Maximizing bottom time safely

[rjack321]

Option two is to set conservatism to max (35/75 I think), ensure that my surface gf doesn’t go above 95 and that my tts is within my available gas. This is technically a deco dive, but only because of conservatism settings.

This is a really bad idea - and there is nothing "safe" about it. Just playing with your GFs doesnt mean you know how to deco dive, plan adequate reserves, or solve problems. And there was zero mention of a buddy. Self training on deco diving while alone is just not good.
Can you even hold a midwater stop adequately (odds are you can't)
What happens when you discover your SPG was stuck and you're OOA?
What happens if the peregrine dies?
Regulator goes tits up?
Shoot a bag and do these deco stops?
End up staying 5mins longer and 3m(10ft) deeper than your plan?
So many ways to have a really bad day, got good medical and life insurance?

 

[L13]

OTOH, if I understand it correctly your Option 2 is not a good idea. Let's say you leave the bottom with your SurfGF reading of 95. What do you think is going to happen to it while you are waiting out the deep deco stops that a GF Lo of 35 is likely going to require?

The answer is that it's going to keep climbing. Likely to the point where you have turned your pretend deco dive into an actual deco dive. A deco dive that you are not trained for and probably without the gas reserves you would have on a planned deco dive.

This is wrong.

His SurfGF will start dropping by the time he reaches his first "deco" stop, and continue to drop on the stop.

Using his option 2 in SubSurface:

For a 60' dive​

55min to SurfGF=95. Arrive at first stop SurfGF=93 GF99= 57, drops during stop to SurfGF = 75, peak GF99=58. First stop is driven by 19min tissue (long dive). He will need to stay at 10' for 11min to get SurfGF down to 75.​

For a 120' dive​

10 min to SurfGF=95. Arrive at first stop SurfGF=92 GF99=32, drops duing first stop to SurfGF=90, peak GF99=56. First stop is driven by 5min tissue (short dive). He will spend 4 min between 30' and surfacing.​

​

His plan will work as expected.

Edit:
While the plan will work as expected for GFs, it is probably still a bad idea for many of the other reasons mentioned.

 

[Bazzathemammoth]

Why do you care a
Your options are completely different things.

Option 1 is acceptable given your current training level. Set the gradient factors to whatever you think is your appropriate risk level (or just accept the least conservative of the rec options), ride that NDL right to 1, ascend and extend your time shallow until you are happy with the SurfGF number and then very slowly surface. You obviously need to keep an eye on your remaining gas while all this is going on

OTOH, if I understand it correctly your Option 2 is not a good idea. Let's say you leave the bottom with your SurfGF reading of 95. What do you think is going to happen to it while you are waiting out the deep deco stops that a GF Lo of 35 is likely going to require?

The answer is that it's going to keep climbing. Likely to the point where you have turned your pretend deco dive into an actual deco dive. A deco dive that you are not trained for and probably without the gas reserves you would have on a planned deco dive.

Thank you for that, I hadn't considered that the deep stops might push me into actual deco territory. Option 1 it is. EDIT: or not?

 

[rjack321]

This is wrong.

His SurfGF will start dropping by the time he reaches his first "deco" stop, and continue to drop on the stop.

Using his option 2 in SubSurface:

For a 60' dive​

55min to SurfGF=95. Arrive at first stop SurfGF=93 GF99= 57, drops during stop to SurfGF = 75, peak GF99=58. First stop is driven by 19min tissue (long dive)​

For a 120' dive​

10 min to SurfGF=95. Arrive at first stop SurfGF=92 GF99=32, drops duing first stop to SurfGF=90, peak GF99=56. First stop is driven by 5min tissue (short dive).​

​

His plan will work as expected.

Every beginning tech/deco diver ever, when faced with a problem on the bottom either 1) ends up shooting to the surface (very rare) or 2) stays wayyyyy too long on the bottom dinking around burning gas and accumulating far more deco than the original plan. And those are the trained ones. The untrained make even more mistakes compounding the original problem.

It's not a good plan to try and thread this needle between GF95 representing deco and GF75 representing not really deco yet. This plan #2 will work on paper, right up until the OP gets wet.

 

[Bazzathemammoth]

This is a really bad idea - and there is nothing "safe" about it. Just playing with your GFs doesnt mean you know how to trdeco dive, plan adequate reserves, or solve problems. And there was zero mention of a buddy. Self training on deco diving while alone is just not good.
Can you even hold a midwater stop adequately (odds are you can't) - Yes, thanks for the pre-judgement.
What happens when you discover your SPG was stuck and you're OOA? - I'd notice before going ooa
What happens if the peregrine dies? Backup computer.
Regulator goes tits up? Backup regulator (twins are great aye)
Shoot a bag and do these deco stops? I don't know what you mean, I use my DSMB all the time.
End up staying 5mins longer and 3m(10ft) deeper than your plan? Then I'm an idiot. I've never accidentally gone past NDL, so im not sure how this is an issue.
So many ways to have a really bad day, got good medical and life insurance? Dont need it in NZ thankfully

I was waiting for this response. See my answers in your quoted text.

Every beginning tech/deco diver ever, when faced with a problem on the bottom either 1) ends up shooting to the surface (very rare) or 2) stays wayyyyy too long on the bottom dinking around burning gas and accumulating far more deco than the original plan. And those are the trained ones. The untrained make even more mistakes compounding the original problem.

It's not a good plan to try and thread this needle between GF95 representing deco and GF75 representing not really deco yet. This plan #2 will work on paper, right up until the OP gets wet.

Can you give me some examples? I can see how it would be easy to stay on the bottom too long while trying to fix something. That's a good thing to remember.

 

[L13]

Thank you for that, I hadn't considered that the deep stops might push me into actual deco territory. Option 1 it is. EDIT: or not?

If you leave the bottom at SurfGF < 95% you will not have a deep stops issue. But if you do it on a long shallow dive you will have a very long safety stop. for a 40' dive it would take 165min to get to SurfGF=95, and an 19min stop at 10' to get it back down to 75.

Still, for the other reasons mentioned by others, it probably isn't the best idea.

 

[L13]

Can you give me some examples? I can see how it would be easy to stay on the bottom too long while trying to fix something. That's a good thing to remember.

You weren't asking me. But for my example above of a 10min dive to 120', if you stayed 1 extra min your SurfGF=102 (Always a REAL deco dive), and takes 2 min to get below 95. Don't do it.

 

[Bazzathemammoth]

Thanks. I think option 1 is the go. I don't think that ill be doing any 165min dives any time soon, but it's good to be aware of the influence of long and shallow diving on deco times.

You weren't asking me. But for my example above of a 10min dive to 120', if you stayed 1 extra min your SurfGF=102 (Always a REAL deco dive), and takes 2 min to get below 95. Don't do it.

I was thinking more of examples of people he's seen do this. I understand the theory.

 

[admikar]

Can you tell me what I’m missing, or point me to some reading that could explain it?

You can thank me later.

 

[Brett Hatch]

Agree with other posters above that option 2 is a terrible idea. Option 1 is pretty reasonable, and as you learn more about these things, you'll be in a better position to reason about them.

Have you read Mark Powell's Deco for Divers book? If not, I think that is a great place to start to understand this kind of thing. The 2nd edition is available on Amazon for +/- $60 NZD. I learned a bit here and there on places like ScubaBoard and YouTube, which was great, but I never felt like I really understood the whole picture. But that book helped immensely, and after having read it once all the way through, I often use it as a reference again and again. The target audience for that book is not tech divers, or math geeks. It's any diver who wants to understand this stuff, no tech diving or fancy math background required.

edit: @admikar beat me to it! anyway, great book