Info Optimal Buoyancy Computer

The Optimal Buoyancy Computer
A tool to help nail buoyancy and improve safety, before you splash​

1) How much lead should I carry with my new wetsuit?
2) How big a wing should I buy?
3) Will my BCD support my lead, both at the surface and when my wetsuit is compressed at depth?
4) Will my BCD support my rig without the help of my wetsuit/drysuit, if I doff it at the surface in an emergency, or underwater due to an entanglement?
5) How do I balance my rig?
6) How might partial weight ditching help me deal with an emergency? Will it really result in a runaway ascent?
7) How does the neutral buoyancy check change with thick neoprene?

I’m excited to announce the release of the Optimal Buoyancy Computer.
Designed to answer a variety of buoyancy questions, it provides accuracy directly proportional to the precision of your data input. Starting with as little as your height, weight and suit thickness, you can get ballpark weight requirements quickly. With additional information, you can compare equipment configurations, and plan for self-rescue after hypothetical equipment failures.

This tool is an Excel spreadsheet, and is a revision of a tool originally released in Buoyancy, Balanced Rigs, Failures and Ditching – a comprehensive tool , which was itself a revision of a toy spreadsheet first introduced in this thread: Advice on lift capacity for BP&W in April, 2018. After months of user suggestions, this new tool uses a simpler, modified data input system, and produces both simple and complex analyses of buoyancy. It works in both metric and Imperial units, salt and fresh water, and with both U.S. and European tanks.

Included is a 50-page user’s manual to lead you through the more complex parts of the tool, and a Quick Start section to get you going with minimal familiarity with spreadsheets. Additionally, the manual discusses the theory behind the more complex buoyancy calculations, whether you need help with Excel or not. If you are not facile with Microsoft Excel, the manual will take you through it all, step by step.
Here's the Table of Contents:

Download the .xlsx file for current versions of Excel. Use the .xls file for Excel 97-2003. Other spreadsheet programs may or may not recognize the internal links, but trial versions of Excel are available for free. You will see a generic Excel warning about possible viruses - don't worry, there are none! Click "Enable Editing", and save a copy. After saving, you will be able to edit the data fields for your use.

Many thanks to @stepfen , @johndiver999 , @kmarks , @Akimbo and the many others who have made suggestions and comments along the way.

NOTE: If you are using Excel 2003 and download the .xls file, extensive protective formatting is not functional. Thus, when you are diving a wetsuit (for example), you may be able to see drysuit "data" on the same page. The data for the "other" suit is NOT accurate under those conditions and should be ignored. With current versions of Excel, this information is blanked out for safety.

As each new version is uploaded, the count of downloads returns to zero. We are currently at over 2000 downloads of the tool, counting repeat customers! Thank you for your interest!

WARNING: These spreadsheets are experimental tools using formulas created by amateur divers for educational use only. Numerous assumptions regarding buoyancy have been made based upon only partially tested equipment configurations. The information herein is for your personal educational use and should not be relied upon to determine the adequacy of a given equipment configuration. Consultation with a dive professional regarding equipment, weighting and performing a neutral buoyancy check should all be strongly considered before diving a new equipment configuration. Note specifically that the practice of ditching weight at depth is a controversial one, and the theoretical data in this spreadsheet should not be considered a recommendation of that practice.

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Selected for the ScubaBoard Knowledge Base.

This thread was selected for the ScubaBoard Knowledge Base on 22 November 2021. Special rules discouraging off-topic and counterproductive replies apply after this date.

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[rsingler]

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.

 

[Snodge]

check cell E18 on "drysuit" tab seems it should be "=e15+E16"

 

[rsingler]

check cell E18 on "drysuit" tab seems it should be "=e15+E16"

Will do, thanks!

 

[rsingler]

@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 !

 

[rsingler]

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.

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.

 

[rsingler]

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!

 

[rsingler]

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 , 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!

 

[FreeFlyFreak]

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

 

[rsingler]

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

Thanks! I'll check it out soon!

 

[FreeFlyFreak]

Thanks! I'll check it out soon!

Not sure how it works for anyone else but the suit buoyancy seems way off for me.

To get the calculator to come up with the amount of weight I actually use diving cold I have to enter 6mm full only, nothing else that I wear, everything is close to new. That gives 10lbs of lead, with my tank, SS plate and 1st stage. 10lbs is what I use.


I actually wear 8/6/5 full with a 7/5 hooded vest, plus 5mm boots and 3mm gloves. If I enter that, it gives 23lbs needed! 13 lbs more lead than I actually use.