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

[Storker]

I have to confess that I haven't downloaded and played with your spreadsheet (mostly because I just discovered this thread, and that I suspect that you don't have euro standard tanks to choose from), but just a comment re. drysuits and weighting since you apparently have included drysuits in your suit list.

IME if you have a shell type suit, whether it's trilam, crushed neoprene or the good old Viking, the undergarments are a lot more important for your buoyancy than the type of suit. Also, with the same compressed neoprene suit, switching - or adding - undergarments will affect your buoyancy. Back when I had a compressed neoprene suit, I used more lead during winter simply because I wore more under the suit. My current undersuit is really voluminous and in my current configuration I need a lot of weight to be properly weighted. If i were to switch to a lighter undersuit, I'd probably have to take several kg off my belt, but I kind of like being comfy warm while I'm diving.

Tl;dr: have you considered that the choice of undergarments will have at least as much effect on the diver's buoyancy as the choice of drysuit?

 

[rsingler]

Happy to incorporate euro standard tanks if you'll send me specs and buoyancy data. We already have over EDIT: 150 tanks to choose from.

And yes, the liner is the key to drysuit buoyancy, as you pointed out.

 

[DavidFL]

@Storker, the spreadsheet has an entry for the thickness of the undergarments in mm; as far as I can tell, it uses some fairly complicated formula based on diver height and weight, and undergarment thickness, to calculate a 'body surface area' and then a 'body in suit surface area' that is further used in the drysuit buoyancy calculation. So the user of the spreadsheet definitely can make sure the spreadsheet is taking into account at least a gross approximation of the differences in buoyancy related to undergarments.

 

[Storker]

Happy to incorporate euro standard tanks if you'll send me specs and buoyancy data. We already have over 100 tanks to choose from.

As you probably know, euro standard tanks are characterised by their water volume and their service presssure. Water volume plus tank wall volume (which is the tank's mass divided by the density of steel) is the outer volume. When you have the mass and the outer volume, you have the tank's buoyancy (excluding the negative buoyancy of the valve, of course).

So, for any euro standard steel tank you only have to enter the tank's water volume and the mass, feed it into the appropriate formula, et voila! Empty tank buoyancy. Add the mass of the gas (given by #surface liters and the gas density) when full, and you have the full tank buoyancy.

 

[stepfen]

Any chance to get this in metric units too??? I understand it is pretty difficult to implement but I am sure it would be greatly appreciated by all of us living in the metric world.
I could help implementing this. For example I could take the latest version and convert it cell by cell to metric units but I don't think this is the smart way to do it, as the conversion will have to be done again and again for any newer versions.
There could be a cell to choose between metric/imperial to begin with and proceed accordingly but that would create a mess with all the formulas, units mentioned in cells etc.
Any neater way?
Thanks

 

[rsingler]

Yeah, that could be a bit of a challenge, but let me put some thought into the most efficient way to implement that. It's not overwhelming - just do all the calcs in one system or the other and convert the inputs and answers.

 

[rsingler]

So, for any euro standard steel tank you only have to enter the tank's water volume and the mass, feed it into the appropriate formula, et voila!

I suspect mass will vary by manufacturer, as will valve weight. Is there the same variability that we see with US tanks? E.g., an AL80 really only being 77.4CF? Is a 12l tank exactly 12l?
As I said, if you can get me the data, I'd be happy to put those tanks into the list.

 

[stepfen]

I
As I said, if you can get me the data, I'd be happy to put those tanks into the list.

Does that help??
https://www.subaqua.co.uk/cylinder-buoyancy.php

 

[rsingler]

Does that help??
https://www.subaqua.co.uk/cylinder-buoyancy.php

Yeah! If the volume is accurate, then I'll fudge the valve weight, do the calcs and add their buoyancies to the tank list. Thanks!

 

[Storker]

if you can get me the data, I'd be happy to put those tanks into the list.

The two biggest brands in my part of Europe are Faber and Eurocylinder.

Faber specs, company site: Faber Cylinders for Scuba Diving Catalogue
Eurocylinder haven't put up their spec sheet on their website, but you can find specs for singles here and for twinsets here.

For twinsets, you'll have to fudge in the mass of the manifold as well as the valves. Note that the small rec twinsets may be assembled either with an isolation manifold, or with just a simple manifold without an isolation valve. I really don't know how much that affects the weight, though.