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Optimal Buoyancy Computer

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

  1. gr8jab

    gr8jab Manta Ray

    # of Dives: 100 - 199
    Location: Oregon, USA
    628
    371
    63
    Hello all! I made it to the pool today, and here is the data I collected and my feedback.

    POOL TIME

    Setup:
    me: 5'10" at 230lbs
    swimsuit
    short sleeve rash guard
    3mm booties
    HOG aluminum backplate
    HOG 35lb wing
    2 small ditchable weight pockets on harness
    4 small non ditchable trim pockets on backplate
    Original Nautilus Lifeline
    Deep 6 fins
    80CF Al rental tank​

    Personal buoyancy. It was really hard to estimate 1/3 full lungs. I think this is where some of my sources of error might be in this process, but I'm hard pressed to find a different method. I found that I was able to stay at eye level with no weight or lift at what I think was 1/3 full lungs. I was wearing a swim suit and short sleeve rash guard, and mask/snorkel, nothing else.

    The pool had a max depth of 9', which is probably another source of error, since at that depth there are a lot of changes in buoyancy in short distances. I wish I was able to test in 15' of water instead. Wearing my setup as described above and with 2850psi, with NO ADDITIONAL weight, I was able to sink with a full exhale and gently descend. While at the bottom of the 9' pool (where I tried to hover just off the bottom, so I'm calling it 8') I couldn't take a shallow breath without going positive. I added 2 lbs and felt very comfortable, able to ascend and descend at will, within my normal breathing range. I think 1 - 1.5 lbs would have been right on the nose perfect. I spent considerable time getting all the air out of my rig, both from the bladder and general trapped air.

    Later, after the dive, I hung my rig in the water via a luggage scale. My son was in the water and took more time twisting and turning the rig to get out all the trapped air. It measured 2.4 lbs (sinking).

    SPREADSHEET TIME

    I plugged my numbers into the spreadsheet, including the 2lbs of ditchable weight. It said I was -6.2 buoyant at 8' depth. But, I'm pretty sure I was around neutral. I'm not sure if I'm looking at the right numbers. Please check me. Please note that it is very possible that I would not have added those 2lbs if I had 15' of pool depth to experiment. These shallow depths of my pool are probably the most error prone for the spreadsheet.

    The Quick Results did recommend only 0.3 pounds of weight. That is less than 2lbs from what was probably optimal, so I think that was a good estimate.

    I have attached my spreadsheet with my numbers for everyone to check.

    CONCLUSION

    I plan to keep these numbers and use the Quick Results page to estimate my weight for my Florida trip in November. I will use my experiences at deeper depths in November to fine-tune my personal buoyancy number, and will then use the spreadsheet for future trips with different wetsuits!

    I hope to add my camera and flashlight buoyancy soon, as that might offset some of the weight I'll need in salt water.
     

    Attached Files:

    Doctor Rig and chillyinCanada like this.
  2. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    3,312
    3,669
    113
    Than you so much for contributing your data! This will really help as we fine tune the program. I'll look at your numbers and get back you you by PM.
     
    Doctor Rig likes this.
  3. Snodge

    Snodge Angel Fish

    # of Dives: 100 - 199
    Location: BC
    14
    6
    3
    check cell E18 on "drysuit" tab seems it should be "=e15+E16"
     
  4. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    3,312
    3,669
    113
    Will do, thanks!
     
    Doctor Rig likes this.
  5. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    3,312
    3,669
    113
    @Snodge , thank you for your detective work! This is truly a joint project.

    Your pickup is correct. There's an error in cell E17 in the Drysuit tab.
    It has been corrected.
    Spreadsheets v68 have been loaded in Post #1.
    Thank you, @Snodge !
     
    Doctor Rig likes this.
  6. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    3,312
    3,669
    113
    Looked at your numbers, and while I haven't finished, they revealed another spreadsheet error, in the Lift Tab. Right now, it looks like a 2.2# error that puts the results much more in line with what you found experimentally.

    Readers: note that Lift tab cells B10:F10 have an incorrect formula for Fresh water only.

    I will continue going through @gr8jab 's data, and load new spreadsheets as soon as I finish looking for errors based upon what he found.
    Thank you @gr8jab !
    More to follow.
     
    Doctor Rig likes this.
  7. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    3,312
    3,669
    113
    Thanks to @gr8jab , we have been able to discover and correct two more small errors in the spreadsheet.
    Formula errors were corrected in Lift tab B10 thru F10, and in four similar hidden cells.
    The errors only affected fresh water divers, and did not account for personal buoyancy in those cases.
    Versions 69 have been uploaded into Post #1.

    Thank you again to our community!
    Bit by bit, we'll perfect this!
     
    couv and FreeFlyFreak like this.
  8. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    3,312
    3,669
    113
    For those of you who are inclined to follow @gr8jab 's lead and really test out the predictions...

    Okay, I'll start over. For the ONE GUY who's inclined to do this too :wink:, here's an answer to one of @gr8jab 's conundrums: "estimating 1/3 full lungs". From reading the manual, you know that much is dependent upon the change in buoyancy between full and empty lungs. Indeed, experienced open circuit divers use that very fact to glide up and over coral heads as they explore, because of the significant (>6lb!!) buoyancy change between full and empty lungs. By inhaling and exhaling, they can instantly change their buoyancy without messing with their bcd.

    In order to standardize measurements, we calibrated the formulas for "end-exhalation". For those who aren't familiar with the respiratory volume diagrams, it isn't clear whether that "means breathe out everything you can" or something else. As a result, in the manual we described it as 1/3 full lungs. Close enough for government work. But for an intense numbers guy like @gr8jab , that meant trying to figure out how much was 1/3 full.

    What we meant in using that term was: breathe in naturally, then breathe out. At the point where you stop a natural, relaxed exhalation, you're at "1/3 full". Now move on in the test. Many of you will recognize that you've still got volume left to blow out, in case you were inflating balloons for your daughter's birthday party, but that's not what we meant.

    Hope this helps as you measure your Personal Buoyancy in a pool.

    Why do all this in the first place? Especially when you can just do a buoyancy check in the ocean before you drop!
    Well, part of the value of this tool, wholly apart from calculating how much weight you might ditch for self-rescue, is having an easy way to shift gears when you buy new wetsuit, or when you shift from your usual Great Lakes steel tanks to Caribbean aluminum rentals, or when you want to start using a completely different setup and would like to arrive for your first dive a bit more prepared. Barring signifcant personal weight change, one personal buoyancy check will last through lots of rig changes.

    Dive Safe!
     
    couv and FreeFlyFreak like this.
  9. FreeFlyFreak

    FreeFlyFreak Solo Diver

    # of Dives: 25 - 49
    Location: California
    294
    221
    43
    Line 17 of the wetsuit tab "change depth here" does not work correctly. Should be able to just type in a number, instead it brings a drop menu "full farmer shorty"
    Worked fine in version 57
     
  10. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    3,312
    3,669
    113
    Thanks! I'll check it out soon!
     

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