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]

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%

What point are you trying to make with regard to the bouyancy spreadsheet?

 

[rsingler]

My fault. Faulty memory, that is.
It's 2.something% difference, as has been pointed out. The spreadsheet uses a mean value of around 1.025 for computing fresh versus salt water buoyancies, as I recall.
For people: four pounds, not four percent. In any case, insignificant for your rig.

 

[anchochile]

I'm trying to use this calculator to estimate how much lead & lift I would need with a single AL 80 and a 5mm wetsuit. I don't have access to a pool to measure my suits & rig buoyancy, so am using the following assumptions:

• Height 68 in, weight 147 lbs
• Max depth: 120 ft
• Personal buoyancy: -2lbs in Fresh Water/+1.2 Salt Water (I know I sink in fresh water at end exhalation, so this is a guess)
• Exposure: Suit Full 5mm (new/soft); Booties 8.5mm. Results in +18.2lbs buoyancy
• Rig -7.0lbs (5lb steel plate, 2x1lb steel-buckle tank straps, single-piece webbing harness, typical D-rings and bolt snaps)
• First stage weight: -1.5lbs (Sherwood Magnum SRB5300)
• Tanks: single AL80

It gives me a recommendation of 9 lbs lead and 17-22 lbs lift.

But then when I do a reality check & change it to 3mm suit, it tells me I need 5 lbs lead and 13-17lbs lift. I know that in reality, I don't need any lead with this rig when diving an AL 80 in 3mm suit.

Similarly, when I reality-check it for my cold-water setup (7mm suit + 5mm shorty, gloves, hood, single Steel 100 tank), it tells me I need 19lbs lead and 30-39 lbs lift. In that situation, I actually only use 10 lbs lead, and my 30-lb wing floats my rig easiliy and keeps my head far above the surface.

Given that it's 5 lbs off on the 3mm scenario, and 9 lbs off in the cold-water scenario, any suggestions on how to adjust my inputs above to get closer to reality and understand how much weight & what wing size would suffice a 5mm? Given the overestimate of lhe other scenarios, should I just assume I'll need somewhat less lead & lift than it suggests?

 

[Centrals]

Muscular person requires less weight while the opposite needs more!

Trial and error.

 

[inquis]

Got a neighbor with a hot tub? Or give your trash can a good cleaning and use that. The suit buoyancy is probably the biggest unknown in all this.

 

[happy-diver]

My buoyancy computer runs on water.
The more you go, the more you know!

 

[rsingler]

I'm trying to use this calculator to estimate how much lead & lift I would need with a single AL 80 and a 5mm wetsuit. I don't have access to a pool to measure my suits & rig buoyancy, so am using the following assumptions:

• Height 68 in, weight 147 lbs
• Max depth: 120 ft
• Personal buoyancy: -2lbs in Fresh Water/+1.2 Salt Water (I know I sink in fresh water at end exhalation, so this is a guess)
• Exposure: Suit Full 5mm (new/soft); Booties 8.5mm. Results in +18.2lbs buoyancy
• Rig -7.0lbs (5lb steel plate, 2x1lb steel-buckle tank straps, single-piece webbing harness, typical D-rings and bolt snaps)
• First stage weight: -1.5lbs (Sherwood Magnum SRB5300)
• Tanks: single AL80

It gives me a recommendation of 9 lbs lead and 17-22 lbs lift.

But then when I do a reality check & change it to 3mm suit, it tells me I need 5 lbs lead and 13-17lbs lift. I know that in reality, I don't need any lead with this rig when diving an AL 80 in 3mm suit.

Similarly, when I reality-check it for my cold-water setup (7mm suit + 5mm shorty, gloves, hood, single Steel 100 tank), it tells me I need 19lbs lead and 30-39 lbs lift. In that situation, I actually only use 10 lbs lead, and my 30-lb wing floats my rig easiliy and keeps my head far above the surface.

Given that it's 5 lbs off on the 3mm scenario, and 9 lbs off in the cold-water scenario, any suggestions on how to adjust my inputs above to get closer to reality and understand how much weight & what wing size would suffice a 5mm? Given the overestimate of lhe other scenarios, should I just assume I'll need somewhat less lead & lift than it suggests?

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.

 

[HKGuns]

Thanks for surfacing this thread, I decided to watch this thread as I can never find it thought the search menu and try to recommend it often as it has been so useful to me.

 

[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.

Thanks. I actually don't use a drysuit (for now), I'm diving wet in cold water with a 7mm IST semi-dry plus 5mm shorty oversuit. Sorry if that wasn't clear.

I'm going to measure the wetsuit thickness directly as you suggested. For smaller neoprene accessories (hood, boots, etc), I might try to measure their buoyancy directly in the bathtub in a mesh bag with lead weights. When transferring those numbers to the spreadsheet, is any fresh>salt adjustment needed since I'll be measuring in fresh water?

Thanks again for this awesome tool!

 

[inquis]

any fresh>salt adjustment needed since I'll be measuring in fresh water?

It's a 2.4% increase, which I would ignore for wetsuit buoyancies.