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What I learned today...

Discussion in 'General Scuba Diving' started by Wibble, Apr 15, 2019.

  1. jb2cool

    jb2cool Moderator
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    If you think the Suunto is giving you too much deco you can adjust the aggressiveness of the algorithm. Have you considered that maybe the Shearwater wasn’t giving enough deco? What were it’s settings.

    I’m no Suunto fanboy but they do work for the majority of diving, sure once you start getting into deco territory other things may work better to your liking but there in nothing inherently wrong with Suunto. It’s when you have mixed teams with divers using different algorithms where some of these weaknesses are exposed, if you were both diving Suunto then you may have been ok with it.
     
  2. John F

    John F Active Member

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    I do agree with the last few comments, I did have my Eon set to most aggressive setting, as other dives had shown a big difference between me and my buddy.
    I don’t really have a problem with the suunto, it’s just a bit frustrating when there is such a difference between mine and my buddy’s.
    I assume my buddy’s Shearwater was working correctly as if he had missed 14 minutes of deco, he would probably know about it.
     
  3. Wibble

    Wibble Fish don't talk
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    The problem with the Suunto computers is the proprietary algorithm they use. This is fine for recreational diving but differs too widely from the "normal" Buhlmann algorithm which most** tech divers use (and therefore tested and trusted by many many more dives than Suunto's algorithm).

    Other issue is the Suunto user interface. Shearwater's are incredibly easy to use and the display amazingly clear with all the information available on one screen.

    The issue with your "personal attitude to decompression" is almost implying that if you choose -2, the most aggressive, you're being cavalier. The reality is that even at this setting it still would keep one down longer than a dive done with Buhlmann 50:80.

    Oh, and Suunto's lie. Example MOD (max op. depth) which is simply Dose over Mix e.g. 28% is 1.4/0.28 = 5ATA = 40m, but Suunto subtract 2% for some made up BS reason.


    So @John F, get a Shearwater (or OSTC, or any other Buhlmann supporting computer). Several of us on here dive them and I've not heard of many (any?) complaints. There must be a reason that almost all rebreather manufacturers have opted for Shearwater computers.

    ** Not all tech divers, but most will use Buhlmann. Other algorithms are available including ratio deco.
     
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  4. Harvey-NG

    Harvey-NG Member

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    The faux tec Suunto computers tend to baby the user a bit, by adding extra unexpected deep stops and occasionally longer deco than planned. They also as Wibble pointed out have a bizarre way of calculating the gas MOD which is irritating, but all of this is done in the name of safety. The benefit of using a Shearwater is that it gives you all the decompression data you need to make a safe ascent without trying to do it for you (other computers are available but I don't have any experience with them.)
     
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  5. Harvey-NG

    Harvey-NG Member

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    But hey, they do make lovely bottom timers.
     
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  6. Wibble

    Wibble Fish don't talk
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    > Suunto’s conservatism

    Not sure about their strategy. Shirley it’s down to the diver to understand what’s going on and the computer to give them the info to support that?

    I remember some time ago people diving with Scubapro computers which show the seconds for “safety stops” and the divers blindly following them with the zeal of being threatened with being bent. One (good) thing with the Shearwater is it doesn’t show seconds, just quarters of a minute.

    And, of course, deep stops aren’t exactly the flavour of the month now as they’re under fire for having dubious utility.

    Don’t the latest Suuntos support Buhlmann?
     
  7. JasonP

    JasonP Active Member

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    They 'subtract 2%' because they're calibrated for salt water which is about 2% denser. So at the same depth in the sea, they will show a shallower and more accurate depth than a computer calibrated for fresh water.

    This has no effect of ppO2 or deco calculations as these use the pressure rather than the depth which is only really displayed to the user.

    Sent from my LG-H990 using Tapatalk
     
  8. Wibble

    Wibble Fish don't talk
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    That's the best description I've heard for it and makes absolute sense. Suunto told me (I wrote an email to them asking) that it was for "additional conservatism".

    However, subtracting 2% for seawater is such a moot augment: it's pressure we care about not depth. At 5 bar you've the equivalent(ish) of 40m over your head. Of course, if you took a tape measure you'd find that it's slightly deeper or shallower depending on the density of the water. But nobody does that!

    Your deco obligation and MOD (Max Operating Depth) are pressure dependent - it's Bar not MSW nor MFW (Metres Sea/Fresh Water).

    Personally I think it's something to do with the Yanks. They've that amazingly complex set of calculations for gas volumes and MOD that they seem to think that adding another tweak for water density is somehow good and acceptable. That's what you get for using cubits and flagons for your measurement system. Reckon that some pillock at Suunto added it to their dive computer as it's "more tech".

    Thankfully the people at Shearwater are pragmatic.
     
  9. JasonP

    JasonP Active Member

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    You're still not getting it. At 5 bar, you're shallower than 40m in sea water. That's why the Suunto shows your MOD as shallower than you'd expect. Computers calibrated for fresh water will give you the MOD you expect, but display a depth that's greater than your actual depth.

    I'd be surprised if there isn't an option on Shearwater to adjust for fresh or sea water.
     
  10. Wibble

    Wibble Fish don't talk
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    OK, I'd rather measure "depth" as pressure of water in Bar. How deep I am isn't relevant; how much pressure is on me is very important.

    The guideline depth for the Persiania this weekend is 45m. The exact depth will vary, probably not deeper. I won't be taking the density of the water into any planning calculations, just using 1 Bar = 10m, so 5.5 Bar. Therefore the gas will have no more O2 than 1.4/5.5 = 0.25 = 25%.

    The Suunto has to have all gas PPO2 set to 1.6 because the damn thing can't understand normal calculations.
     
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  11. ScottWarr

    ScottWarr New Member

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    Love your scientific mind Wibble!
     
  12. Tribal Chestnut

    Tribal Chestnut Well-Known Member
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    How much did he pay you?
     
  13. Iain Denham

    Iain Denham Active Member

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    It does
     
  14. Wibble

    Wibble Fish don't talk
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    Why would one *ever* care about the water density when the *only* thing that affects decompression is pressure (as in for identical mixes). Absolute depth is an elephant.
     
  15. John F

    John F Active Member

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    Change of subject, I have found a very good documentary on BBC I player called “ last breath”. About a saturation dive in the north see that sent very wrong. I very much recommend it.
    John.
     
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  16. splinter

    splinter Active Member

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    I watched that the other day. Well worth watching.
     
  17. Wibble

    Wibble Fish don't talk
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    Great documentary short series on BBC 2 about cave diving in Mexico last night.
    "Undiscovered Worlds with Steve Backshall"

    Interesting and odd that he's so inexperienced (for someone with "thousands" of dives)
     
  18. Graysyid

    Graysyid Active Member

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    I watched it the other week with the wife, she couldn't watch all of it as she isn't a fan of deep water
     
  19. Tribal Chestnut

    Tribal Chestnut Well-Known Member
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    Not seen it, but what do you mean by inexperienced? He only did full cave last year so I imagine that was to enable the filming to take place.
     
  20. Chimpus

    Chimpus Member

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    Thanks for that.
    Watched it this evening. Gripping stuff.
     

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