What makes us think we can trust any of them

[DivesWithTurtles]

Ya know, maybe I'm agreeing with those folks saying that the "shape" of the ascent is what it's all about, but disagreeing on what that shape should be. Based on on Marroni's work, the shape should have steeper inclines to the steps and longer flat parts. Less smooth curve and longer landings on the stairs.

 

[Snowbear]

If you draw out deep stops or your deeper ascent is too slow, yes, you will continue to ongas. That ongassing still needs to be taken care of during the shallow stops. But this is starting to get more into the technical diving realm rather than non-tech recreational so-called "NDL" diving, where simply offsetting the ongassing that occurs below 3 atm with time spent wisely above 2 atm takes care of "cleaning up."

 

[Snowbear]

Based on on Marroni's work, the shape should have steeper inclines to the steps and longer flat parts. Less smooth curve and longer landings on the stairs.

This theory is disagreed with by some others that think the curve should be smooth, rather than the "bend and treat" profile of steps and stops....

 

[100days-a-year]

Hey,isn't that what Hill said.~A constant ascent rate VS. discrete stops.What exactly was the outcome of those experiments?

I personally chose to to take an active role in ensuring all the other criteria(hydration,fitness etc.) for safety are met so that I can fudge when it comes to decompression.I dive the most liberal computers possible sometimes 4-5 dives a day and up to 7 days straight several times a year and up to 35 days straight during the summer.Since perfusion isn't instant a discrete stop seems to allow the offgassing inert gas more "opportunity"at a higher avg depth than a slow ascent.My profiles when downloaded are usually as follows

Direct descent ,little yoyoing followed by a fast ascent rate to my 1st deepstop(1/2 max)A slower ascent to 30' or so and then a normal <30'FPM ascent to deco stops or the surface if NDL(rare)

Either I and most of the guys I spearfish with are anomolies...... or hydration,no nicotine/alcohol/little or no caffeine the day of and night before as well as cardio-vascular conditioning are a bigger issue than what method or source of info you rely on.

 

[DivesWithTurtles]

This theory is disagreed with by some others that think the curve should be smooth, rather than the "bend and treat" profile of steps and stops...

Marroni's work is not theorizing, it's testing and statistical analysis of Haldane's original work. And although "some others" may think the curve should be smooth (like Hill did), Marroni's analysis is rather compelling.

The idea of "bend and treat" (which is ascending directly to the shallow stops without deeper stops, then spending more time shallow), apparently can be attributed to the U.S. Navy, not Haldane. Haldane (like the more modern VPN and RGBM theories) suggested deeper stops. Don't confuse "bend and treat" with a Haldanian "profile of steps and stops".

Snowbear, did you read this (at least, if not this)? Did you see the statement by Bennett, "What is interesting, and not necessarily intuitive, is that an in-water stop with a relatively rapid ascent rate appears to be more effective at eliminating inert gas than a very slow ascent rate."?

Both you and I are advocating deep stops. The question is how to get to them and how to get from one to the next.

Hey,isn't that what Hill said.~A constant ascent rate VS. discrete stops.What exactly was the outcome of those experiments?

Yep. That's what Leonard Hill theroized. And Hill's theory has been discredited v. Haldane's stops.

I think the outcome of the experiments of both of them was "Mutton for dinner again!".

 

[Charlie99]

Hey,isn't that what Hill said.~A constant ascent rate VS. discrete stops.What exactly was the outcome of those experiments?.

Marroni's work is not theorizing, it's testing and statistical analysis of Haldane's original work. And although "some others" may think the curve should be smooth (like Hill did), Marroni's analysis is rather compelling.

IMO the key problem with Hill's ascents is NOT that they were smooth, but that they were linear. In other words, he was doing a constant speed of ascent rather than one that slowed as you get nearer to the surface.

The Marroni studies shows that a constant 3m/min (10 foot per minute) ascent had one of the highest amounts of doppler bubbles, even though it was one of the longer total time to ascend. A classic Hill ascent profile, with the same results as noted 100 years ago. What is amazing is that people are still recommending that style ascent --- the 30 second move + 30 second stop every 10' all the way to the surface that is being taught by some instructors has the same drawbacks as a smooth, continuous, linear/constant rate Hill-type ascent.

OTOH, the best profiles in the Marroni study had 5 minute stops at 15m/50' and 6m/20'. Whether the ascent rate elsewhere was 10m/min(33fpm) or 18m/min (60fpm) didn't have much effect. If you step back from the profile graph a bit; squint a bit; or were you to just mathematically smooth the profile to a series of 1 minute average depths, you can see that those two profiles are pretty close to each other.

Take any decompression program. Either crank in a very long time, or preferably, a dive to around or just slightly beyond commonly accepted NDLs but run with very high levels of conservatism / low values of gradient factors, etc. Look at the shape of the decompression curve. That's the curve you want to follow to get the best offgassing / best safety margin in a reasonable time.

Now play around with changing the distance between stops from 10' down to 5', down to 2' (you'll have to allow minimum stop times of less than 1 minute). The overall curve gets smoother and smoother, but there isn't really much difference in decompression time.

It's the overall SHAPE that counts. It doesn't matter if one gets that shape with a continous, BUT VARYING, ascent rate; or if one approximates that shape by a series of stops and ascents. On a practical basis, it's much easier to do a series of stops.

Hill, LINEAR, 1 minute per every 10' -- those are bad.

A smooth VARIABLE rate ascent or the approximation of that same VARIABLE rate ascent (becoming slower as one goes shallower) through a series of stops are pretty much equivalent.

 

[StSomewhere]

Withdrawn.

 

[Charlie99]

I have a Suunto Vytec, I think most would agree is the more conservative computers.

But there is nothing conservative or even sensible about ascending directly to 15' for 3 minutes and then pop to the surface after a dive with a max depth of 90' and average depth of 60'. Forget whether the rest of the algorithm makes sense, the ascent profile and safety stop is downright ridiculous.

Fortunately I can at least use it as a bottom timer and depth gauge that allows me to download dive profiles.

Please explain why you think the Suunto is commanding you to ascend directly to 15' for 3 minutes and then pop to the surface.

Does your Suunto object in any way when you execute the ascent and overall dive profile that you prefer?

 

[StSomewhere]

Please explain why you think the Suunto is commanding you to ascend directly to 15' for 3 minutes and then pop to the surface.

Commanding is probably a strong word, but that's all the Vytec/Vyper/Cobra etc. computers "credit" you for.

Does your Suunto object in any way when you execute the ascent and overall dive profile that you prefer?

My profile consists of 1 minute stops every 10 feet, starting at either 30' or half max depth in feet (whichever is greater). The Vytec doesn't start crediting anything as a safety stop until about 18' continuing up to about 12'. Anything 20' and below seems to penalize, based on the NDL it displays, as if you were still ongassing. If I were to dive it in computer mode I'd have to "fake" it out by still doing three minutes between 18' and 12' or it will most certainly complain and penalize repetitive dives. Regardless of how I got to that point.

One workaround for the Vytec is to put it in the RGBM50 mode, the other of course is to use it in gauge mode and depth average my tables, but I certainly don't advocate anyone else doing that.

 

[DivesWithTurtles]

IMO the key problem with Hill's ascents is NOT that they were smooth, but that they were linear. In other words, he was doing a constant speed of ascent rather than one that slowed as you get nearer to the surface.
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A smooth VARIABLE rate ascent or the approximation of that same VARIABLE rate ascent (becoming slower as one goes shallower) through a series of stops are pretty much equivalent.

Ok, I can dig that. And this is what Snowbear is teaching me also, yes?

But, also note this statement by Marroni, found here: "Lewis showed that the stop is in fact preferential to slowing the ascent rate. Thus, as indicated previously, a 5 min safety stop is much more effective than a reduced ascent rate..."

... What is amazing is that people are still recommending that style ascent --- the 30 second move + 30 second stop every 10' all the way to the surface that is being taught by some instructors has the same drawbacks as a smooth, continuous, linear/constant rate Hill-type ascent.

And that is why you advocated the dir-diver.com profile vs. the ad-hoc stuff being made up by some dir-f grads in the thread that you referenced previously.

My profile consists of 1 minute stops every 10 feet, starting at either 30' or half max depth in feet (whichever is greater). The Vytec doesn't start crediting anything as a safety stop until about 18' continuing up to about 12'. Anything 20' and below seems to penalize, based on the NDL it displays, as if you were still ongassing.

1. That is a linear ascent, a bad shape.
2. You are still on-gassing (in some tissues) as long as you are under pressure and the tissue has not reached saturation at that pressure.