I want to murder my computer and feed it to the fishies!

[melanie.]

My computer is a Mares M1 RGBM

I have accepted the fact that it is super conservative - it probably would be quite happy with me not even getting in the water! That is ok, deco is quite fine by me. So buddy and I are doing deco dives, slowly adding more and getting a feel for it.

So last Thursday we were doing a deep dive. Max depth hit 150 (in a low spot), though mostly stayed around 120. Plan was to start heading up slowly once my comp showed 20 minutes of deco obligation. No problem, we started heading up with me having 21 minutes (I got entertained by a folding chair I found). Super slow, no warnings that we are going too fast (and it computes for 33ft/min I believe).

By the time we reach 30 feet, I have 27 minutes of deco???? What the heck is going on? I think I missed a stop at 40 feet, but this just doesn't make sense to me. Because my manual tells me my computer will tell me the depth of deepest stop (at this point it was telling me 10ft). But around 40 ft I thought I glanced briefly and thought I saw it counting a stop. So I stopped and looked again but it was gone.. go down a few feet and nothing! So if I really had to do a stop why wouldn't it show back up when I went to that depth? What else am I supposed to do, other than stare at the damn thing my whole descent? Keep in mind where I am diving is current like crazy and going up a wall and lots of rocks, so generally we "climb" our way to keep a slow ascent, so I just can't watch my wrist the whole time.

We have a swim for a while at 30 ft looking for the bottom to start coming up more (getting into a bay). Deco slowly counts itself off, by the time I get to a perch to stay at I am down to 20 minutes of deco again. Meanwhile buddy only has 5 minutes left (good old conservative computer of mine!). Anywhos we dig in to hang out.

It takes 25 minutes to clear the 20 minutes of deco!!!! (ie watching bottom time add up faster than it is taking deco off). I am at exactly 10 feet and not moving! And the waves could not have been more than 6 inches. Why is this thing not taking time off as it says it will?? At this point I said screw the added safety stop it wanted because realistically I did it already, and more. Before when this happened to me, I always thought it was just because I wasn't maintaining the depth good enough (just floating deco). But here I was set and wasn't moving. So I just don't understand.

Does anyone have some experience with this computer? Because I have no problem listening to it, but I really would like it to hold up to it's end of the bargain. It's getting hard to plan a dive when I have no idea how cranky this computer is going to be with me. I have read the manual front to back and could really use some insight as to how to please this thing.

 

[blatter]

Hi - One obvious explanation of increase in deco obligation from 21 to 27 minutes during your ascent is that may have been a little slower than the computer was calculating for. If the computer is "expecting" you to ascend at 33 ft/min but you ascend at a slower rate, then you will be on gassing at a faster rate than initially predicted by the computer. This would be particularly noticeable at depths greater than 30 ft on a dive profile such as you have described, and it will add additional time to your stops (IMHO this is not necessarily a bad thing for a dive like this and I like deep stops and padding shallow stops as well but that is another topic. In my opinion, it is definitely better to ascend a bit slow than too fast). Differences between you and your buddies computer may also be partially explained by relatively small differences in depth / time exposures / ascent rates in addition to different computer model. A conservative dive computer is not necessarily a bad thing.

I am not familiar enough with Mares computer to take a guess at what was happening on your 10 ft stop or the deep stop, but seem to remember that it needs to be set up to do deep stops and that this would be clearly displayed if required. Currently, I use a couple of shearwater computers and and a suunto computer myself and think that for more technical diving a more technical computer (such as shearwater predator or liquivision xeo or OSTC) can provide more information and may be more cost effective than more mainstream computers (such as suunto or mares) in many circumstances. To illustrate this, one of the good things about the Shearwater Predator is that it can display gas tension to give a view of off gassing effectiveness and also has an @5 function which predicts deco time obligation if you remain at the same depth for another 5 minutes. My suunto vytec ds is not as useful but does tell you if you are off gassing or on gassing when you have obligatory stops. Both computers provide additional information that can inform the diver about their deco obligation. Of course this sort of information is based on a particular computer model which may or may not relate to diver physiology. If it is working correctly and used correctly, I am sure your mares computer is is fine BTW.

Deep stops, good hydration, controlled ascents, padding stops and decent surface intervals are all very good ideas in my view (and based on a few thousand dives worth of experience, including many many deco dives). During deco dives I would also take at least 2 computers in case one fails as I like to be able to ascend independently - and being without a backup (computer or tables and bottom timer) with 20 minutes + of deco is not a trivial situation if your computer breaks.

Deco for Divers by Mark Powell is useful reference for deco diving that you may find interesting, and v-planner software and other deco programs are an interesting way to illustrate different dive profiles and deco obligations.

 

[melanie.]

Thanks blatter - great info! I will work on my ascents more. I have been overly cautious because my computer will scream to high heaven if I go up to fast. Next time I will try going a little faster to see if that is what is adding the extra deco. Not that I mind going up slow I just want to understand my computer.

As far as the deep stops, the manual says that it calculates it automatically based on each dive. So it is set to go, but I don't know how to tell ahead of time what it will want from me. I should see if I can simulate a dive on it to see if it will tell me ahead of time. I have only used the plan function for repetitive dives, to see how much bottom time I have with the current surface interval

 

[ianr33]

Do you have any deco training or are you just figuring this stuff out as you go along? What tables were you using for backup in the event of a computer failure?

 

[Jim Lapenta]

Ditto to what ianr33 said! That you planned a dive with 20 minutes of deco obligation yet went over that by 1 minute. That tells me you do not have the discipline to be doing these types of dives.

What was your planned bottom time? Not your deco time but how long did you plan on staying on the bottom to incur this deco?

At what depth? What was your planned air usage?

What contingency plans did you have and what back up if the computer crapped out?

THat you don't know why your computer added deco is also troubling. You don't know it well enough to be using it for this. It sounds like you are putting all your trust in it and that is very foolish.

You also admitted that you are asking the computer to monitor your ascent rate. Why are you not aware of how fast your are ascending without it?

Doing deco dives and not knowing this stuff gets divers hurt and puts others at risk if they have to assist you.

I'd advise you to stop this and get some training. Put the computer into gauge mode and PROPERLY PLAN YOUR DIVES. What you're doing now is playing russian roulette and not even bothering to count how many rounds are in the gun.

 

[drbill]

I have to agree with the previous two posts. You have 100-200 dives yet are doing deep (150 ft) dives with significant deco obligations and using a single computer (although you have some redundancy with your buddy's computer). Are you diving single tanks? Al 80s? What would happen to both of you if a reg or tank valve failed? Do you at least have pony bottles with you? Just think you are way over your level of training and experience.

I've done LOTS of dives in the 150-200 ft depth range but always have redundancy in terms of air supply and computers. I had one computer fail on me years ago during a 27 min deco obligation. Never again will I do a deep dive without a backup (second computer since my deep dives are not necessarily pre-planned because my goal is filming critters rather than doing a more predictable dive profile such as on a wreck).

 

[melanie.]

While I appreciate your input (Ian, Jim, drbill), I hope you understand that this thread is to discuss my computer - not my diving habits. Now I could go through though the posts and defend myself about the assumptions you are making (not planning, ascent rate, tank sizes, redundancy, discipline etc etc), but again that is not the point. I have a great instructor, a solid buddy, and I am going to learn whether you feel I am prepared to be making these dives or not.

So if anyone has any experience with the Mares M1 RGBM computer that is helpful - I would love your input. Specifically - is there a way of knowing when deep stops are coming up, why it doesn't count down deco reliably, and any other knowledge you can pass on.

Thanks guys

 

[ianr33]

I'm not familiar with your computer. Some quick googling shows it appears to be a recreational computer (no matter what the sales literature might say) IMHO you are using the wrong tool for the job.

If you are going to use a computer as the primary mean of deco planning get one that's designed for that. (Shearwater Predator or LiquivisionX1) Neither of these are cheap but you gotta pay to play.

EDIT: From page 4 of the Mares M1 Manual:

<<Recreational divers should NOT dive deeper
than 40m (130 ft). Although this computer
will continue to provide information for
compressed-air dives deeper than 40m
(130 ft.), the risk of nitrogen narcosis and
decompression sickness (DCS) is greatly
increased; therefore this information
should be treated as only approximate. >>

Suspect you may be using it outside of it's design parameters and it's response is to give you a bunch of deco due to the advice of Mares lawyers.

I have an Aeris computer that does something similar. If I do a 60 foot or therabouts dive followed by a 130 foot deco dive the computer starts asking for an insane amount of deco. (Maybe 50 minutes compared to 10 minutes on my Predator)

What are you going to do when your computer wants an hours deco and you only have 30 minutes of gas?

 

[inventor]

My tech friends have LiquivisionX1's. They are officially the $%#@.

 

[=C=]

Edit- removing info on a diff model-

My dive buddy has the M1 and versus my Galileo it seems to be slightly less conservative. I hit NDL first so your post strikes me as odd.

Here's a relevant thread: http://www.scubaboard.com/forums/archive/index.php/t-44529.html

From your description and reading the google results it sounds like you missed a deep stop and the computer took away a decompression credit it had given to you...

Read a couple of the M1 threads on the board.

This is in the first google result for M1 review: http://www.diveoz.com.au/gear_reviews/mares_m1_table1.htm

And it seems to show a mixed bag if I am reading it right, generally shorter NDL but also shorter Deco in at lease one instance.

Interesting thread! (and like everyone else says: deco shouldn't be undertaken without proper training. Don't know what your story is... but for untrained divers who find this thread: deco by way of trial and error is dangerous and can get you dead)