgot that I'm doing the night dive at Vobby tomorrow - so I'm going to have to break out the single tank rig for a change :rolleyes: ), so you can borrow my VR£.
     
  14. Air-Guzzler

    Air-Guzzler Cannot spel and I cannut delet your post :-)

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    Hmm Standard Gas mixes.

    I can see both side here TBH as a non GUE diver i would possibly understand Stuarts stance of Standard gases as what GUE class as standard gases.
    On the other hand
    would these not be classes as satndard gases. (taken from Divelife web site)
    30/30. 21/35. 18/40. 14/50. 12/60. 10/50
     
  15. The Duck

    The Duck New Member

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    ANY gas that you use as a standard is your standard gas. It can be air, 22%, 46%, 28/72, whatever.

    GUE tend to use 32, 30/30, 21/35, 18/45, 15/55 & 10/70 - though I believe EKPP have use some other mixes, not sure what though.
    UTD are as above but also include 25/25 (may have others)
    BSAC, from my old Nitrox standard tables, use 21, 27, 32 & 36
    PADI have air, 32 & 36 (NOAA I and NOAA II) for their RDP's
     
  16. bottlefish

    bottlefish Super dooper member
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    I think you're getting over-raught about the phrase "standard gas" and totally missing the point I was making.

    By standard gas I was referring to the GUE use of the term. They don't tend towards certain gases, they will use the same, prescribed gases each and every time, i.e. 100% rich mix, 50% lean with a 21/35 for travel (I think) if the depth and bottom mix warrant it.

    BSAC, PADI, IANTD, TDI etc do not have such restrictions. They may pre-print tables with certain mixes on, but these are favourites, suggestions, not standards... there's certainly no hassle if you decide to use something else.

    You've adopted certain, self imposed "standards" with your gases, based on your experience and diving, however these aren't rigourous standards, you're still up for change (dropping the 80% out of your selection?) if you see the need, you're still thinking about what you can do to improve.

    Hope that clarifies it :)
     
  17. Badknees

    Badknees Meg Pilot (retired) and Forum KGB

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    i would comment but i've had a few tonight so will end up talking bollox well more than normal anyway. I'm with stu on this one. sobber or not and when i can see straight i'll give my veiws.

    KB
     
  18. zoglet

    zoglet Member

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    I've had a few tonight too so I'll jump in while BK's sleeping ;)

    Using standard mixes as Duck says, quickly builds systematic understanding in your head of the deco obligation and profile.

    Assuming you stick with your buddy team throughout the dive, why put yourself in a position where each has a different profile dependent on what was left/blown into their tanks. It also complicates matters if you find you need to share. It's simpler to know that your buddy is doing and breathing exactly what you are.

    I would respectfully disagree with Duck on terminology and suggest a "standard gas", to avoid confusion, is one agreed across a larger group, ie across a team or organisation (eg like the 'S' in ISO - International Standards Organisation). One person has a "preference" or "default". It can of course be standard, but only if it's the same as everyone elses :D

    Each to their own of course, do whatever you and your team are happy with, the key point is awareness and not dyingness. From what I've seen though, standardising across a team just makes things easier.

    Don't take my word for it though (especially as I'm probably far from the best to explain). I think it's natural to believe one system is better than another, especially if a lot of time and money has been invested in it. But I would urge people to take a closer look because it takes a lot of 'unknowns' out of the equation.

    Night night
     
  19. bottlefish

    bottlefish Super dooper member
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    You gain an understanding of likely deco obligations and profiles from doing regular deco diving, regardless of wether you stick to the same deco gases or not. But regardless, whilst you may have a good idea of what looks like a right plan, you're unlikely to use such an intuitive approach to your diving. Deco is calculated and planned, not left to chance, you'll either have it pre written on a slate and/or table, be running off your computer, or be calculating your obligation on the fly (if you're using ratio deco)!

    You're quite right (or should I tone that down, and say I agree?! ;)), of course, and yep, with me the team will discuss gas choices and agree on what's going to be used, everyone "standardises" on the same gases for that dive (apologies, I didn't make the team aspect clear in my original post....).

    However, just to reiterate, this is not the "standard gases" I was referring to. I was talking about the GUE system, and use of the term.

    One thing, for me atleast; what's left in my tanks from the last dive has absolutely no bearing on what I choose and use for the next. If I have unused gas that provides me with an acceptable profile and run time, and the rest of the team are happy to match, then of course I will work it in, but if not, then the gas gets blown off.
     
  20. Jenkins

    Jenkins Friends, Romans, countrymen, lend me your ears.

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    Generally I use EAN30 and EAN70, I prefer to stick with the same gasses for most dives as it means the MOD is imprinted into my mind. If I was diving with just one deco cylinder I would normally go for EAN50. Deco gas consumption is calculated on my buddies (heavier) SAC rate based on the rule of fifths .

    Pretty much yes, although diving regularly I get a feeling for what stops to expect.

    I use Proplanner on the PC and have found that if you add an extra minute to each of the deep stops it almost exactly matches the run time on my VR3. The actual depth of the stops might be slightly out as the computer is calculating in “real time” but I am happy that if I aborted to tables they would get me to the surface OK.

    I cannot envisage any dive where I would choose to leave my deco cylinders on the assumption of finding my way back to them.
    I dive with the valves turned off so freeflow isn't an issue until I come to breathe off them.
    I have practised breathing from a freeflowing second stage and whilst not nice it is possible - I know someone who managed this for 40min on a dive.
    I have a buddy also carrying two stage cylinders, plus we both have backgas.
    Failed O-ring or freeflowing first stage would be a problem – don't fancy swapping regs underwater, but as mine (and my buddies) are all M25 DIN fitting I could swap the faulty one out.
    Generally we ascend via the shot line so, (whilst this would never be something I would rely on) I have other divers from the boat who will also have “redundant” gas.
    Sometimes we have a drop tank on deep dives, if so this is never part of the plan but another option to consider if needed - I carry an appropriate dSMB to reqest this if needed.
    If I end up breathing a non-planned gas I can get my VR3 to recalculate a new profile. If that has also failed (or I was running out of gas) I would stay at 6m for as long as possible and then consider O2 on the surface.
     

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