Helium drysuit bouyancy

[broncobowsher]

I should point out that my Drysuit helium usage that was fine was ~30%. So a fairly light mix.
And there can be issues of counter diffusion. A good trimix class will cover that. Under normal usage, and even most non-normal usage, a non-issue.

But what hasn't been mentioned yet, flow rates through the valves. Helium (and helium mixes) flows better than air. And Argon flows really slow. How much gas you add to your suit per unit of time changes.

 

[Badger7]

Since we've moved into tangents... One thing not yet mentioned is the increased likelihood of DCS (primarily in the form of skin bends), since helium is small enough to diffuse through the skin.

Oh now that's an interesting nuance that I have not heard anyone express. You're saying that helium is more prone than nitrogen to absorb directly into the skin, dissolve into skin tissues, and then form bubbles on ascent?

I was willing to discount the thermal value issues (if it makes that much of a difference you're probably diving with heated undergarments anyway), but also adopt the financial argument (I'd rather stuff 6 cubic feet of air into my drysuit than 6 cubic feet of expensive trimix). I really hadn't considered any other aspects such as DCS, thanks for sharing that!

Reminds me of a funny little story from my childhood. My dad picked up dry ice from his office to fill up the bottom half of a big cooler for a camping trip out west. Worked great, everything stayed dry and cold, windows cracked for safety. What he didn't calculate was the C02 absorption through the skin of the fruit. After sitting in the cooler for a few days, we had slightly fizzy carbonated oranges.

 

[AJ]

An ali80 has circa 2100 litres of gas under great pressure (210 Bar); your drysuit contains a couple or three litres at ambient pressure.

Hence a few grams difference.

Although, if using helium, you’d need much thicker underclothes to cope with cold from the greater heat conduction

Yep, realized it now. Should be reading SB while working

 

[Pavao]

This one is a bit of a hypothetical, I’m not sure you want to use your helium trimix just to fill your drysuit
But if you were to fill with a helium mix instead of regular air would you experience more buoyancy due to helium being the lighter gas ?

Adding gas to suit and wing isn’t a dial with fixed increments, it is always an intuition about how much gas to add, specially the wing for buoyancy, and as you get closer to fine tuning your buoyancy, it becomes smaller injections.

If I didn’t make the point clear yet, here’s an alternative thought, do you experience more buoyancy when diving a wetsuit and filling your wing with trimix as opposed to air?

Answer should be no, you know the right amount of (any) gas to add when you FELT you’ve achieved neutral buoyancy.

 

[Searcaigh]

I've used a 18/40 mix on a few occasions with no difference in buoyancy although I did notice some difference in warmth. After that I used my EAN50 deco gas as I didn't have a separate drysuit bottle.

 

[nadwidny]

It is interesting to see that some say they have used a helium mixture in their drysuit. What temps are you doing this with? I'm guessing 70F-ish.

I dove with a guy who plugged into an 18/35 in a 40F lake and he got so cold that within 15 minutes he couldn't navigate his way around a site he had been in hundreds of times before.

 

[TrimixToo]

This one is a bit of a hypothetical, I’m not sure you want to use your helium trimix just to fill your drysuit
But if you were to fill with a helium mix instead of regular air would you experience more buoyancy due to helium being the lighter gas ?

No. But you *will* get colder. Much colder. He conducts heat far better than combination of N2 and O2.

 

[rduquesnoy]

It is interesting to see that some say they have used a helium mixture in their drysuit. What temps are you doing this with? I'm guessing 70F-ish.

I dove with a guy who plugged into an 18/35 in a 40F lake and he got so cold that within 15 minutes he couldn't navigate his way around a site he had been in hundreds of times before.

Water temp was about 60F and the dive itself was 45 minutes max. Don't think I would have taken the risk with 40F.

 

[nadwidny]

Water temp was about 60F and the dive itself was 45 minutes max. Don't think I would have taken the risk with 40F.

Yeah, 40f and a trimix suit gas isn't a good thing. My buddy he arrived at the site and we found out he forgot his suit gas cylinder. 80' max dive, 60' average. All he had was the trimix in his 104s. No deco needed and so no 50% was brought to use. So we thought "what the hell? How bad can it be plumbing into his trimix?"

It was bad.

 

[mr_v]

It is interesting to see that some say they have used a helium mixture in their drysuit. What temps are you doing this with? I'm guessing 70F-ish.

I dove with a guy who plugged into an 18/35 in a 40F lake and he got so cold that within 15 minutes he couldn't navigate his way around a site he had been in hundreds of times before.

Plugging a lean mix into the dry suit is not the first choice but the only one available in some cases.