Dive Computer No Deco Computations Question

[Jai Bar]

I'm not sure this is today's understanding. Also, the fact that they are both models does NOT mean they are equally flawed. In addition to the RGBM aspects of the Suunto, it also has its own extra "safety factors" it puts into play (for example that less than 45 min SI is worthy of a special penalty on the NDL of the next dive) plus other unjustified by data penalties, in addition to just plain going silent for 48h under some conditions. Yes, the Suunto is probably safe, in the same sense as not diving at all will keep you safe. It is demonstrably unnecessary nannyism.

Unjustified by who? You? Nannyism? Have you ever tried to simulate microbubble nucleation kernels? I get it, the compartment model is concept easier to understand, whereas bubble dynamics with varying boundary conditions is more complex material, so whatever one does not understands is almost automatically labeled as "Unjustified", " Voodoo" and so on.

I have been diving with this or that Suunto for decades and never felt that it somehow is nannying me, punishing or impeding my dives with over conservationism. How do I know that? Because in many diving liveaboards we usually are the first in last out in all dives, so Suunto's RGBM cant be that bad (plus, I am quite familiar with bubble models, hence don't have an so much inherent mistrust of the unknown), but perhaps me and my buddy do not conduct aggressive dive profiles.

Anyways, Suunto's liquid crystal screens began to be more hard for me to read over the years, and we also started night diving frequently so added Shearwater Peregrine on my wrist- because of the larger, illuminated display is much much easier to read.

Now, being the geek physicist that I am, couldn't pass over the opportunity to compare them hand by hand (literally), I use SW as primary and have yet to find a scenario in which the old Vyper penalizes me or turns to bottom timer.. But nowadays I do relaxed dives, usually don't go below 30m and begin multilevel ascent at least 5-7 minutes before NDL. And I seldom do.less than 2-2.5 hours surface intervals, so less chances of what one may call "Unjustified penalty"...

 

[Blackcrusader]

Thank you all for your responses. From what I gather collectively the Sunnto software and algorithm seems to have some limitations and flaws. However, you have to honor the most conservative of the two.

With that being said, a dive computer is an expensive and major purchase. Some of your nicer and higher recommended models (Shearwater Teric for example) run over $1,100. How many divers out there are really spending the money to buy another expensive second computer to use as a backup? I feel like if you buy a “cheap” computer as a backup then you pay the price like I am with my Suunto.

When I dive I often compare NDL times with guides on dives. They mostly use Suunto and they are aware my NDL times on my Perdix are far long than on the Suunto. One guide would use one DC on first dive, a different DC on second dive, switch back to first DC for third dive so he had longer NDL times. I use a Perdix AI with no air transmitter.

My back up is my Digital Cressi SPG as it gives me depth time air water temp and previous dives information. Neither my Perdix or Cressi can lock me out. lol Cressi does not give you NDL time.

The new Peregrines are closer to US$500 half the cost of a Teric. If I wanted get another backup to my Perdix it would be another Perdix or a Peregrine.

 

[Blackcrusader]

Yes, the Suunto is probably safe, in the same sense as not diving at all will keep you safe. It is demonstrably unnecessary nannyism.

Yes. I had times using my SUUNTO where if you did a safety stop time on a reef you were taking photos of if you dropped to say 8m the Sunnto would then show 9 mins for the next 5m safety stop. lol Mine the pressure sensor wnet kaput.

Never been so happy than diving with my Perdix day or night dives or low vis dives where I can see it easily whereas other people cannot see their DC displays.

Sunnto nannyied me to death lol

 

[runsongas]

@Tassie_Rohan mares/scubapro will still lock out for a violation. garmin does it also by default but allows for it to be toggled off at least.

 

[clownfishsydney]

When you say the Shearwater and Garmin run the same algorithm do you find the NCL times the same on both computers all the time?

I have these and they are always within a minute or two of each other.

 

[Belzelbub]

When you say the Shearwater and Garmin run the same algorithm do you find the NCL times the same on both computers all the time?

Yes. Very close. I've never seen more than a minute difference on NDL. And no more than a 1% difference on SurfGF. I wear one on my left wrist and one on. my right, so those differences are easily justifiable.

 

[tursiops]

Unjustified by who? You? Nannyism? Have you ever tried to simulate microbubble nucleation kernels? I get it, the compartment model is concept easier to understand, whereas bubble dynamics with varying boundary conditions is more complex material, so whatever one does not understands is almost automatically labeled as "Unjustified", " Voodoo" and so on.

I have been diving with this or that Suunto for decades and never felt that it somehow is nannying me, punishing or impeding my dives with over conservationism. How do I know that? Because in many diving liveaboards we usually are the first in last out in all dives, so Suunto's RGBM cant be that bad (plus, I am quite familiar with bubble models, hence don't have an so much inherent mistrust of the unknown), but perhaps me and my buddy do not conduct aggressive dive profiles.

Anyways, Suunto's liquid crystal screens began to be more hard for me to read over the years, and we also started night diving frequently so added Shearwater Peregrine on my wrist- because of the larger, illuminated display is much much easier to read.

Now, being the geek physicist that I am, couldn't pass over the opportunity to compare them hand by hand (literally), I use SW as primary and have yet to find a scenario in which the old Vyper penalizes me or turns to bottom timer.. But nowadays I do relaxed dives, usually don't go below 30m and begin multilevel ascent at least 5-7 minutes before NDL. And I seldom do.less than 2-2.5 hours surface intervals, so less chances of what one may call "Unjustified penalty"...

Many people like Suuntos, even though they do things like add a percentage point to whatever O2 percentage you enter...just to make sure, right? And penalizing one for diving deeper on a repetitive dive than on the preceding dive....which was discredited a quarter-century ago.

 

[Jai Bar]

Yes. I had times using my SUUNTO where if you did a safety stop time on a reef you were taking photos of if you dropped to say 8m the Sunnto would then show 9 mins for the next 5m safety stop. lol Mine the pressure sensor wnet kaput.

Never been so happy than diving with my Perdix day or night dives or low vis dives where I can see it easily whereas other people cannot see their DC displays.

Sunnto nannyied me to death lol

You may have misunderstood the reverse profile thing. Of course, as long as you stick to no decompression limits there is no evidence of additional risk by diving the first dive shallower.

There is no "penalty" involved in reverse profile diving, as long as you dive according to the tables or computer.

However, bear in mind that reverse profile may mean a shorter bottom time (again- if you stick to ND limits), and many divers think this is a penalty introduced by some shady algorithm or company lawyers who force to add penalties to mitigate risk and lawsuits.

Nope, the NDL calculated by Haldanean-based models (such as Buhlmann) doesn't care if you dive shallow or deeper first. At the end of the dive you surface with whatever nitrogen saturation levels, which gradually decrease during the surface interval. When you enter the second (or third or whatever) the new ND limits are updated. And you will see that reverse profile will result in shorter NDL for repetitive dives.

Now, most poeple may have not noticed this because they use computers and multilevel dives. But if you try square profiles- like classical table dives- you will notice that reverse profile results in shorter bottom time. For a recreational diver who wants to have fun underwater, this can be considered a punishment. For me it is, at least. When I used to dive tables, we planned the diving sites according to depths and did square profiles. With computer, we do multilevel and don't care anymore if it means a couple of minutes less at max depth (e.g. 30m) you ascend a little bit and NDL is updated on the fly and no one almost cares you can still enjoy a prolonged dive.

 

[tursiops]

You may have misunderstood the reverse profile thing. Of course, as long as you stick to no decompression limits there is no evidence of additional risk by diving the first dive shallower.

There is no "penalty" involved in reverse profile diving, as long as you dive according to the tables or computer.

However, bear in mind that reverse profile may mean a shorter bottom time (again- if you stick to ND limits), and many divers think this is a penalty introduced by some shady algorithm or company lawyers who force to add penalties to mitigate risk and lawsuits.

Nope, the NDL calculated by Haldanean-based models (such as Buhlmann) doesn't care if you dive shallow or deeper first. At the end of the dive you surface with whatever nitrogen saturation levels, which gradually decrease during the surface interval. When you enter the second (or third or whatever) the new ND limits are updated. And you will see that reverse profile will result in shorter NDL for repetitive dives.​

Now, most poeple may have not noticed this because they use computers and multilevel dives. But if you try square profiles- like classical table dives- you will notice that reverse profile results in shorter bottom time. For a recreational diver who wants to have fun underwater, this can be considered a punishment. For me it is, at least. When I used to dive tables, we planned the diving sites according to depths and did square profiles. With computer, we do multilevel and don't care anymore if it means a couple of minutes less at max depth (e.g. 30m) you ascend a little bit and NDL is updated on the fly and no one almost cares you can still enjoy a prolonged dive.

Perhaps you should look a little deeper into reverse profiles and what Suunto does. The penalties show up on the third dive, according to Suunto.

"So if you first make a shallow dive and after that a deep dive, we penalize the third dive if the surface interval is short."​

Citation: p177 of this document: Info - Reverse Dive Profiles Workshop, 2000​

​

 

[rongoodman]

I was quite surprised on my recent trip on the T&C Aggressor to hear the DMs making a big deal about avoiding reverse profiles. I didn't think that was a thing anymore.