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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[RTC'83]

Thanks for sharing, amazing tool!

 

[David Novo]

After doing some calculations for drysuit with single 15l steel tank or twins of the former, it always results in a 40 lbs lift being enough (after ditching some weight in either a wing failure or drysuit flood scenario). Does this make sense (same lift for single or twins, not same wing)?

 

[Mike1967]

Does this make sense

As long as you're not over weighted, it does.

 

[David Novo]

As long as you're not over weighted, it does.

Yet I see a significantly number of posts claiming that 30 lbs is enough for cold water diving. How?

 

[rsingler]

I'm guessing that those that claim that are depending much more on reserve suit buoyancy, or partial air trapping in a wing failure. The spreadsheet is fairly conservative in its estimate of reserve drysuit lift. It's likely that from experience, some folks use that lift without thinking about it.
And in the case of suit flooding or a wing tear, it should be easily possible to trap 10# of lift in a leg or other intact suit area. It's less true, but still possible with a wing, also. The tool presupposes total loss of lift, as noted in the manual.
It's all a question of how close to the limit you want to be. The Lift page should map that out, so you can see the instances in which you'd be -10# or more and having to depend on imaginative redundant lift.

 

[David Novo]

I'm guessing that those that claim that are depending much more on reserve suit buoyancy, or partial air trapping in a wing failure. The spreadsheet is fairly conservative in its estimate of reserve drysuit lift. It's likely that from experience, some folks use that lift without thinking about it.
And in the case of suit flooding or a wing tear, it should be easily possible to trap 10# of lift in a leg or other intact suit area. Lows true, but possible with a wing. The tool presupposes total loss of lift, as noted in the manual.
It's all a question of how close to the limit you want to be. The Lift page should map that out, so you can see the instances in which you'd be -10# or more and having to depend on imaginative redundant lift.

Thank you for the clear explanation.

 

[rsingler]

It's not as though a possible drysuit lift formula error inside the spreadsheet could be a factor in this particular issue. Once you remove drysuit lift from the equation (whether or not it was calculated correctly) then residual lift is pretty easy to determine. There's a little bit from some neoprene pieces (hood and gloves) that may be compressed at depth. There is your stated wing lift from the manufacturer. And that's about it. It's enough to offset your tanks, bands and backplate, or it's not.

 

[David Novo]

It's not as though there could be a calculation error inside the spreadsheet, regarding this particular issue. Once you remove drysuit lift from the equation (whether or not it was calculated correctly) then residual lift is pretty easy to determine. There's a little bit from some neoprene pieces (hood and gloves) that may be compressed at depth. There is your wing. And that's about it. It's enough to offset your tanks, bands and backplate, or it's not.

That is true, but according to the spreadsheet, if you dive with the majority of the lead on a weight belt, you can get away with a 30lbs wing, without relying on trapped gas.

 

[rsingler]

That is true, but according to the spreadsheet, if you dive with the majority of the lead on a weight belt, you can get away with a 30lbs wing, without relying on trapped gas.

That change in required weight is due to a separate issue.
You only need 30lb of lift total, for the setup you have entered. That includes baseline drysuit lift, (which will float your weight belt and you, out of your rig).
However, your rig apparently will not float itself with all your weight in the backplate, with a 30# wing.
By transferring some weight to a weight belt from the rig, your rig will float itself on the surface if you have to shed it, and the wing lift now just reflects what is required to float your entire setup, rather than extra lift required to float the rig when you don't have your drysuit helping.

 

[HKGuns]

@rsingler I sense something is wrong in V.58.....I have been using V.57 and the results are quite different.

The difference in my case seems to be V.58 says my Faber FX80 "Sum of Tank Buoyancy" is -1.7 whereas V.57 has it at -7.2.....Not sure which is correct, but it seems too large a difference. The resulting end values for weights to add are V.58 16 pounds vs. V.57 11 pounds. Thinking a 5 pound difference, all else being equal, version to version is too much.

Just trying to help, not criticize. I went over everything several times to ensure my values were correct on both sheets.