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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[tridacna]

Is there an option to account for water salinity? For example the one of the Atlantic Ocean vs Red Sea is very different, with very different impact on buoyancy.

The variability in salinity from the Red Sea to the Atlantic Ocean (in diveable locations) has minimal effect on buoyancy. There is absolutely no reason to account for this on the spreadsheet. In reality, you will have to travel with a calibrated refractometer to accurately measure dissolved salt. How do I know? I'm a saltwater aquarist and do exactly that. I measure salinity at every dive site now mostly to dispel this silly myth. I have yet to discover a dive locale where salinity has any impact on diving. Between 34-36 ppt almost everywhere.

I used to dive at Blue Water in Bermuda and the boat captain used to tell divers to add an additional 10% of lead to their belts to account for the "increased salinity" there. My refractomer showed 34 ppt - on the low side. In reality, they were sick of divers not taking enough weight and wanted to make sure that they would sink. Good tactic but BS nonetheless.

 

[David Novo]

The variability in salinity from the Red Sea to the Atlantic Ocean (in diveable locations) has minimal effect on buoyancy. There is absolutely no reason to account for this on the spreadsheet. In reality, you will have to travel with a calibrated refractometer to accurately measure dissolved salt. How do I know? I'm a saltwater aquarist and do exactly that. I measure salinity at every dive site now mostly to dispel this silly myth. I have yet to discover a dive locale where salinity has any impact on diving. Between 34-36 ppt almost everywhere.

I used to dive at Blue Water in Bermuda and the boat captain used to tell divers to add an additional 10% of lead to their belts to account for the "increased salinity" there. My refractomer showed 34 ppt - on the low side. In reality, they were sick of divers not taking enough weight and wanted to make sure that they would sink. Good tactic but BS nonetheless.

North Red Sea is around 41 ppt vs. 33-37 ppt in the Atlantic Ocean. I just read on a different post that this difference could be relevant. Is it not?

 

[tridacna]

North Red Sea is around 41 ppt vs. 33-37 ppt in the Atlantic Ocean. I just read on a different post that this difference could be relevant. Is it not?

Completely irrelevant. Refractometers are temp dependent. I measure at 77F. Even if true, a difference of 4ppt is going to make no difference at at. Remember that the difference from 0-36ppt is 10%. So 4ppt would be less than 1% in added weight. Good luck adding 1% to account for the salinity swing. Not worth it.

 

[rsingler]

Well, for the geeks that use the Optimal Buoyancy Tool, that 1% could be an extra kg of carried lead. 36 to 41ppt is probably even less than 1% depending upon temperature. So, everybody's right.

It's not significant.
It is measurable.
And, if we put in salinity as a user adjustable variable in the tool, we could predict that half pound in advance.

We'll see if there are more users who want to define their salt water.
The default salinity in the tool is 1.027 kg/l, which corresponds to a salinity of about 36ppt at 20°C

 

[Steve_C]

[QUOTE="rsingler, post: 8910171, member: could be an extra kg of carried lead.

we could predict that half pound in advance.
[/QUOTE]

kg is 2.2 lb not 0.5 lb. Divided wrong.

 

[rsingler]

Thanks, but what I was trying to say was that 1% is a max of 1 kg or 2.2 lb.
But by my calcs, going from a salinity of 36 to 41ppt ends up being more like a half pound. Much less than 1%. Which is why @tridacna has a good point. But for those who are interested enough in the theory and numbers to really zero in, we can make the tool that precise.

It's a theory exercise, really.
And a pride thing, that a diver who has his weight dialed in in one setup, can use theory and calcs to let him jump in different water, in a different suit, with different tanks, and nail his buoyancy on the first try.
But really, it's just a fun mental exercise for those that like that sort of thing.

 

[tridacna]

Rob - my point is that it is nigh impossible to know what the accurate salinity is at any dive site if you don't measure it at that particular moment in time. You cannot rely on a historical measurement to know that number. All your other variables are reliably and easily measured. This one is not and has less than 1% of weight differential on the outcome. Remember that if it's more, the water temp has to be much lower making measurement even harder. There is also a difference between refractometers that measure salt brine (usually set for 59F) and those for coral reefs that measure ionic content of seawater. There have been insignificant differences between dive sites in Cape Town, South Africa, Bermuda in the Atlantic and Eilat in the Red Sea. A spurious variable indeed.

 

[rsingler]

Thanks, @tridacna !
Good counsel.

The Optimal Buoyancy Computer.
"A tool for measuring with a laser, marking with a Sharpie, and cutting with an axe."
(to paraphrase an oft-quoted reminder)

Now that we're up to page 10 in this thread, it probably bears repeating (as @johndiver999 has before me) that this tool was NOT designed to be a weight calculator. From its origins almost two years ago, it was presented as a way to assess methods of self-rescue after a catastrophic equipment failure. It showed mathematically that jettisoning some weight does NOT automatically result in a runaway ascent, even for a "balanced rig." Instead, due to wetsuit compression, a diver with a bcd failure or a drysuit diver with a suit failure goes from VERY negative to somewhat negative, and may be able to swim up. At some point closer to the surface, the diver becomes neutrally buoyant due to expansion of retained bubbles or neoprene re-expansion, and can offgas and rest. Only at that point does the diver become positively buoyant, and the tool shows how to compute in advance an amount of weight to ditch so that the shift to positive buoyancy from the neutral point to the surface is controllable. This tool is intended as a self-rescue educational tool, though it functions well as a weight calculator IF you are meticulous about inputting your variables.

Perhaps look at the video and review this post in an earlier iteration of this subject:
Buoyancy, Balanced Rigs, Failures and Ditching – a comprehensive tool

Enjoy!

 

[rsingler]

Thanks to the vigilance of @SJT1961, we have corrected yet another small formula error.
The Balanced Rig sheet was returning an erroneous Personal Buoyancy for Fresh Water.
I'm pleased that this continues to be a crowd-sourced project, and I truly appreciate all of you who have sent in suggestions and corrections over the past 2+ years. We're now up to over 1,000 downloads, and I apologize to those of you who now have to download the corrected version.

Thank you, @SJT1961!

 

[rsingler]

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.