Solo and Redundant Computer(or how is most solo diving done?)

[drbill]

I solo dive almost all the time and have worn redundant computers for about 10 years now. I made that decision when my single computer's battery failed (despite saying there was 38% battery power left) during about a 20 min deco stop. Since then, I have had batteries die on me and a computer fail to turn on upon descent so I'm glad I had both of them on.

 

[GrumpyOldGuy]

The stupid battery indicators rely in voltage, they are not linear and are misleading. I find they report 100% for a long time, then drop fast. 50% is replace me now, more like the low gas idiot light on a car. I am a bit paranoid though.....

 

[lowviz]

The stupid battery indicators rely in voltage, they are not linear and are misleading. ...//... I am a bit paranoid though.....

I really hope I word this correctly.

OK, it sounds like you are setting yourself up for a serious "OH S$$T" moment if you are ever drawn into any real amount of deco. So let's break the problem down.

1) You only have so much gas. This limits what you can actually do underwater as opposed to what you could do "in theory". If you are somehow kept overlong on the bottom and then released with a given amount of gas, how would you spend it on the way to the surface?

What I'm trying to get across is that always knowing what is "best" at any given point in the dive (as opposed to relying on your computer(s)) helps prevent mental meltdown when issues start to pile up in solo diving.

 

[GrumpyOldGuy]

I really hope I word this correctly.

OK, it sounds like you are setting yourself up for a serious "OH S$$T" moment if you are ever drawn into any real amount of deco. So let's break the problem down.

1) You only have so much gas. This limits what you can actually do underwater as opposed to what you could do "in theory". If you are somehow kept overlong on the bottom and then released with a given amount of gas, how would you spend it on the way to the surface?

What I'm trying to get across is that always knowing what is "best" at any given point in the dive (as opposed to relying on your computer(s)) helps prevent mental meltdown when issues start to pile up in solo diving.

I know its Saturday and maybe you have had a couple of beers and jumped the gun. Of course I have had a few, so connect the dots for me if I am not coherent.....

There is no connection between my distrust of battery indicators and planning for deco. They are totally independent. I don't trust battery indicators be be much more than good or getting low. Being careful about letting a computer battery getting low does not lead one into serious deco obligations. I do agree, at any time in a dive you should know how to conduct a safe ascent w/o a computer. That does not mean you should not take care of you gear and maintain it in the best possible condition.

 

[lowviz]

I know its Saturday and maybe you have had a couple of beers and jumped the gun. ...//...

OK, I obviously didn't word it correctly.

50% of what? http://www.mpoweruk.com/performance.htm Can you point to your 50% point?

 

[GrumpyOldGuy]

OK, I obviously didn't word it correctly.

50% of what? Battery Performance Characteristics - How to specify and test a battery Can you point to your 50% point?

Yup, that happens sometimes on SB. I was referencing 50% of the battery bar graph typical on dive computers. The bar graph is driven in s/w by a voltage sensor, which is related to the remaining, usable power in the battery. The voltage decay curve typical of good batteries drops very slowly until the battery is nearly depleted, then drops quickly. This leads to battery indicators that do the same.

I bet you a beer if you time how long your smart phone takes to go from full charge to 1/2 charge on the indicator, that it is a lot longer than from 1/2 to dead. Same principle.

 

[lowviz]

So we both agree that 50% is no where near the middle.

OK, the point that I was going for was that for anything over 60 cuft, there is a dive that will put you into real deco. The better your SAC and the more gas you have, the bigger the "threat". A person that is overly concerned about doing anything to avoid going into deco can be set up for panic if that person even THINKS that he/she strayed into an obligation. Something as simple as noticing that your computer was set to nitrox while you are diving air can start the "cold sweats". One should be able to both question and do without one's computer. I see PDC's as great conveniences, not necessities. YMMV.

 

[drbill]

The stupid battery indicators rely in voltage, they are not linear and are misleading. I find they report 100% for a long time, then drop fast. 50% is replace me now, more like the low gas idiot light on a car. I am a bit paranoid though.....

Problem with the one I had that failed at 38% remaining battery life (RBL) was that the manual clearly stated that even once the RBL read 0% you still had enough juice for a few more dives. I discovered after mine failed that most of the computers of that specific model failed at between 25 and 47%. I read the manufacturer the riot act on that potential liability issue. They admitted that the RBL indicator used an algorithm rather than a direct read.

 

[GrumpyOldGuy]

Problem with the one I had that failed at 38% remaining battery life (RBL) was that the manual clearly stated that even once the RBL read 0% you still had enough juice for a few more dives. I discovered after mine failed that most of the computers of that specific model failed at between 25 and 47%. I read the manufacturer the riot act on that potential liability issue. They admitted that the RBL indicator used an algorithm rather than a direct read.

That's even worse than I would have thought. Goes back to the old axiom of test to the limits, I guess sometime I should let one of my computer run to 0% and see how it behaves.

---------- Post added June 3rd, 2013 at 09:17 AM ----------

So we both agree that 50% is no where near the middle.

OK, the point that I was going for was that for anything over 60 cuft, there is a dive that will put you into real deco. The better your SAC and the more gas you have, the bigger the "threat". A person that is overly concerned about doing anything to avoid going into deco can be set up for panic if that person even THINKS that he/she strayed into an obligation. Something as simple as noticing that your computer was set to nitrox while you are diving air can start the "cold sweats". One should be able to both question and do without one's computer. I see PDC's as great conveniences, not necessities. YMMV.

I agree. My problem is usually the opposite, my computer reset to air after 4 hours and I am on the bottom realizing I am hitting deco way too fast even though I am on 32%. Then it dawns on me I forgot to set it to 32%. At that point, I don't bother doing the math, I hit deco (based on air), do my 5-10 minutes of hang time and consider it practice deco with little risk. Note: I do know the math, I just prefer not to trust myself doing in my head, on the bottom.

 

[AfterDark]

So we both agree that 50% is no where near the middle.

OK, the point that I was going for was that for anything over 60 cuft, there is a dive that will put you into real deco. The better your SAC and the more gas you have, the bigger the "threat". A person that is overly concerned about doing anything to avoid going into deco can be set up for panic if that person even THINKS that he/she strayed into an obligation. Something as simple as noticing that your computer was set to nitrox while you are diving air can start the "cold sweats". One should be able to both question and do without one's computer. I see PDC's as great conveniences, not necessities. YMMV.

I question if a person so easily rattled should be diving at all?