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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[anchochile]

The largest source of error, as noted above, is in estimating your wetsuit/drysuit buoyancy.
I would suggest actually measuring your neoprene (fold an area away from a seam, measure and divide by two).
I realized I was overestimating by following the manufacturer stated thickness.
Also consider how you fly your drysuit. It sounds like you run it a bit emptier than the spreadsheet assumes for the thickness of your liner.

Ok, I measured all my neoprene - either thickness, for the suits, or directly with lead in the bathtub where possible. This chart captures my measurements and the resulting buoyancy assumptions (in blue) that I am using in the spreadsheet:

I used these inputs to run a few scenarios where I know my weight requirement. You can see the spreadsheet's suggested lead compared to my actual lead used in the blue columns:

As you can see, the results are now closer to reality, but still 3-5 lbs more than I actually need (potentially more - it's possible my steel bp leaves me a bit overweighted in the scenarios where I use no lead).

At this point, should I start tweaking the inputs (e.g. suit buoyancy or personal buoyancy) until it reflects my real-life experience, and then use that as my new baseline buoyancy to run other scenarios?

And yeah, I'm probably overthinking this tool which is just theoretical - but I enjoy nerdy stuff like this, and it's especially helpful to think about the safety of diving these setups without ditchable weight in warm water.

 

[rsingler]

When transferring those numbers to the spreadsheet, is any fresh>salt adjustment needed since I'll be measuring in fresh water?

No. The volume of sea water they displace is not large enough for the 2.4% difference to mean anything.

 

[rsingler]

I can never find it

It's a sticky in the Advanced Forum. Usually one of the top three posts.

 

[rsingler]

At this point, should I start tweaking the inputs (e.g. suit buoyancy or personal buoyancy) until it reflects my real-life experience, and then use that as my new baseline buoyancy to run other scenarios?

Exactly. Personal buoyancy would be my first adjustment. Glad you're having fun!
Though few folks know it now, the spreadsheet was originally intended not as a weighting calculator, but as a tool to demonstrate self rescue by partial weight ditching. It evolved in response to the "if I dump weight I'm going to rocket to the surface and die!" comments that pop up from time to time.
As you can prove to yourself, due to wetsuit compression, if you drop some weight, you may still be negative due to wetsuit compression, but not so negative that you can't swim up to a point of neutral buoyancy and rest before continuing with a buoyant ascent. The time spent offgassing while neutral (at, say, 15-40ft) will reduce the likelihood of DCS, and turn an otherwise fatal bcd failure into a survivable scenario.

 

[mtoyama]

Hello, I recently started using this and I converted it to Google Sheets in .xlsx mode. Can I still trust it? Seems to be working fine.

See: OptimalBuoyancy_v71.xlsx

 

[rsingler]

Yes, the formulae transfer okay, but the protective formatting does not. You may see data that's normally hidden because the results won't make sense in the context for which they're hidden.

 

[vinsanity]

Hello, I recently started using this and I converted it to Google Sheets in .xlsx mode. Can I still trust it? Seems to be working fine.

See: OptimalBuoyancy_v71.xlsx

Biggest warning is to beware that rsingler used cells to the right and below the main cells you interact with. They have white text color so you don't see/get distracted by them, but if you click them, you will see they have formulas in the formula bar. Don't accidentally delete or overwrite those cells when the protective formatting is lost during import.

I started taking my own notes off to the side and almost overwrote some important intermediate values.

@rsingler Great work BTW. Not only is the tool convenient for calculations, but I learned a lot by just tinkering with the numbers as well as the concerns that the tool brings up for you to think about!!! Thank you so much!

 

[The Cosmicist]

Thank you @rsingler and others who've worked very hard on this over two years. I just "discovered" this and am chomping at the bit to work through it. I have a question, though, and forgive me because I didn't quite understand after reading through the thread.

I know that with my current 5mm wetsuit and 6.5mm booties in a salt water pool (salt water pools have low salinity... small wrench thrown?) I need 12 lbs. of weight to start sinking after full exhalation, maybe a tiny bit less to sort of hover right at the surface. How can I incorporate this into the calculator and work from there? Or do I really need to start from scratch, measuring myself and my wetsuit separately? I know my body is negatively buoyant, always has been, I just don't know exactly how much. I'd rather just use the known number with me and the wetsuit, if possible.

Thank you!

 

[James79]

Thank you @rsingler and others who've worked very hard on this over two years. I just "discovered" this and am chomping at the bit to work through it. I have a question, though, and forgive me because I didn't quite understand after reading through the thread.

I know that with my current 5mm wetsuit and 6.5mm booties in a salt water pool (salt water pools have low salinity... small wrench thrown?) I need 12 lbs. of weight to start sinking after full exhalation, maybe a tiny bit less to sort of hover right at the surface. How can I incorporate this into the calculator and work from there? Or do I really need to start from scratch, measuring myself and my wetsuit separately? I know my body is negatively buoyant, always has been, I just don't know exactly how much. I'd rather just use the known number with me and the wetsuit, if possible.

Thank you!

I got pretty close by working the problem backwards.... my pool is salt, but as you said they are really low salt, so I used the freshwater calculator. Then plug in your suit and boots, and zero the weight of rig/reg/everything else. Plug in a rough guess in personal buoyancy (or start it at zero). Then see what it says for lead needed. If it doesn't match your actual need, adjust personal buoyancy until it does. Then use that number as a baseline for equipment changes. Accuracy of this method is limited by how well your wetsuit matches the spreadsheet's data... but it get's me awful close.

Respectfully,

James

 

[The Cosmicist]

Thanks! I will try that this evening.