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.

---

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.

---

 

[Open Ocean Diver]

Well, shoot, guys! @SJT1961 points out that my revised spreadsheet was an incomplete correction of the small formula error on the Balanced Rig page.
Just attached a second revision of that. We should be good now.
Keep your eyes on me. Too many formulas buried in this thing, lol!
My apologies to those of you who downloaded the revision right away.
Thanks, @SJT1961!

Version 71 is the current copy.

Assuming the manual hasn’t changed from ver31?

 

[rsingler]

Assuming the manual hasn’t changed from ver31?

Correct. All the tinkering is behind the scenes. No changes to how things are presented after the last major revision.

 

[Open Ocean Diver]

Correct. All the tinkering is behind the scenes. No changes to how things are presented after the last major revision.

Thanks

You should create an app that can be used in the field.

 

[TuckerIdaho]

Any tips on calculating BCD buoyancy to compensate for backplate weight? (6lb XR plate)
I'd like to get the Rig sheet closer to "my" reality.

 

[rsingler]

If you can't hang from a luggage scale in a swimming pool with all the air out of the bcd, then estimating works pretty well.
The BP weight of 6# should be corrected for its displaced water density, which in the case of a thin backplate is usually less than half a pound. But once you add the buckles and D-rings, it comes right back to 6#. The bcd itself is usually neutral, unless you have foam padding. Open cell foam is buoyant at the beginning of a dive, but neutral when it gets saturated. If you have closed cell padding, then estimate its volume, and subtract 1lb for each 5" x 5" x 1" (25 sq in) amount.
If you have a LOT of extra hardware, weigh that and add it to the 6# plate.

This is a long way of saying, probably just put -6# in the BP/bcd weight field.

 

[TuckerIdaho]

Thanks! It just dawned on me that I can do that with a digital fish scale on the dock around the corner from here. hah. Only catch is its saltwater instead of a pool.

 

[rsingler]

FW to SW is a 4% difference. -6# vs -5.76#
In other words, insignificant for gear displacement.
Perhaps 4lb difference for a human's volume displacement.

But spend some effort getting all the air out of the bcd and pockets.

 

[johndiver999]

FW to SW is a 4% difference. -6# vs -5.76#
In other words, insignificant for gear displacement.
Perhaps 4lb difference for a human's volume displacement.

But spend some effort getting all the air out of the bcd and pockets.

Density of seawater is 1.024 ???

density of seawater - Google Search

 

[tridacna]

Density of seawater is 1.024 ???

density of seawater - Google Search

Average density of sea water is about 1.025kg/l. Or g/cm3 if that floats your boat. Sorry - could not resist.

1.024 is close enough for government work. What's the issue? I hate using density anyway. Prefer to use salinity measurements.

 

[johndiver999]

Average density of sea water is about 1.025kg/l. Or g/cm3 if that floats your boat. Sorry - could not resist.

1.024 is close enough for government work. What's the issue? I hate using density anyway. Prefer to use salinity measurements.

Salinity percentage is not identical to density differential. I should have said specific gravity - to be more correct. The issue is the reference to 4%