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.

---

 

[inquis]

As part of the Rig tab. Stainless steel buoyancy in water is 0.87*dry weight. Use a luggage or kitchen scale. Make sure the value is entered with a negative sign in the spreadsheet.

 

[rsingler]

How would you incorporate a 3 mm stainless steel backplate into the calculator?

Hang it in a pool on a luggage scale.
The weight of the SS hanging in air will be slightly greater than in the water, due to the lesser weight of the water that is being displaced by that volume.

OR, weigh the thing and (guessing that its volume is what, 50cc?) subtract 50g from the total.

But now you're measuring with a laser, marking with a Sharpie and cutting with an axe.

Just weigh it and add that to your non-ditchable weight. The mfr probably even lists the weight as a selling point. For a backplate, the water displacement is insignificant.

It goes here in the Rig tab as a negative number.

Lol! @inquisit beat me to it! I didn't read past your post. His answer is the precise one.

 

[azstinger11]

Hang it in a pool on a luggage scale.
The weight of the SS hanging in air will be slightly greater than in the water, due to the lesser weight of the water that is being displaced by that volume.

OR, weigh the thing and (guessing that its volume is what, 50cc?) subtract 50g from the total.

But now you're measuring with a laser, marking with a Sharpie and cutting with an axe.

Just weigh it and add that to your non-ditchable weight. The mfr probably even lists the weight as a selling point. For a backplate, the water displacement is insignificant.

It goes here in the Rig tab as a negative number.
View attachment 782778

Lol! @inquisit beat me to it! I didn't read past your post. His answer is the precise one.

I keep meaning to code this up (giving all due credit to you as the author of course) as a website as a side project and way for me to learn a new tech stack. This was a good reminder.... to add it to my to-do stack lol

 

[Calatinus]

Great, thanks guys! I just discovered I'm overweight most of the time lmao.

Just to be sure, I'm using 2 Aqualung Leg3nd first stages, would that account for 2 x (-0.747) kg first stage weight?

Would there be any "Other fixed buoyancy" using a mono with long hose config (210 cm miflex) and Apeks RK3 HDs?

Such a shame not all manufacturers of scuba gear mention the inherent buoyancy of their products in the manual/datasheet.

 

[rsingler]

Would there be any "Other fixed buoyancy"

Can't quite discern your rig, but if doubles, also need to add for the manifold bar.
Not buoyancy, but weight.
Buoyancy is only floaty stuff like positive fins or double hose hoses.

 

[inquis]

Regarding band & manifold buoyancies, my doubles were already assembled. To get the band+manifold value, I measured it all in the pool, subtracted off the cylinder buoyancy, and entered that in the sheet. When the spreadsheet adds the cylinders back on, the result is the direct measurement. (If your tanks are not empty, subtract off the gas mass as well.)

 

[mattfish]

This is pretty cool! I'm surprised I hadn't come across it before, but I'm glad I have it now.

Is there any issue if I convert this into a script that you can run and answer questions rather than filling in a spreadsheet?

 

[rsingler]

This is pretty cool! I'm surprised I hadn't come across it before, but I'm glad I have it now.

Is there any issue if I convert this into a script that you can run and answer questions rather than filling in a spreadsheet?

No problem.
No copyright. No guarantees.

 

[Sumo888]

Just want to shoutout this resource is awesome!
Taking a lot of the guess work out.

 

[arendvw]

Insipred by this spreadsheet, I've developed this into a webapp, which is available here:

Scuba buoyancy calculator

There are a few philosophical differences:

• Personal weight: I've added a simplified model based on estimated lung capacity, and estimated body fat %. Input: Weight, height, sex and age. This should be able to give a reasonable, but should you feel the need, you can still either do a body fat estimation/calculation.
• Diving suits are estimated in a pretty similar way, but have a bit of an easier interface on how to approach this.
• I've simplified the list of tanks to more general estimations, but you can add your own, should you feel the need. (Especially the list of US-sizes of tanks can be a bit off/weird, any ideas about that on the other side of the pond?)
• It's both in imperical and metric units, but the imperical units are a bit less tested.
• There's a default list of commonly used stuff, but you can add your own items pretty easily, either by volume and weight, or weight and buoyant weight.
• There's a balanced rig view, where you can easily compare the heaviest scenario and the lightest scenario, and play with the amount of weight you want to take.

Source code is available here: GitHub - arendvw/buoyancy-calculator: A scuba buoyancy calcualtor

Most relevant calculations and their source are contained in this file.

I'm curious what you think! Does it give useful enough results for you?