Question about learning deco procedures

[scubadada]

The problem is that nobody knows how Scubapro incorporates heart rate, breathing rate, or skin temperature into their algorithm calculations. One can safely assume that these variables would only make the base algorithm more conservative. Buhlmann ZH-L8 or 16 ADT MB are already quite conservative.

 

[KenGordon]

The manual for the G2 says you can turn off the heart rate and breathing stuff.

If underneath it is using the same compartments (as implied by the name) then you have a hope of matching. The computer has a built in planner so some simple experiments comparing plans in the depths of interest would be worth a go.

Of course he could also just plan the dive with the computer and put that on his slate.

Using NDL times to compare how conservative two computers will be on a deco dive is not a great idea. The NDL times will be based on the faster compartments which will have become well over saturated on a deco dive, since they are fast they will be first to desaturated leaving the middle compartments as the limiting ones for getting out at the end of deco.

Now mostly the compartments are similar, but the differences are amplified by the NDL calculation, especially the way presented by the SB’ers favourite computer review.

That computer looks perfectly fine. I’d be prepared to do a 50m dive on one going by the manual. I don’t think I have seen one being used though.

Again here is a computer that tries to take account of a bunch of factors known to influence deco and that is treated as a bad thing by a group of people who collectively ignored computers for years and years.

 

[Dan_P]

I've searched for the answer to this but can't find it. Is there a rec diver course that teaches how to make deco dives? I have been taught to never violate NDL, but I know people do make deco dives. Is this something that is only taught in tech diving courses? I am specifically asking about deco dives that are within recreational depth limits.

I know that nitrox is an option to extend NDL. Honestly I'm still working on improving my trim/buoyancy/SAC that I don't get near NDL anyway.

The terms "technical" and "recreational" are meaningless.

That’s why the term min deco is used.

I think what's really at play here, is diving within one's limit in general.
I personally find that there's a nasty trend for diving beyond them, for a range of reasons, and in my opinion, going into deco with a "recreational" training background solely, fits the bill.
This quote sums it up well:

Anytime there is a physical barrier (Cave or Decompression ceiling) to the surface the scope of diving is changed. Need proper training and dive management for this kind of diving otherwise one can pay with their life. So its not something to take lightly.

I subscribe to expanding my comfort zone during training, and diving within it outside of training.

Another reason in leading to the tech classes was the what if situation of accidentally entering deco and not really understanding what the obligation may be - you can't plan an accident but at least you can train for one.

I understand this argument, and have heard it before.
However, from a managerial position, the risk of divers (ab)using minimal knowledge obtained on how to plan decompression beyond their scope of training, far outweighs the relatiely minimal difference between crossing NDL and needing some deco, and drowning because that same diver will run out of gas at some point anyway if they stay at depth for too long;
Put differently, it's limited how much deco one can rack up, complete and make it to the surface, on a single tank.
And a bit of overshot NDL can be handled with O2 and a chamber ride instead of training for decompression planning per se.

That's my take on it, anyway.

As for doing it in a single tank, it is possible to do so if you use a single tank with a dual valve. You have to have two regulators on your primary gas supply so that if one fails, you can shut it down and go to the other. That is pretty rare, though.

I appreciate that it's rare in many places, and to be fair, the quote above refers to a specific course, not any general trend of using single-tank with a "pony" (to use more widely accepted terms, either "deco" or "stage") bottle.

With the growing trend to using using pony bottles on routine recreational dives, I would think the idea of getting more bottom time through a program like this would be popular. With a pony bottle, you are supposed to finish the planned dive on your primary gas with the pony in reserve. That would satisfy the requirement for the Tec 40 course as well. For your post course diving, you don't have to have a separate deco gas on your dive if you don't want to. The only difference between a basic recreational dive with a pony and a Tec 40 dive with a pony could be the fact that with the latter you can violate NDLs and do up to 10 minutes of deco.

Most of the divers I've seen opt for a stage bottle on a standard OW dive, did so because they wanted to do two dives but bring only a single rig, not because they couldn't find a tank that holds enough gas to do a single rec dive.
For that eventuality, it makes most sense to use the offboard (stage) first.
If one wants to do decompression dives, bringing a deco tank is a better option, as it'll hold a richer gas that allows faster decompression.
For that eventuality, it makes most sense to use the offboard (deco) first.

In the event of an OOG-scenario, I'd by far prefer to donate the stage from my mouth, rather than have to donate an offboard or do two OOG-rotations because my backgas is nearly empty.
In that eventuality, it makes most sense to use the offboard (stage) first.

Why does it make sense to start on the backgas?