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]

PM sent

 

[Turtle Friend]

Hi Scubaboard,

I (186 cm, 86 kg) calculated a couple of scenarios according to my current (warm, salt water diving in 3/5mm and -0.9 kg aluminium BP/W, -1.8kg first stage, currently 3 kg of lead) and my future dives (cold, fresh water diving in drysuit with -1.5kg canister light, -1.8kg first stage and steel -2.7 kg BP/W). Seems like I need for the warm, salt water dives 30lb/14kg and for cold, fresh water dives 40lb/18kg. However, after reading some threads I didnt find any answer to my newbie-question: Why shall I simply not choose a Wing with a very high Wing lift (40 lb) to be prepared for any of the 2 above scenario? That I have a wing with a high lift capacity does not mean that I will use all the capacity whenever I don't need it (e.g. warm, salt water diving in 3 or 5mm). Right?

Additionally I need to fine tune my personal buoyancy: Thus, I would like to know whether I can do the personal buoyancy test in chlorinated water (like a swimming pool) and mark that in the sheet as fresh water or will that difference (fresh vs. chlorinated water) affect the results significantly?

Thanks for answerring my question

 

[stepfen]

Hello and welcome.

Why shall I simply not choose a Wing with a very high Wing lift (40 lb) to be prepared for any of the 2 above scenario? That I have a wing with a high lift capacity does not mean that I will use all the capacity whenever I don't need it (e.g. warm, salt water diving in 3 or 5mm). Right?

The problem with having a wing with "very high lift capacity" as you call it is that high lift comes with the price of more wing material hence more bulk and more drag in the water (even when the wing is empty). That being said I wouldn't call a 40lb wing "very high lift capacity". My figures are somewhat similar with yours (I am close to 105kg and 190cm and BTW you don't mention anything about what tanks you dive - tanks can make a huge difference, I use 15lt steel tanks) and I dive with a 17lt wings (which should be close to 40lb - sorry I live in the metric world). 15lt wings are usually considered "standard" here and when you put them side by side with mine you can hardly notice any difference in terms of dimensions. There are wings, used for example for big double tanks, that have lift of close to 22lt/60lb or more. That's what I would call "very high lift" and if you don't need such lift you should stay away from them.

In your case I would get a 17kg wing to cover both summer and winter. If you have the $$ you could buy 2 wings (and maybe a second heavier steel plate for winter - just saying ) but that's up to you to decide.
BTW try to spend a lot of time with the tool to make sure you are using it correctly, with correct numbers and that you haven't missed any details. Small changes or mistakes can make quite a difference in the results. Also after you get the results you should try to verify them in the water. Differences of +/- a couple of kg can occur.

Additionally I need to fine tune my personal buoyancy: Thus, I would like to know whether I can do the personal buoyancy test in chlorinated water (like a swimming pool) and mark that in the sheet as fresh water or will that difference (fresh vs. chlorinated water) affect the results significantly?

The difference between chlorinated and really fresh water should be negligible. Remember all these are approximations anyway.

All the best

 

[Turtle Friend]

BTW you don't mention anything about what tanks you dive - tanks can make a huge difference, I use 15lt steel tanks)

Thanks for your answer. My categorization that 40 lb lift capacity was very high was due to the fact that I have never dived doubles so far (but want in future/will) and in this case I understand that 40 lbs is at the higher end of single tank lift capacity (at least what I can find on manufacturers websites like Halcyon for single tank wings).
Currently I don't have my own tanks so I mostly dive rented Generic AL80 (first row in the calculator).

In your case I would get a 17kg wing to cover both summer and winter. If you have the $$ you could buy 2 wings (and maybe a second heavier steel plate for winter - just saying ) but that's up to you to decide.

I was thinking to get a 40 lb (18kg) wing and a steel backplate (2.7 kg) and a 30 lb (14 kg) wing an aluminium backplate (0.9 kg). I hope that would be fine.

 

[Jcp2]

Maybe that’s a high lift figure for a wing, but most divers use a jacket, and that amount of lift is fairly typical.

 

[Sbiriguda]

Awesome thread , thanks

 

[jnocerin]

First off this tool and all of the updates made through diver input is fantastic. So I am a relatively new diver, not by years, but by number of dives (currently I have 12 dives). I am preparing to start diving more regularly since moving to NorCal, and just got an aqualung semi dry solafx 7/8mm How would I correctly account for that I. The wetsuit tab as it seems to be more buoyant on the surface, and I am fully floaty with just the suit. For reference I am 5”8”, 220.
I plan to figure out my buoyancy in my pool soon, but it currently too cold (unheated) to determine my base personal buoyancy, although I know I can easily stay on the surface taking normal breaths on my back, so I assumed “neutral” 0 in the spreadsheet for now.
Thanks in advance, and excuse the Newbie level of the question.

 

[rsingler]

No worries!
I dive the exact same wetsuit here in NorCal. Great neoprene!
I enter as wetsuit, 7.5mm, New_Soft
to account for the average between the chest and leg thicknesses.

As for your personal buoyancy, from what you describe in a presumably freshwater pool, I might be tempted to put in +4# for salt water rather than zero, but that's only a WAG.

Feel free to open a conversation with me as you work the tool. Thanks for joining the discussion!

 

[David Novo]

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.

 

[rsingler]

At this time, there is not. The default value is an average salinity, which apart from the Red Sea, won't mean more than a 1.5 lb inaccuracy.

If you're interested, PM me and I'll tell you how to enter the exact value inside the tool for the salinity you wish to use.

If there's enough interest, we can certainly add that as an option.