Bent... advice sought on continuing to tech dive

[Tortuga68]

Thanks but the tissue loading graph is just a representation of hypothetical model - it's not showing what's actually happening in my body. It only shows the theoretical loading based on the algorithm/GF I have chosen to follow, which you already think are conservative.

What I mean is, if I change the data in my computer, the tissue loading graph will also change - but the actual gas loading in my body won't change for any given dive

 

[kensuf]

I'm going to be blunt here. If you're getting bent on a 30/70 GF (i.e. niggles, etc), you may have something wrong with you. Do yourself a favor and get tested for a PFO.

If you have a PFO, you have two choices -- quit tech diving (or diving altogether), or get it fixed.

Having had one closed a few years ago myself, I can say that it's life changing.

 

[rongoodman]

Thanks but the tissue loading graph is just a model, it's not representing what's actually happening in my body. It represents the loading based on the algorithm/GF, which you think are conservative

True, but it might illustrate how closely you're actually following the model that you've chosen to use.

 

[Tortuga68]

I'm going to be blunt here. If you're getting bent on a 30/70 GF (i.e. niggles, etc), you may have something wrong with you. Do yourself a favor and get tested for a PFO

I appreciate both the bluntness and the feedback, but I don't have a PFO

 

[Tortuga68]

True, but it might illustrate how closely you're actually following the model that you've chosen to use.

There's a better way to do that

 

[KenGordon]

my idea would be rather to extended the initial stop times when the oxygen-window is first opened at high PP

My naive view is that you are diving in a style which tries to protect fast compartments, but getting hits in tissues modelled by the slower compartments.

Well... isn't that the job of the decompression algorithm? Are you saying I should use a different GF?

I am saying that extending the first stop and using a low GF low (like 20 or 30) are going to tend to protect the faster compartments at the expense of the slower compartments. To protect the slower compartments you want a longer shallow stop. Your shoulder issue sounds to me (and I am absolutely not an expert) to be a slower compartment problem.

The decompression algorithm has knobs on. You have them turned one particular way. You could mess with the knobs to try to adapt it or you could explicitly add extra at then end. The trouble with turning the knobs is they feed back to the rest of the ascent.

Also, that algorithm doesn’t explicitly track repetitive diving or multiday diving. It is all about the disolved gas. Deco is probably more complicated than that, hence advice about taking days off etc.

See and
The second one about 35 in minutes is relevant to my point about fast vs slow.

 

[KenGordon]

Another thing about these compartments, GF, m values etc.

People often think that the surfacing GF will make up for a slow ascent, deep stops or whatever by limiting the the surfacing over saturation. However it only limits the leading compartment. So, for example, compare plan A with compartment 1 at 10%, 2 at 40, 3 at 100, 4 at 40, 5 at 30 6 at 20 and the rest at 10 and plan B with 5%, 30, 90, 95, 85, 80, 75 etc then plan B will be allowed to surface but all the extra saturation in the non leading compartment is ignored.

 

[kensuf]

I appreciate both the bluntness and the feedback, but I don't have a PFO

If you've been tested by TEE, and tested negative, that doesn't necessarily mean you are in the clear. I know several people that had false negatives on the TEE but tested positive (and had PFO's closed with success) via other methods.

 

[rjack321]

Getting bent twice in 1500 dives is just how the dice roll. I'm going to disagree with @kensuf here, its totally possible to get bent on 30/70. Recreational divers think of that as "super conservative" but its not in the grand scheme of things. Compare with the commercial deco profiles published this month in DAN. They do WAY more deco than us fun divers do. Alert Diver | Anatomy of a Commercial Mixed-Gas Dive

Going forwards I would:
1) Add helium where you can, there is no "residual helium time" on repetitive dives. Even if there was, the maximal offgassing gradient at the surface is eliminating it super quick.
2) move up the GF 30low to 50ish, don't add any deep stops.
3) extend your O2 time, especially on the second dive. E.g. Do all your o2 time at 6m. Once your shearwater is clear at 6m spend an additional 10mins at 3m. Don't extend 50% stops, move efficiently through the 50% stops and get to the O2, if this is a repetitive dives "problem" its the slow tissues that are your issue.
4) Limit yourself to one 50-60m dive a day, if you are going to do a repetitive dive make it shallow (<40m) and do extra deco. (not ideal but an idea)
5) Keep the 3+hr surface intervals
6) Work out and lose some weight
7) Get a thicker wetsuit or even a tropical drysuit, make sure you are downright toasty on deco
8) Guzzle water before and during dive days

(I can dig up citations evidence but in the interest of brevity left those out)

 

[boulderjohn]

since my idea would be rather to extended the initial stop times when the oxygen-window is first opened at high PP.

That's what I'm talking about yes, aka the S-curve in Ratio Deco.

Yes, you did miss the memo. The idea of the S-curve was not well-founded in science to begin with, and never made sense to me when I was required to use it in my training. GUE has dropped it.

Well... isn't that the job of the decompression algorithm? Are you saying I should use a different GF?

I am saying that extending the first stop and using a low GF low (like 20 or 30) are going to tend to protect the faster compartments at the expense of the slower compartments. To protect the slower compartments you want a longer shallow stop.

I agree with Ken. I would raise the GF low a bit so your first stops are not so deep.