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Optimal Buoyancy Computer

Discussion in 'Advanced Scuba Discussions' started by rsingler, Mar 23, 2019.

  1. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    Thank you!
    I'll look into it right away.

    EDIT: The OP and I have corresponded on the issue, and have worked out the discrepancy. The current Version 58 in post #1 is okay.
    HKGuns likes this.
  2. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    Thanks to continuing input from our members (thank you @Doctor Rig , @gr8jab and @HKGuns !) we're getting closer to the next revision.
    We'll have fixed that pesky HP80 steel tank error, and added the correct (if rare) Faber MP3180 tank to the mix.
    We're adding a positive buoyancy cell to the Rig tab that will allow you to correct more easily for floaty stuff: buoyancy of double hose setups for the Kraken divers (yay!), buoyancy of some fins, and the necessary addition for those that fly with a Full Face Mask.

    The big change is how we approach fresh vs salt water for your Personal Buoyancy determination.
    The Personal Buoyancy section has been a confusion for many of you, and the way we implemented it didn't help much.
    It's an important area, albeit one that requires a little work in the pool, because there is a big difference between a man or woman who is a big-boned marathon'er, and someone of the exact same height and weight who hasn't got much muscle but lots of um...extra tissue. They need to account for their differing Personal Buoyancy to get meaningful results from the tool, because the difference can be as much as 15lb/7kg!! Mishandling this section was responsible for a lot of dissatisfaction with what the tool said was appropriate, compared with the way folks actually dove.
    So, we're presenting it slightly differently, and recommending a new way of calculating Personal Buoyancy in the pool. If you can't measure yourself, you can always estimate, but realize that it is a key factor for you individually, and is worth determining for future reference as you change wetsuits or rigs.

    Currently testing and doing rewrites of the Users Manual.
    Stand by!
    Thanks again to the SB community for all its input and support.
    RTC'83, HKGuns, stepfen and 3 others like this.
  3. BradMM

    BradMM ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Texas
    I'm still trying to soak some of this in... it's slow. My last dive, I was diving fresh water (72 degrees F), with an old 5 mil wetsuit and a Faber HP 80... and six lbs of weight. I'm a 6'3" 65 y/o male weighing somewhere between 205 and 210. I worked my way down from 12 lbs and the 6 seems to be working. Would that jive with the spreadsheet? I just now downloaded so am not up to speed on how to use yet.
  4. HKGuns

    HKGuns Barracuda

    # of Dives: 0 - 24
    Location: Merica
    A quick check and the spreadsheet has you at 3 pounds.....Probably want to play with it and tune it for your actual setup.
    John C. Ratliff likes this.
  5. John C. Ratliff

    John C. Ratliff Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: Beaverton, Oregon
    Just a quick reply here. My first several looks at the title made me think that someone was selling something that divers really did not need. After reading this thread through, although I have yet to download anything, I must congratulate you (all who have undertaken this effort), as diving has changed so much from my beginning in 1959 to now. In the late 1970s and early 1980s I wrote several pieces on buoyancy control for NAUI News, and actually patented my own BCD (very expensive, as it did not sell), so I've had a concern for buoyancy control for decades.

    This tool will, if used, save lives. I am thinking specifically about the diving accident that occurred with the Arctic ice dive off the USS Healy on August 17, 2006. I made an unsolicited evaluation of that fatal accident, and found a number of discrepencies, one of which was loss of buoyancy control. I sent them to the Coast Guard, but never did hear back from them. In addition to my diving, I have been a Certified Safety Professional since the 1980s (now retired). The divers who lost their lives were extremely negatively buoyant, without a means of getting neutral or positively buoyant.

    Coast Guard Announces Results of Healy Investigation | Coast Guard News

    So I congratulate your efforts, and will be looking at your work more closely in coming weeks.

  6. BradMM

    BradMM ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Texas
    That's amazing! I've been diving since 1991 but am now working on a new cert and am going back over material with a new eye. I've been stuck on buoyancy for quite a while now because it's a lot more involved than I ever gave it credit for in the past. BTW, I'm diving with a ScubaPro Hydros Pro and my Cressi slip-on fins are very light. Thanks to all for this thread!
  7. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    Attached to Post #1 is the latest iteration of our Optimal Buoyancy Computer.

    As always, this product is a group effort, and special thanks go out to @Doctor Rig , @HKGuns , @gr8jab and of course, my tireless friend @stepfen for all their help in making this latest revision an improvement.

    The latest version, and its revised manual, address a real problem we have faced: occasional gross differences between the weight a diver KNEW he required, and the weight the tool predicted. If a diver didn’t enter erroneous wetsuit or drysuit characteristics, this problem occurred due to a lack of proper correction for personal buoyancy. Simply put, some divers with extraordinarily low body fat, heavy musculature and large bony frames are hard put to stay afloat without the redundant buoyancy of a wetsuit or bcd. Conversely, a diver of exactly the same height and weight, but with significant body fat and only modest musculature may have found it quite easy to float during the Open Water Diver 10-minute float test. Thus, two divers of the same height and weight may have significantly different personal buoyancy. Granted, using ONLY height and weight is a fairly coarse measure of potential buoyancy. Body Mass Index (BMI) derived from these same two values is no better.

    Nonetheless, if the same height and weight are entered for these two divers, how is the tool to predict the difference between them? Well, our previous explanation and implementation of the “personal buoyancy correction” was not very clear, and the importance of making this correction was not emphasized.

    In this version, we have added an entirely separate tab titled “Pers Buoy” in which you can compute your personal buoyancy (in a manner not unlike a medical lab measuring body fat). Although the tab itself has brief instructions, it would be better to consult the new manual’s pages 6-8. They explain the theory and implementation of the personal buoyancy correction, which is encapsulated in this graphic:
    We think this new way of computing personal buoyancy will be a lot easier.

    Although the tool and manual urge you to actually measure your personal buoyancy in a pool, there is also a cell in the new tab for you to directly enter buoyancy based upon your past experience. If you’re able to float with your head out of water in a swimming pool if you hold a full breath, you may be about +1lb buoyant in fresh water, and +4lb in salt water. If you float really easily without a full breath, you might be as much as +2 to +10 lb buoyant. If you’re a sinker with heavy bones and no body fat, you are negatively buoyant, and might enter -1 to -6 lb directly in the manual entry cell.

    Additionally, the manual entry cell offers an easy way to correct the tool’s output for your known weight requirement. Once you have correctly entered your height, weight, rig details and tank, while leaving personal buoyancy blank, you can correct the output of the tool by going back and entering the difference in the personal buoyancy cell. Then, the tool will correctly predict your weight requirement for a new rig, wetsuit or drysuit.

    We have made a few other tweaks, including
    1) automated selection of a Farmer John wetsuit style in the Suit Tab, accounting for the extra flotation contributed by the neoprene overlap;
    2) correction of an obscure error in one formula for buoyancy after bcd failure at depth
    3) correction of the Tanks Tab for the correct specifications of the Faber HP100 tank, and addition of a rare medium pressure tank of similar size, but lower capacity.
    4) addition of a POSITIVE buoyancy cell to the Rig Tab for the additional buoyancy provided by a full face mask, double hose rig or floaty fins.
    5) miscellaneous edits in the Users Manual for clarity
    NOTE: other than the error correction described above, no formula changes were made in this revision.

    Keep in mind that this tool was not intended to be a “weight calculator”, though as it turns out, most divers use it that way. It was designed to evaluate the possibility of self-rescue in a wetsuit or drysuit after catastrophic bcd failure or drysuit flood by partial weight ditching. As @johndiver999 once pointed out, ditching weight at depth in a wetsuit does not automatically result in a runaway ascent. Instead, due to wetsuit compression at depth, you are probably still negative. If you ditch some of your weight, you may be able to fin up. As you do, you will become less negative due to wetsuit re-expansion. At some point below the surface you will become neutral, and can rest and offgas. Only then do you need to confront your final buoyant ascent. And using this tool, you may be able to keep that final positive buoyancy to a minimum, converting a potentially fatal catastrophic failure to a survivable scenario. The User’s Manual discusses this in great detail, and we’re proud to have this tool help your understanding of buoyancy.

    But if you’re not really interested in all that theory, but just want an accurate “weighting predictor” for a new wetsuit or drysuit, attached to this post is the Quick Start section of the manual. In just one page, it’ll get you going without all that “other stuff”.

    Even with all the math, all the corrections, and all the fields for customization, you may still come up with a recommendation at odds with what you really need to dive neutrally. That’s because there’s just no way to account for all the differences in wetsuit design, neoprene deterioration over time, or personal differences in drysuit inflation technique in a single generic tool. But if we can come within a pound or two, we think that’s a success, because you can confront a new equipment configuration or different environmental suit and still come close to your actual weight requirement without trial and error.

    Recent modifications to the formulae make this tool relatively accurate for a wide range of divers. Even in the face of the tool’s potential inaccuracies as a weight predictor, you can still prepare for a catastrophic buoyancy failure by learning how weight ditching (even with a balanced rig) can potentially improve your safety. Similarly, you can learn how “thick wetsuit re-expansion” in the last 15 feet can have a real impact on your diving safety and potential for DCS, unless you are properly weighted, whether by the use of this tool, or traditional buoyancy checks.

    Enjoy! And please keep the suggestions and corrections coming.
    We’ll fix the errors for sure, and maybe implement your “next great idea” too!

    Attached Files:

  8. johndiver999

    johndiver999 Manta Ray

    # of Dives: 500 - 999
    Location: Gainesville FL
    Thanks for the mention. I think the addition of a “personal calibration factor” should be very useful.

    As you explained, the primary benefit of your considerable effort is not to accurately predict how much lead you need, but rather to estimate how much lead you can drop in an emergency in order to optimize the safety of your ascent. This requires a computation of and an appreciation of how significant wetsuit compression can be.

    Based on comments made in other discussions by many members, I think there’s widespread under appreciation of the potential benefit of dropping (some) lead.

    We often hear the following ideas presented as universal truths and represented as if they apply to all situations:

    • If you are weighted properly, there should be little or no air in your bc at depth.
    • There is no foreseeable situation which would point toward the need to drop lead at depth.
    • The ONLY place it make sense to drop lead is at the surface.
    • Dropping of any ballast (lead) at depth will invariably result in an uncontrolled ascent.
    • It is always desirable and beneficial to carry the absolute minimum amount of ballast that is needed to keep you neutral at 15 ft or so (with a nearly empty tank).
    Along these same lines, we often see new divers discussing and being advised to configure all their ballast on a back plate or in some other nonditchable location- even when diving in cold water with a thick wetsuit.

    All these ideas help explain why the popularity of a weight belt seems to be waning.

    It always cracks me up when dm trainees are given advice how to CHANGE their ballast configuration in order to allow them to demonstrate (in a class) a tank removal and replace while underwater, rather than being encouraged to find a permanent solution or a ballasting configuration that will allow performance of the skill during every dive.

    There is a widespread failure to comprehend that the remove and replace skill is not a parlor trick, but rather a useful skill that a diver could call upon to address an entanglement. Wearing some ballast on the body (that is ditchable) and not having it all on the tank in an unditchable configuration has several potential benefits which seem to be unrecognizable to many.

    Hopefully the quantitative results of this tool will help more people to convince themselves about the safest way to optimize ballast for their specific application.
  9. RTC'83

    RTC'83 DIR Practitioner

    # of Dives: 25 - 49
    Location: North Texas
    rsingler likes this.
  10. gr8jab

    gr8jab Manta Ray

    # of Dives: 100 - 199
    Location: Oregon, USA
    Thanks for constantly making improvements! I'm starting by using your new personal buoyancy feature (which is much improved over the last version) to estimate my lead needs. But, I plan to visit the pool and collect some data and then reverse calculate my personal buoyancy.

    Please critique my plan:
    1. Estimate my pool weight needed by making my best guess of everything possible
    2. Find my current lead needs, by fine tuning with lead:
      1. In pool at 15 feet
      2. Tank at 300psi or 500psi (whatever is handy)
      3. Wing empty
      4. Neutral Buoyancy
    3. Find my rig's in-water buoyancy
      1. BP/W w/o padding, I'm assuming it is negative
      2. Use my typical kit (light, knife, radio, etc)
      3. Dangle it in the pool with a string on a scale
      4. Do this after I've already gotten it wet and minimized trapped air
    4. Find my camera's in-water buoyancy
      1. String/scale method
    5. Using the Optimal Buoyancy Computer
      1. Enter all the data I've measured
      2. Enter all my personal data (height,weight)
      3. Modify the 'personal buoyancy' numbers until the QuickResults match my experimental results from step #2 above.
      4. Save my settings!
    6. Make use of the Optimal Buoyancy Computer
      1. Figure out where best to put my lead (rig, belt, pockets)
      2. When something changes, recalculate to guesstimate new weight
        1. Different tanks
        2. Different salinity
        3. Different exposure protection
        4. w/o camera/pony
    Doctor Rig and John C. Ratliff like this.

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