Purchasing your first dive computer. A non-technical approach.

[scubadada]

I have a pet theory that tissue calculation model should be affected by non-mandatory safety stop as well, and that repeatedly skipping the optional but highly recommended safety stop should eventually result in higher calculated residual loading and shorter ndls. And that 'there is no penalty' does not mean you'll get the exact same ndls whether you skip the safety stops or not, it merely means you won't get locked out. ICBW and there's no feasible way to test it, so... whatever.

I've seen about 10 people complaining how suuntos cramp their style on scubaboard, and at least 5 times as many divers wearing zoops and vypers on actual dives.

You eliminate more nitrogen spending the 3 minutes on the surface than at 15 feet.

You make a safety stop to help ensure that your overall ascent rate is slowed and appropriate before surfacing. It does also provide surfacing a little farther from limit dictated by the decompression algorithm you are using.

 

[Joneill]

I have a pet theory that tissue calculation model should be affected by non-mandatory safety stop as well, and that repeatedly skipping the optional but highly recommended safety stop should eventually result in higher calculated residual loading and shorter ndls. And that 'there is no penalty' does not mean you'll get the exact same ndls whether you skip the safety stops or not, it merely means you won't get locked out. ICBW and there's no feasible way to test it, so... whatever.

The Shearwater tissue calculations, and subsequent dive NDL's, do factor your safety stops in. I would think most computers work this way?

The SW's won't add a separate "penalty" if you skip a safety stop. However, the extra time at depth/off-gassing to reduce your N2 loading is obvioulsy lost - so the calculations will leave you with higher residual N2 than if you had done the SS.

EDIT: After reading subsequent posts and researching more, I see that the SS is not about extra offgassing as you will off-gas faster at the surface. So it seems to be more about controlling speed of off-gassing and minimizing bubble formation/bubble size to lessen chances of DCS that could result from a rapid ascent straight to the surface. That's what's great about SB - it provides great inputs and makes you question everything - a good way to learn!

I've seen about 10 people complaining how suuntos cramp their style on scubaboard, and at least 5 times as many divers wearing zoops and vypers on actual dives.

Of course - they are cheap and simple. As others have stated, a lot (most?) rec divers are diving their computers and, in many cases, the dive profiles won't result in being "cramped". However, that does not mean they would not be cramped if they wanted to dive a somewhat deeper profile, esp after many repetitive dives.
Again, not bad computers, but I've seem more restrictive NDL's from buddy's Zoops after multiday, repetitive diving - based on profiles you you want to dive, that may or may not be somewhat limiting.

 

[dmaziuk]

You eliminate more nitrogen spending the 3 minutes on the surface than at 15 feet.

Brian R Morris seems to disagree. Of course, his product is not DSAT so he can't be right.

 

[KenGordon]

You miss my point. I was on a recreational dive boat - it's NDL diving, so deco stops are not really "allowed" if you want to keep diving with them (whether trained or not). Max dive time is set at 1 hour and you don't get to pick the sites or how long your SI is. I was not complaining about these things and still enjoyed these dives.

I know that NDL is affected by multiple days of repetitive "deeper" diving so I fully expected my NDL would be lower and made sure to monitor it to avoid a deco situation. I use the planner function on my Perdix to get a sense of NDL at expected max depth for the dive.

However, the actual dive usually unfolds a little differently - I may go a little deeper than predicted or stay at the deeper depths a little longer. Therefore, i would not want to be further NDL limited by a more conservative computer or one that might trigger the false ascent rate alarms due to flailing arms as was being discussed. That's all.

It is not that stops are not allowed. Staying too long is not allowed.

It is you that is doing the dive, the computer is only a guide. The 'keep within NDL' is to reduce the chances of you getting bent. It doesn't matter which computer you use if the profile is the same. Do the stops and surface with lower N2.

Exceeding ascent rates makes it tell you to do more stops. This is a good thing as you just increased the risk of a bend. It is only a minute though, hardly a big deal.

 

[scubadada]

Brian R Morris seems to disagree. Of course, his product is not DSAT so he can't be right.

Sorry @dmaziuk,

You can not change the law of physics.

Very best, Craig

 

[stuartv]

Brian R Morris seems to disagree. Of course, his product is not DSAT so he can't be right.

On the surface, your pN2 is 0.79 ATA.

At 15', you'd have to be on roughly 50% O2 to have the equivalent off-gassing.

 

[Joneill]

It is not that stops are not allowed. Staying too long is not allowed.

Really?? You're just mincing words. It's semantics, as staying too long = incurring deco obligations/stops which is not supposed to happen on dive boats running NDL dives with limits on max dive times. Ignoring NDL/incurring deco and ignoring max dive times is inconsiderate to the DM and the other divers on the boat (which typically has a schedule to keep).

It is you that is doing the dive, the computer is only a guide. The 'keep within NDL' is to reduce the chances of you getting bent. It doesn't matter which computer you use if the profile is the same. Do the stops and surface with lower N2.

It does matter. Different computers will "allow" you to dive a somewhat different profile while keeping you within NDL based on differences in algorithm and possible conservatism settings.

Exceeding ascent rates makes it tell you to do more stops. This is a good thing as you just increased the risk of a bend. It is only a minute though, hardly a big deal.

You do not increase the risk of a bend if the stop was triggered by a false ascent alarm - as was being discussed.

 

[KenGordon]

Really?? You're just mincing words. It's semantics, as staying too long = incurring deco obligations/stops which is not supposed to happen on dive boats running NDL dives with limits on max dive times. Ignoring NDL/incurring deco and ignoring max dive times is inconsiderate to the DM and the other divers on the boat (which typically has a schedule to keep).

It does matter. Different computers will "allow" you to dive a somewhat different profile while keeping you within NDL based on differences in algorithm and possible conservatism settings.
.

There is a limit on time. How you chose to spend that time is up to you. If you want to spend 5 minutes at 5m or go directly to the surface is your choice. In the dives you posted complaining of running out of NDL at 100ft you could have chosen to split the time differently, spent longer on the interesting part and then done the required stops. If the difference between brand X and brand Y is that brand X gives the stops and brand Y does not then really it does not matter as you will not actually be planning a direct ascent in any case.

What you are suggesting is that because the brand Y computer is happy about your longer profile then the boat ought to be happy.

Consider your GC dive. You ended it after 45 minutes with gas to spare because there was nothing to look at at the depths you could stay at without incurring stops. The way I would do that is plan a total time in the water, within the limits impose by the boat and split the bottom time between that and the stops. Within your 45 minutes you might have left the bottom 10 minutes later and still had 20 minutes to make the ascent. Exactly when to leave the bottom is subject to your actual profiles of the day. Once you start to plan based on a maximum time to surface you get many more ways to run your dive.

Also, use nitrox. At these depths you get 40% longer.

 

[Diving Dubai]

Hi @Diving Dubai

I don't know about the other current Suunto computers, but the Eon Steel you dive nearly matches DSAT when dived on personal level setting -2, "more aggressive"

I was being a little factious with my post, as it's usual for people to keep quoting that Suunto's are conservative.

Yes I understood that the Eon on -2 was close to DSAT, as is the DX as they both use the Fused RGBM model. I rarely run mine on -2 as for differing reasons I prefer some addition headroom.

I've just been given the use of a Perdix, and a Suunto Nova, which I'm going to wear alongside with my Eon for a few dives - purely so I can find which conservatism settings I need to apply to match them roughly. This is purely of interest so that I can "calibrate my Eon to have similar NDL's to the others - thus when leading dives I'm not a million miles away.

I'll of course be interested to see if the Perdix lives up to the hype for my diving, I'm considering an additional computer and my choice is between the Perdix and the OSTC 4. I'll report back my none scientific findings

Safe diving

 

[gfaith]

@Joneill

You do not increase the risk of a bend if the stop was triggered by a false - as was being discussed.

I am going to challenge the "flailing arms appearing to be causing fast ascent and causing a Mandatory Stop".. I would believe a warning beep for that fast arm movement, but not a Mandatory Stop. If you can provide proof I will accept it.. I can and will test this during some future dives.. arm flailing/waving and all with both Viper Air and backup Zoop. My buddy will think I'm crazy.