Buoyancy, Balanced Rigs, Failures and Ditching – a comprehensive tool

[rsingler]

In response to your input, attached please find the newest iteration of the Buoyancy Estimator.
Errors in the salt water formulae were corrected.
A minimalist ability to compute for fresh water was added.
European tanks were added to the list. I'm sorry, but at this point, having a separate Metric only version was more than I could tackle. The spreadsheet is still the odd mix of Imperial and metric data common in the US market (Cu Ft for tanks, Millimeters for wetsuit thickness, etc.).
The fourth order polynomial formula for wetsuit compression was changed based upon new data.
That's the good news.

The bad news is that as with any iterative big system, it's a little difficult to take in all at once.
So if you're new to this thread, please start at the beginning and read the various posts.
Once in the spreadsheet, start at sheet #1 and work your way through. There are LOTS of directions buried in the individual sheets.
Especially useful is the multi-window approach to experimenting with the toy, as described in post #2.

The new versions have been added both here, and in post #1.
As always, please comment in the thread with your suggestions or criticisms. We've come a long way.
And most important of all, I depend on your feedback for accuracy. If you find a mistake, as a few others already have with such a big file, just let me know and I'll fix it as soon as I can.

Just for grins, our starting data is with a medium sized guy with lots of neoprene and a large steel tank. A perfect way to reignite the argument about balanced rigs. Have fun looking to see how (with BOTH a BCD failure and a disappearing buddy) he's 15-18# heavy at 80 feet due to wetsuit compression. He maybe can't swim that up. But by jettisoning just a few pounds, he's able to get off the bottom (assuming he can swim up 12# for 20 feet or so), and becomes neutral at the usual safety stop depth. After offgassing for as long as his air allows, he can now slowly ascend with slight positive buoyancy to the surface, arriving with minimal chance of decompression stress, after an otherwise fatal scenario. Without re-igniting the redundant lift wars, let's just say that from a theoretical standpoint, it's nice to know that there's one more rescue option you can put in your bag of tricks. And it's my personal belief that, employed properly, this partial weight jettison provides a safer return to surface than ascending on a lift bag and reel. But of course, your buddy didn't leave you, and even if he did, using a sausage to get you off the bottom, and then releasing it when wetsuit re-expansion sufficiently assists your negative buoyancy ascent remains a fine choice.

EDIT:
Fresh water corrections improved. V24 deleted. New V25 uploaded.
EDIT:
Error found in hood buoyancy calc cell.
New versions loaded below.

 

[rsingler]

Error discovered in Hood buoyancy calculation cell.
New spreadsheets loaded here and in Post #1 as Version 25b.
EDIT: this version superceded. See below.

Drysuit Reserve Buoyancy is underestimated for thin liners.
A revision has been posted below and the spreadsheets in this post have been removed.

 

[DavidFL]

Thanks for all your effort to continue the improvements and refinements. I'm particularly interested in the drysuit buoyance calculations, since I have been using my drysuit over the winter here in FL with the thinnest of undergarments; and finally used it in relatively cold water in the Pacific Northwest last November. And the freshwater work is very welcome; I did a Fundamentals Part 1 class in Florida freshwater a few weeks ago. I have a weeklong trip to God's Pocket in BC in the calendar in September. This spreadsheet continues to give me guidance with every gear and configuration change!

 

[rsingler]

A second major revision is slowly taking shape. It will finally make the complete Imperial to Metric conversion, incorporate some formula improvements regarding wetsuit compression, and improve the layout.
Layout changes remain a major focus. This thing is so large that we need every bit of help we can get to stay oriented.
@DavidFL , let's just say that for warm water single tank drysuit diving, there are few configurations where true reserve drysuit buoyancy is not enough to make up for wing failure. But I'll have that quantified in an intermediate release soon.

 

[Pavao]

I’m on my phone and can’t quite play with it, how much data is needed to be input, in other words, can someone do it for me?

I confess I just skimmed through the thread, but do I understand this tool is to help figure out weighting needed? And yes, I understand use my training, I’m just curious what kind of numbers it would spit out for me

 

[rsingler]

Due to the interest expressed above, I've gone ahead and finished the corrected Reserve Drysuit Buoyancy calculations and have reloaded revised spreadsheets in this post and in #1 above.
The rationale behind the change is as follows:
The spreadsheet initially calculated reserve drysuit lift as a flat 15% of drysuit buoyancy, to be conservative.
For warm water drysuit users, it is clear that there's LOTS of room left in a drysuit before a seal leak, when using a thin liner. Conversely, for really cold water drysuit divers, the reserve lift of the suit may be limited by the fact that the liner is already puffing the suit out near its max capacity.

The new formula adds the lift of an additional 5mm of liner height in calculating reserve lift. The amount added decreases above 7mm liner thicknesses however, and is limited to a flat 10% additional buoyancy above 13mm liner thickness. Again, these calculations should be conservative.

As always, these formulae are only approximations of what we think is happening. The data should not be relied upon as a primary determinant of weight requirements, and a pre-dive buoyancy check should always be performed with a new configuration.

New revisions (including the repeatedly requested Metric conversion) are still in the works as noted above, so stay tuned.

Dive Safe!

EDIT: Formula error corrected. V25d loaded
EDIT: Spreadsheets deleted in favor of new version. See Optimal Buoyancy Computer sticky thread in Advanced Forum.

 

[rsingler]

Does the dry suit buoyancy data and assumptions pertain to all types of dry suits? Is the trilaminate the same as the crushed neoprene in the assumptions for example? Also undergarments, I know I use less with my neoprene suit than other divers use that dive trilaminate suits.

My early reply to you was incomplete. A new version of the spreadsheet is in the works to account for differing drysuit shells.
The theory we are implementing (after some experimentation), is as follows:
As noted before, a trilam suit shell is assumed to be neutrally buoyant, and lift is provided only by the air trapped in the loft of the liner, or in folds of the suit.
A Crushed Neoprene suit is slightly negatively buoyant. Due to its thicker/stiffer texture, the shell is assumed to trap slightly more air in the folds with thin liners, as well as be slightly negatively buoyant in itself.
A Neoprene drysuit essentially has a thin wetsuit surrounding the liner. Therefore, due to the extra insulation of the neoprene, a thinner liner can be used for much diving. But the neoprene is compressible with depth and loses some buoyancy and insulation on descent. The shell itself is therefore positively buoyant in addition to the air in the liner loft.
A Compressed Neoprene Suit essentially has the equivalent of a much thinner wetsuit surrounding the liner. While its buoyancy is less, it is still positively buoyant. It is assumed to have slightly less susceptibility to buoyancy loss with depth.

The factors we plan to implement into the buoyancy formulas for drysuit diving are tentatively as follows. We recognize that we can't account for all of the variations, but wanted to get closer to the changes that occur at depth than with our previous formula.

1) Trilam buoyancy is unchanged at depth due to added air to keep liner thickness constant (unlike a wetsuit). This formula is unchanged.
2) Choosing "Neoprene Drysuit" will be assumed to be equivalent to wearing a 3mm wetsuit shell around the liner. It is assumed that a thinner liner will be used as a result.
The formula will leave the liner buoyancy unchanged with depth, as air is added to the drysuit. The formula will assume compression of the shell like a "New Standard" wetsuit. Thus, the total buoyancy of a Neoprene drysuit will decrease slightly with depth. Additional air added to the suit will compensate, so actual buoyancy will remain unchanged. However, the spreadsheet will assume a decrease in buoyancy, as air added will eat into the reserve buoyancy the suit has before a seal begins to leak, for wing failure computations.
3) Choosing a "Compressed Neoprene Drysuit" will be treated the same as a neoprene suit, except that the inherent buoyancy of the shell is assumed to be only equivalent to a 1mm wetsuit. Buoyancy loss is therefore much less, and liner thickness will still be the primary determinant of total drysuit buoyancy.
4) Choosing a "Crushed Neoprene Drysuit" will be treated like a Trilam with respect to buoyancy loss at depth (i.e., none), as air is added to the suit to keep liner loft constant. However, when a thin or no liner is worn beneath the suit, the formula assumes that some air is nonetheless retained in the thicker folds of the suit, resulting in slight positive buoyancy until liner thickness reaches 3mm. The inherent negative buoyancy of the crushed neoprene fabric is assumed to be a flat additional 2lb/1kg and is not further corrected for body size as the variability is less than 1lb/0.5kg.

I dive a Trilam suit, so I'm working with data from my examination of other suits and comments from my brethren, rather than personal experience.
Before this new version is posted, I'd welcome any input from drysuit divers who use shells other than Trilam, to help me fine-tune the formula before release.

BTW, this new version will also fully implement Metric units, for those who have been waiting.

 

[rsingler]

Within the next week, we will be releasing a completely new spreadsheet. While some elements from previous versions will be retained, we have had extensive input and helpful criticism that has improved data entry, formulas and output. The new features about to be released will include:
1) Salt or Fresh water results
2) Metric or Imperial units
3) U.S. and European tanks
4) A completely new drysuit arrangement, with separate computations for trilam, neoprene, compressed neoprene and crushed neoprene shells
5) A comprehensive User's Manual to help with wading through this large tool.

Perhaps most important, the first tab after data entry will be a SIMPLE output of weight and lift required, to satisfy the many who have no interest in all this numbers stuff, but just want to get prepared for that vacation dive in a completely new and different environmental suit.

Thank you to @kmarks , @-JD- , @johndiver999 , @PfcAJ , @boulderjohn , @Dan_P , @DavidFL and others, who wittingly or unwittingly provided critical advice or information that made this tool possible.
Special thanks to @stepfen for his exhaustive feedback and suggestions, and to my recently-certified son Douglas, whose millenial approach to a complex tool prompted improvements in layout.

When the new spreadsheet and manual is released, a link will be provided to a new thread, and this thread will be closed.

 

[stepfen]

Thanks and congratulations for all the hard work should go to you @rsingler
We all owe you at least a beer for this! If you drink, lucky you. If you don't, well, bad luck

 

[rsingler]

You underestimate your contribution. Couldn't have done it without you.