Are Suunto Zoops super conservative?

[scubadada]

Meh. I don't know what it's actually showing: 6 minutes at 30 metres, then 3 metre ascent in 2 minutes, then 3 metre ascent in 4 minutes, then 6 metre ascent in 14 minutes, then 6 metre ascent in 16 minutes and at that point then NDLs are between 15 minutes and one hour? If that's what it is, SFW? What happens after I spend 4 minutes at 12 metres? -- I'm pretty sure I won't be OOG yet on AL80 and I'm also pretty sure I won't have the gas to spend another hour at that depth. So what does this pretty picture actually mean to me?

It shows you that if you push the NDLs, more toward their limits at depth, you will have more time underwater with a liberal computer that you will with a conservative computer, what did you think?

 

[Umuntu]

I was just reading the recently reading the British Sub Aqua Club (BSAC) National Diving Committee Diving Incidents Report 2017. The following quote from Page 4 caught my attention [emphasis added]

QUOTE

Decompression incidents​

The BSAC database contains 56 reports of ‘DCI’ incidents in the 2017 incident year, some of which involved more than one casualty. An analysis of the causal factors associated with the 56 incidents reported in 2017 indicates the following major features:-​

1. 
   45% involved diving to deeper than 30m
   41% were within the limits of tables or computers
   41% involved repeat diving
   11% involved rapid ascents
   7% involved missed decompression stops
   
   Some cases involved more than one of these factors.
   Given that 41% of DCI cases arose from dives reported to be within decompression limits, divers should be alert for DCI symptoms arising from any dive.

UNQUOTE

Do any other Diving organisations in other countries compile Incident Reports ?

 

[rsingler]

So what does this pretty picture actually mean to me?

Well, I just posted it to show that there are clearly measurable differences in the approach to NDL's among the various algorithms. At common rec depths (40-60') and common dive times (45 min), the differences among brands and their algorithms are easily seen.
Now take those varying approaches and apply them over 15-30 repetitive dives on someone's dream vacation week and one of two things MIGHT happen: 1) two buddies with different computers might get very frustrated as the more conservative one limits the pair on the fourth or fifth day; or 2) a diver (like a lot of folks in this thread who suggest "tweaks" to make their computer read like they want it to) might end up with an "undeserved" hit (?) because the liberal algorithm he naively picked, plus edge-of-the-envelope diving, left him with more N2 than his body could handle during an ascent. If he knew in advance that HIS algorithm was very liberal, he might (or might not) CHOOSE to adjust his risk profile.

I don't know what it means.
It means computers are different.
It means choose your poison, but realize what you're choosing.

A lot of divers just "buy a computer".
Some divers complain that their computer limits out too early. Well, this little picture suggests why: different algorithms. It may help somebody choose "more liberal" or "more conservative".

That's all.

 

[KenGordon]

Why don't you dive with me? You can see for yourself. I know what they are when I look at them at 99'. I also know I have a big difference when I come back up to 60'.

Ok, get yourself on a plane and I’ll take you for a dive.

On a less flippant note, as maybe you don’t really understand, the Suunto NDL for 30m on 32% is 28 minutes (17 for air). Multideco gives 6 minutes of stops for 28 minutes at 30for GF100/100. Your Perdix would certainly give more. So the advice you were given could have you missing a lot of stops.

Using a richer mix to decrease conservatism is a bad plan. On the face of it it seems ok, pretend you got less gas, seems easy. However the equations are not linear, so over time the error is hard to guess. Also it will have you OFF gas faster, so a multilevel dive might be REALLY wrong as the computer starts giving credit when it should still be adding penalty. It doesn’t matter how big the limit is if you fool the computer that you are walking away from it.

 

[rongoodman]

But my experience was it took 5 min to complete a 3 min safety stop because of this. And our swells were not that great. My oceanic 2.0 restarts if there is a significant difference at safety stop but that is only on extreme conditions or when I’m doing a shallow dive finish. Just not a fan. Lastly, I like my safety stop at 20 feet and we couldn’t figure out how to change that.

Is there some reason to just not complete your safety stop when you think it's time, rather than wait for your computer to agree? Will it somehow penalize you for doing so?

 

[rsingler]

Is there some reason to just not complete your safety stop when you think it's time, rather than wait for your computer to agree? Will it somehow penalize you for doing so?

If by "complete your safety stop when you think it's time" you mean surface after three minutes even if the computer clock keeps restarting, then yes, it's probably just fine to surface. Your computer won't penalize you for skipping a safety stop. Since we are doing No Stop Diving, you theoretically don't have to do a safety stop at all, and computers recognize this.
That said, there's something else to consider regarding @myshadeofred 's post. @boulderjohn explained why her computer kept resetting (crossing below the 20' threshold that restarts the safety stop clock). I have heard divers say that since there's no safety stop required for dives above 30', if you complete your three minutes anywhere from 1-30' you're fine.
With repetitive dives that push the envelope, that clearly isn't the case. Inspection of common decompression profiles for dives that exceed the NDL clearly show stops at 20', and then even longer stops at 10'. Doing a safety stop at 20 feet ONLY, after a long repetitive dive, is ignoring your fastest compartment. But 15' was a compromise choice when the tables were designed anyway, so it's generally not an issue. Again, we are doing No Stop Diving.
So my recommendation is to choose your computer (see discussion of differing algorithms above), adjust it for your desired conservatism if possible, and then follow its recommendation. If you make your own decisions based on gut feeling, while your computer is integrating 16 theoretical compartments and suggesting a different ascent, you can't call your case of the skin crawls an "undeserved" hit.

My 2 cents

 

[boulderjohn]

@boulderjohn explained why her computer kept resetting (crossing below the 20' threshold that restarts the safety stop clock).

To be accurate, I said that with a Suunto, when you go out of its safety stop range briefly, it stops counting the safety stop. It does not fully reset, and it will go back to where it was in the stop before you left that zone.

If you leave the zone for a longer amount of time (and I have no idea what that is), it will indeed start over. Let's say you are doing one of the cavern dives in Mexico in which you ascend to a safety stop depth halfway through the dive and then descend below it for the rest of the dive. When you go above 20 feet, it will start a safety stop countdown, but after you have been below it again for a while, it goes back to dive mode. (To be perfectly honest, I am not sure I ever did that when I owned a Suunto, so that last statement is something of a guess.)

 

[dmaziuk]

what did you think?

I thought if I had the gas and burning desire to overstay my computer's NDL, I'd just live dangerously and turn my highly recommended safety stop into a non-optional perilty stop: the whole point of wearing the computer is it will compute it for me. As long as The Scuba Police is not around.

 

[scubadada]

I thought if I had the gas and burning desire to overstay my computer's NDL, I'd just live dangerously and turn my highly recommended safety stop into a non-optional perilty stop: the whole point of wearing the computer is it will compute it for me. As long as The Scuba Police is not around.

So...Your profile will just be different than mine. I will stay at depth longer for any comparative shallow stops, whether it's a safety stop or light deco.

 

[dmaziuk]

So...Your profile will just be different than mine. I will stay at depth longer for any comparative shallow stops, whether it's a safety stop or light deco.

And that's going to happen because..?

Sorry, I tend to be obtuse like that. Like, "bloody zoop made us spend 5 minutes at safety stop instead of 3" -- that's a bad thing now? What, you were late for the flight? (If the complaint is that a couple of teenagers couldn't stand still during the stop, then I, as a former teenager myself, am willing to bet that zoop had nothing to do with it.)

You want to stay longer than me at depth, be my guest. What does the colourful infografic has to do with it?

I don't think I'll ever get it.