Question about dive computers

[KenGordon]

Hi @KenGordon

I noticed that your Suunto decompression profile looks very different than that when running 50/80, with significantly less time at deeper stops and more time at the last stop. The Suunto profile actually looks most like 75/75, though the Buhlmann profile still has more time at the deeper stops. I find that quite interesting. All 3 profiles have nearly the same runtime and total deco time.
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75/75 just adds an extra minute at 3m. There is still a stop at 12 and more time at 9 and 6. The Suuntos want to get shallow fast. You know the opposite of what people say about bubble models. Maybe that is because it isn't a bubble model...

Actually these profiles are all identical within the parameters of actual diving. Look at the real dive. It isn't much like any plan you are going to put into a planner. Unless the wreck is flat you're not going to spend the entire dive at the maximum depth.

With some fiddling 100/80 vaguely comes out like the zoop but is a bit short at 9 and long at 6. The reason is that the ratio of the compartments will be different and the actual choices of compartment will be different. It feels like the fast tissues are not the limiting factor for surfacing and those that are have lower limits than ZHL16C.

 

[scubadada]

Hi Ken,

Say what you will, 75/75 has 4 minutes more below 3m than the Suunto profile. This is a clean 1st dive, the real difference between Suunto and Buhlmann is 2nd and subsequent dives. Feel free to go ahead and model these, the differences show up in the ScubaLab no stop testing My Oceanic computer runs something like 95/95, I've not had a stop below 10 ft up to 14 minutes

If you plan multiple dives on the Suunto, does it take into effect the short SIs, quick ascents, sawtooth profiles, reverse profiles, etc., that may be part of real dives? I know nothing about the Suunto planning function, the curious would like to know.

 

[KenGordon]

I can plan a dive in subsurface, write it down on a slate, and dive it with my Leo. I would not be comfortable doing that because nothing in the available documentation tells me a) whether Leo will get its knickers in a twist if I set it to dive (as opposed to gauge) mode for it, nor b) how it would react if I have to deviate from the plan for any reason. Presumably it won't compute me a decade of deco, but the fine manual is completely silent on the subject.

If you know how zoop would behave and your planner matches its programming, then sure, do decompression dives on a zoop in dive mode. I still doubt its calculated deco schedule will match those of Eons, but hey, it's your deco.

There is a different setting for planning for the DX/Eon, and for the Helo2/D9tx etc. Also for the personal settings and altitude, last stop etc. As when using using a GF planner you need the settings to match the computer. At least in this case you know the same company was involved with both parts and might reasonably expect the people responsible to talk to each other.

 

[KenGordon]

Hi Ken,

Say what you will, 75/75 has 4 minutes more below 3m than the Suunto profile. This is a clean 1st dive, the real difference between Suunto and Buhlmann is 2nd and subsequent dives. Feel free to go ahead and model these, the differences show up in the ScubaLab no stop testing My Oceanic computer runs something like 95/95, I've not had a stop below 10 ft up to 14 minutes

I was comparing 75/75 with 50/80 with my one minute difference point.

If you plan multiple dives on the Suunto, does it take into effect the short SIs, quick ascents, sawtooth profiles, reverse profiles, etc., that may be part of real dives? I know nothing about the Suunto planning function, the curious would like to know.

Other than a short surface interval (SI), those things just add extra safety stop time. Ignore that extra minute and it shortens the following dive's NDL. The planner doesn't have an 'ignore what you are telling me setting'. On the other hand what it is doing in the water is minor and in the direction of safety. You plan a dive to make sure you have enough gas. Having a shorter NDL than expected doesn't introduce a risk of running out of gas. Having an extra minute of optional safety stop doesn't introduce a risk of running out of gas.

A short SI will be accounted for by any computer. During the SI the computer model is off gassing. Less gas will be got rid off with a shorter one, especially for slower compartments. If a given model puts less emphasis on faster compartments than slower ones that will make a bigger difference to the subsequent no stop times.

Indulging you I planned a 40 minute 25m dive 59, 60 and 61 minutes following the 44m Markgraf dive. This would be a cruiser such as the Karlsuhe SMS Karlsruhe Wreck Intro | Scapa Flow Wrecks

They all come out with 30 minutes at 3. A 58 minute SI gives 31 minutes at 3. a 62 minute SI gives a 29 minute stop.

Of course nobody would actually do such a short SI. It takes time to refill 12 twinsets and there is lunch and cake to eat. Ah, "what about rebreather divers? No fills for them." you ask. Yes. They will get all the cake and could get in an extra dive so long as they can get the skipper to move the boat. The TTS of the first dive is 20 minutes shorter and the second dive is practically no stop. So the solution for people who want their cake and eat it is to stop messing about with aggressive computers and dive a proper (variable) mix. Or for the same ascent time you could have 44 minutes on the wreck first rather than 23 and an hour rather than 39 minutes on the second (still with 60 minute SI). With a more reasonable 3 hour SI that comes down to 12 minutes of stops and you'd still be at the pub before opening time.

So, if you are obsessed with doing a slightly longer dive, give up with Oceanic, DSAT, GF and ZHL16C, then FOR THE SAME MONEY buy an old classic Inspiration and do it properly.

 

[KenGordon]

This thread may be getting a little deep in the weeds for a recently certified diver. I'd like to offer to the OP my 2 cents about disappointing support from some DC manufacturers. I had an Aeris Elite T 3 which I loved for its simple intuitive display, ease of switching to Nitrox. It did fail about every 2years, and for something like $100, the factory sent me a refurbished unit. The company no longer supports this unit. I later bought an expensive Liquivision Lynx thinking I would like the bright display. But I hated the toy like cosmetics of it and quickly sold it. The friend who bought it from me said it failed and the company is no longer supporting it. (He's still a friend, though.). Two friends, both Instructors have the very expensive Atomic Cobalt. Neither one can keep the units in service. One asked me to take a photo of his blank screen in the middle of a dive so the company would believe him that it failed. The other friend said his lights up with a lag, something like ten minutes after getting wet. The danger there is that it apparently also doesn't track his gas consumption for the first ten minutes.

I currently have a Perdix 2 and a Petrel. Knock on wood, performance and reliability are perfect. There are a lot of supporters of Shearwater on this board and based on my personal experience, I'm one of them.They may be too pricey and over engineered for a new diver but something to think about.

This is a good point. History has a fair few DC companies that didn't really perform. Some of the products were very cool too.

As regards the weeds. Much is said on this forum by people without direct experience of the products they are talking about. If people took SB literally they'd all have Petrels set to 45/95, an SPG and a stand alone compass.

 

[dmaziuk]

As regards the weeds. Much is said on this forum by people without direct experience of the products they are talking about.

Oy, I resemble that remark. But i'm trainable, e.g. now I know Suunto planner has a knob for cutting plans for Zoops.

 

[scubadada]

Hi @KenGordon

So your 1st dive looks like 75/75, your second dive looks more like 55-60/55-60 to generate 30 min at 10 ft. I guess that's what Suunto RGBM does for you.

 

[KenGordon]

Hi @KenGordon

So your 1st dive looks like 75/75, your second dive looks more like 55-60/55-60 to generate 30 min at 10 ft. I guess that's what Suunto RGBM does for you.

75/75 doesn't let a diver go directly to 9m for that dive. There are no GF numbers which match. GF applies equally to each compartment. The two models have a different number of compartments, different compartment half times and then very probably different m-values for similar half time compartments. The Suunto may not use exponential off gassing (I'd need to check that - I could easily be wrong).

I picked an hour because it is often suggested that there is a hard rule in place in Suunto RGBM regarding the SI.

Eventually, after 2h30 (a reasonable time for fills, lunch) the Suunto is inline with a 50/80 profile again.

Looking at the last time I was doing 4 dives a day my minimum SI was 1.45, and that was before a shallow night dive. The more serious dives had 3 hour SIs.

If the second dive was only 19m then it is no stop for both the Suunto and the 50/80 profile. Is that too terrible? A long SI is good practice. If your boat will not give you that then find another boat.

 

[scubadada]

Hi @KenGordon

Your dive profiles are different than the ones we do in south Florida. We often do 4 dives per day. 1st 2 often have a SI of about 45 minutes, 2 hours over lunch then another 45 min between dive 3 and 4. Not like your deep wrecks, we have more flexibility between the wrecks and reefs.

 

[KenGordon]

Hi @KenGordon

Your dive profiles are different than the ones we do in south Florida. We often do 4 dives per day. 1st 2 often have a SI of about 45 minutes, 2 hours over lunch then another 45 min between dive 3 and 4. Not like your deep wrecks, we have more flexibility between the wrecks and reefs.

I looked back and quoted my SI for four dive days, those were Komodo, the Red Sea is similar.
With four one hour dives there is still time for three two hour SIs. If those dives are at all deep then it looks like a bad idea to me to only be leaving 45 minutes. Why do you do that? For the boat’s convinience? Are you going far off? How long and how deep are those dives?