Garmin MK2i for Rebreather Diving a KISS

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PepeUSMC

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I absolutely love my Garmin MK2i computer and use it daily for surface activities and love it for my open circuit diving. I have absolutely zero rebreather experience but I am interested in a rebreather sometime soon and have been leaning towards the KISS Spirit mCCR. I am the kind of guy who researches everything for hours and hours and reads hundreds of reviews before making a choice. So I realize that the Petrel (or NERD) is pretty much the standard computer for rebreather diving.....

My question is.....the Garmin MK2i has a rebreather menu and CCR setting, it allows inputting a high and low limit Partial O2 pressure etc. With a mCCR like the kiss can I still use my MK2i as my primary computer and as my decompression monitor etc. and just have a HUD that show the loop ppO2 for the rebreather and as long I as I keep my garmin apprised of my loop gas mix,.... is it sufficient? Any downsides?

Has anyone used the Garmin MK2i for CCR diving?

Thanks for the help in advance!
 

grantctobin

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Could you dive a (Spirit, Meg, SW, etc) with only a HUD wired into the computer? Yes. In fact, old Classics came only with a triple PO2 monitor. You would then dive fixed PO2 tables, and later, fixed PPO2 external computers with it.

Should you? Probably not. I don't think any instructor is going to permit you to do so during your education, and for a few reasons. Perhaps the most important is only having a HUD would not permit you to see cell mV values. I actually don't know if Mike/Kim will sell you one.

Let's say you could go this path and you're diving. If your MK2i dies, you're left with only the ability to monitor your PO2 and little else. Definitely wouldn't recommend this, especially with a decompression obligation. As such, now you add an additional backup computer. A Perdix AI or an Teric or MK2i are not very different in price from a Petrel 2 EXT.

However, there is use for your Garmin MK2i. It would become your backup computer. For experienced CCR divers, the difference in TTS and decompression plan between a fixed PPO2 backup and a live monitor is very small, even in long (4+ hour) dives.

So what are your options with a Spirit?
1) Hardwired Petrel 2
2) 4-Pin Petrel 2 or 4-Pin Nerd2
3) Fischer Petrel 2 or Fischer Nerd 2 (please don't do this)
4) Freedom (@tbone1004 has more experience with these than I do)
5) Petrel2 + Nerd2
6) Petrel2 or Nerd2 + HUD

You'll get varying opinions. Most people adore their NERD2. I ditched mine because I can't see it in a whiteout but can see my HUD light. Do you need dual monitoring? Early CCR monitoring and electronics were far more failure prone that current Shearwater technology. I'd argue that it depends on how intense your diving is getting. If you're on expedition abroad, on a once in a lifetime trip, or a few miles back in a cave, I'd argue for dual monitoring. That said, Mike Young's Spirit has a single hardwired Petrel 2. Edd Sorensen's sidewinder has only a Petrel 2.

So if you go dual monitoring, how should it be done? The Sidewinder and Spirit heads are rather small and splitters vary in function and reliability. Both KISS and Fathom sell a board that can be installed rather than splitters.

If you go with a HUD and not a NERD2, I'd recommend looking at the Fathom one. Shearwater, N@90, and Fathom I think are your only analog options. A hardwired or 4-Pin Petrel 2, a hardwired Fathom HUD, and a backup Garmin MK2i on your wrist will happily let you do anything a Spirit can do.
 

Jeremy Williams

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It’s not a great plan, and that’s not particular to the Garmin. It’s no different if you had a Shearwater Perdix or Teric as well…

The primary downside is that your computer is only as good as the information you give it. Without the ability to read the cells in your rebreather, it’ll never know what the ppO2 is in your loop. The computer will assume that what you’ve told it is correct and it’ll be up to you to maintain the set point that you have told your computer that you’ll be running. This may be a reasonable backup strategy (although I have two wired computers), but IMO not a reasonable primary strategy. Failing to maintain the set point with a reasonable degree of accuracy is going to inevitably end in DCS. Maintaining your set point from the blink HUD as a primary mode of operation is possible but is going to take more of your attention than you really want (despite what others may say).

The other thing that’s super insidious about the approach you are suggesting is that you’ll never get to see how far off you are! I did some CCR dives with one wired computer and a second computer on the fixed set point. The deco profile was quite different. I grant you that I’m better at it now, and they would probably be closer…. And that some people will be able to keep them in sync pretty much all of the time.

But I think that managing the set point from a blink HUD and using a fixed ppO2 computer is a particularly bad strategy to use when learning to dive a rebreather.
 

PepeUSMC

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Thanks for the input..... I was assuming as much, but I wanted to see if I was overthinking things. The cost is not the concern, when you are buying a rebreather the cost of the computer with it is negligible. I would use my mk2 as the backup certainly, because I like the log profiles and the gps features among other things. I also use my MK2i to monitor my wife and sons tank pressures right now as we all use garmins,... so I would like to keep that ability as well.

But that answers my questions, I will get a rebreather computer and it will be my primary underwater source of information for my breathing.... the garmin can still log my depth profiles and gps set points and keep an eye on my boys tank.

I appreciate the help!!
 

tbone1004

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@grantctobin I don't know if they're still making hardwired computers or not, but if they are, they are a terrible idea if you are diving salt and I strongly urge you go to a 4-pin connector. Corrosion likes to make its way up the cable even though they are waterblocked and it's WAY expensive to send the entire head off to have the cable replaced compared to replacing the 4-pin stub
 

nadwidny

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I have a KISS classic. I run it now with a Nerd 2 on a Fischer and Petrel2 on a 4 pin. This is new.

I used to run it with a Nerd on a Fischer and a hardwired Predator but on a remote trip the Predator flooded so I ran with the Nerd and used a Teric for backup. I managed to keep the deco times very close but it took a lot of attention to keep the PO2 in the loop the same as what the Teric was set for. It worked ok for a backup but only because I had 10 years of experience with the unit. If I was new, I wouldn't do that.
 
https://www.shearwater.com/products/perdix-ai/

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