Question When do we speak of technical diving ?

[steinbil]

It’s funny on a no deco dive to 130 feet I use less air than a shallower dive. It’s a common misconception about all the air you need since the time becomes the constraint.

While you are right that the actual gas usage on the shorter/deeper dive might be lower, the gas requirements for the dive is much greater if you do any sort of reasonable gas planning, which to be fair you do mention in the next post:

It can also depend upon what assumptions you make for emergency reserves and your buddy’s air consumption rate , but do a calculation and show us your results. Say for a dive to 60 versus 130 or 40 versus 80 feet.

This is a big caveat! With an estimated SCR of 15L/min (and 30L/min for a diver in panic), GUE mingas for bringing 2 divers to the surface with a single AL80 cylinder would look like this:

60ft/20m: 920L = 90bar / 1200psi in AL80
130ft/40m: 2580L = 240bar / 3400psi in AL80

This is why some divers talk about gas requirements for a 130ft dive, and why a single AL80 is an interesting choice...

 

[Degenerate]

I'm going to stick with my deco diving not being technical diving but sports diving. Says so right in my BSAC training manuals lol.

Does the modern BSAC training manuals say the same thing?

 

[johndiver999]

LOL, I'm not talking about GUE stuff. I am surprised people are surprised by my comments, but the conclusion would be obvious if people actually did a good bit of nodeco dives at varying depths.

Not that I am recommending it, but it is possible to do a solo drop to well past recreational depths for a quick bounce on an 80 cuft tank and leave the bottom with a lot of gas and no deco ceiling.

This is a very basic concept and also exemplifies how people can get in trouble on a deeper dive if they are used to only diving shallower. These "Shallow" divers may have become accustomed to just looking at their remaining air (or more likely nitrox) supply (gas pressure) and fail to pay a whole lot of attention to the remaining no-deco time. In other words, dive after dive, over and over, they get low on gas and have to come up - without paying much attention to nitrogen loading.

Now they drop down 130 or more and play the same game (watching air supply, and ignoring nitrogen absorption) and all of a sudden they have gone well into deco without realizing it and in a pretty short period of time and with relatively little gas consumed. This is counter intuitive to some people.

Now they got a real problem; they have significant deco and are deep and might not have the gas required for the safe ascent and the hang time - not withstanding the potential for needing to help out a buddy.

You can make it up from a deep dive pretty quickly and without using too much gas, just as long as you have no deco.

 

[Blackcrusader]

Does the modern BSAC training manuals say the same thing?

No idea I haven't seen a recent one lol. I do know when I do deep dives and stay within NDL I tend to not be an air hog.
I sucked 20 bar taking six minutes do get down to 45m to retrieve a camera another diver had lost.

Good thing I never exceeded NLD and had to do a deco stop

 

[Degenerate]

No idea I haven't seen a recent one lol. I do know when I do deep dives and stay within NDL I tend to not be an air hog.
I sucked 20 bar taking six minutes do get down to 45m to retrieve a camera another diver had lost.

Good thing I never exceeded NLD and had to do a deco stop

Maybe you should take a look at one then, maybe you wouldn't be telling people that decompression diving is recreational diving because it really isn't when you look at the added risks that come with it.

And also, nice humble brag I guess?
Not sure what anything after your first sentence had to do with this topic at all.

 

[steinbil]

LOL, I'm not talking about GUE stuff. I am surprised people are surprised by my comments, but the conclusion would be obvious if people actually did a good bit of nodeco dives at varying depths.

Not that I am recommending it, but it is possible to do a solo drop to well past recreational depths for a quick bounce on an 80 cuft tank and leave the bottom with a lot of gas and no deco ceiling.

This is a very basic concept and also exemplifies how people can get in trouble on a deeper dive if they are used to only diving shallower. These "Shallow" divers may have become accustomed to just looking at their remaining air (or more likely nitrox) supply (gas pressure) and fail to pay a whole lot of attention to the remaining no-deco time. In other words, dive after dive, over and over, they get low on gas and have to come up - without paying much attention to nitrogen loading.

Now they drop down 130 or more and play the same game (watching air supply, and ignoring nitrogen absorption) and all of a sudden they have gone well into deco without realizing it and in a pretty short period of time and with relatively little gas consumed. This is counter intuitive to some people.

Now they got a real problem; they have significant deco and are deep and might not have the gas required for the safe ascent and the hang time - not withstanding the potential for needing to help out a buddy.

You can make it up from a deep dive pretty quickly and without using too much gas, just as long as you have no deco.

The point you made about not just following your gas usage but paying attention to the NDL on a deeper dive is absolutely valid (although it should be a given that a properly trained certified diver would pay attention to both gas and NDL in planning and execution).

I was not at all surprised by your post, and don't conflate me with those who said you were wrong. It was just that you responded to those who mentioned that gas requirements for deeper dives were a factor, so I wanted to point out that with proper gas planning, 30-40m is a practical cutoff for recreational diving because of the gas volumes required.

PS.
I see now that you responded to Wibble who said "gas consumption", so in that context your comment makes even more sense. But still, gas requirements still kick in.

 

[scubadada]

The point you made about not just following your gas usage but paying attention to the NDL on a deeper dive is absolutely valid (although it should be a given that a properly trained certified diver would pay attention to both gas and NDL in planning and execution)...

A few years ago, I made some calculations for no stop dives at various recreational depths using air, 32% and 36% (common for shallower dives in FL) I mainly wanted to see if I was limited by gas or NDL. I used my avg RMV and an AL80 (my most common rental cylinder) for the calculations. I found the results interesting, easy to replicate this. I used MultiDeco to calculate the gas use.

 

[rx7diver]

Let us say a divers SAC rate has been previously calculated at .75 FT3/min.

That Diver goes to 66 feet(3 ata), dives a square profile stays 30 mins
That diver uses (.75 X 30 X 3) = 67.5 cubic feet used.

Same diver, same time same square type profile at 99 feet(4 ata) (.75 X 30 X 4) = 90 cubic feet used.

Careful: Navy tables give the NDL of a 100 fsw dive is 25 min (rather than 30 min), followed by a direct ascent to the surface using a 60 fpm ascent rate. And the NDL of a 70 fsw dive is 50 min.

Okay. These are the two dives you might compare with respect to expected air consumption.

ETA: I just read the posts that follow @Capt Jim Wyatt's. So, suppose, instead, the dives to 100 fsw and 70 fsw will be done using EAN32 (rather than air). It's straightforward to compute the two END's here, and then compute and compare the associated expected air consumptions of the two NDL EAN32 dives.

rx7diver

 

[Capt Jim Wyatt]

I never considered the aspect that you guys were staying within the NDLs.

I don't think I have done a dive in several years that did not require some staged decompression. Just this week alone I have made three dives to around 100 feet for 55-60 minutes.

 

[L13]

I never considered the aspect that you guys were staying within the NDLs.

But you snipped his post to start with exactly that statement(that wasn't even the start of the sentence):

on a no deco dive to 130 feet I use less air than a shallower dive.

Please explain how this is possible?

I don't think I have done a dive in several years that did not require some staged decompression. Just this week alone I have made three dives to around 100 feet for 55-60 minutes.

And? Relevant how?