computer redundancy

[vinegarbiscuit]

I dive with an Oceanic and a Dive Rite Nitek HE. Before I inherited the Dive Rite from my other half (he upgraded to a Shearwater), I flew a Suunto Vyper with my Oceanic. They agreed fairly well on the first dive of the day, but it was always a scream to observe the differences between the two on subsequent dives.

 

[stargost]

I dive a single cheap non conservative computer (DSAT). I like it this way, because I don’t do repetitive dives for consecutive days. So goal is to maximize the bottom time during this/these 1 day dive(s). The DSAT algo has been tested well enough to make me feel good with it, for this kind of diving anyway.

If you go for liveaboard, it seems you are required to have a computer, and if there is a problem with it during your week of intense diving, then you lose a precious day at least + have to go with table if computer is really dead then.
So when I do liveaboard for a week, I’ll certainly buy a backup.

This backup will be a more conservative one due to the repetitive dives (so uwatec or suunto like) and it will actually be the primary, the DSAT will become the backup.
For just one dive, it does not seem that DSAT and RGBM/Bulhman8/16 have significant differences, so why bother. I have noticed it diving with several buddies, and graphs/studies seems to confirm more or less.
But for repetitive days/dives, the non DSAT computers seems to reduce the bottom time vs DSAT. So more security if one wants it.

So would be how I see the need for 2 DCs and why 2 different algos as well.

 

[ApexLongimanus]

To expand a bit on the discussion;

If one were looking to buy a second computer specifically for redundancy should they buy one using the same algorhythm or not?

My thoughts are that one should use the same algorhythm to get the most redundant value from the computer.

If you are running two different algorhythms, you cannot tell if either computer is calculating NDL/time remaining correctly as they will naturally give different values.

If you run two computers using the same algorhythm they should give roughly the same values and if they do not you know one is malfunctioning (unless it can be explained some other way).

I think this would give maximum value, otherwise, one is really throwing away the computer part of redundancy and could just as well use a cheaper bottom timer/depth gauge.

thanks, daleC.

i think the main differences in algos can be seen in different scenarios in decompression diving (ndl diving might give a minute more or less but not have a significant impact IMHO). now, assuming you run buhlmann and vpm, i strongly believe that you find dive plans where one time buhlmann and another time vpm comes out ahead. if you have two computers running different algorithms, and you always go by the more conservative, wouldn't you add some safety margin?

just a thought.

 

[Jorgy]

So which computer did you dive on the subsequent dives the Oceanic or the Suunto?

If the Oceanic did you bend the Suunto?

M

 

[Jorgy]

In Bonaire we dove the Hilma Hooker as a boat dive.....

Son and I with Suuntos the others on the boat with non-Suuntos......we had been diving most of the week together.....

They toured the bottom of the boat, we stayed higher up......

We rode the computers up the line to avoid deco.......

The non-Suuntos still had between 13-18 minutes of NDL.......

There is a huge difference even in recreational diving.......

M

 

[vinegarbiscuit]

Geezuz, you guys are only diving, not going to the Moon...why two computers, waste of money, go on a vacation instead

I used to believe as you did. But:
1). Having had my (old) single dive computer die on my on no less than three occasions - yes, during a dive - I don't intend to be in that situation again. The first time it happened, I replaced the computer (with the same model), and blow me down if it didn't happen again. Fortunately, I always carry dive tables with me - they're in my log book and travel with me on every vacation. I had no problem cutting tables for subsequent dives (a kindly DM/fellow traveler lent me depth gauges and bottom-timers), but in the name of conservatism, I had to skip a couple of dives during the rest of my vacations. Sod that, and never again!

2). Having started down cave diving path, I like the added security and redundancy of carrying two computers.

3). I'll eventually take an Advanced Nitrox/Decompression Proceedings course, and since my Oceanic's not a full decompression computer and handles O2 mixes of up to 50%, it's not really equipped to continue serving as my primary computer. Using my Dive Rite now is great practice, and moreover, allows me the comfort and familiarity of using my old friend, the Oceanic, too.

4). Having a diver as a partner = double the toys. Especially because he's upgraded to a rebreather. Some of his older computers, like his Dive Rite, pale in comparison to the Shearwater he now flies. All the more for me, I say!

 

[vinegarbiscuit]

So which computer did you dive on the subsequent dives the Oceanic or the Suunto?

If the Oceanic did you bend the Suunto?

M

Nope. I'm very proud of the fact that I've never bent the Suunto, even while diving 5 times a day (Roatan and so on). It was mildly inconvenient. My sac rate's pretty good, and I like to make the most of my bottom time, but doing so with a Suunto requires a few modifications, like staying some feet shallower than the rest of the group (having duly informed my mates of my intention, of course). Even so, I would end the dive with only a few minutes of NDL time remaining (meanwhile, my Oceanic was clearing me to stay at 50 feet for another 10 hours!). Last thing I wanted to do was piss the Suunto off and have it go into gauge mode for the rest of the week. Call it pride, call it what you will!

 

[Jorgy]

Yes.....

Since we are Suunto family we often dive 10-15 feet over the others......

In the end I prefer the more conservative computer......darling daughter is now fourteen diving since ten......

We don't push to any limit......depth, bottom time or air......'

So we back on the boat first with lots of air........

M

 

[ApexLongimanus]

In Bonaire we dove the Hilma Hooker as a boat dive.....

Son and I with Suuntos the others on the boat with non-Suuntos......we had been diving most of the week together.....

They toured the bottom of the boat, we stayed higher up......

We rode the computers up the line to avoid deco.......

The non-Suuntos still had between 13-18 minutes of NDL.......

There is a huge difference even in recreational diving.......

M

thanks, i was probably a little too ignorant of that fact. apologies.

 

[ApexLongimanus]

thanks, daleC.

i think the main differences in algos can be seen in different scenarios in decompression diving . now, assuming you run buhlmann and vpm, i strongly believe that you find dive plans where one time buhlmann and another time vpm comes out ahead. if you have two computers running different algorithms, and you always go by the more conservative, wouldn't you add some safety margin?

just a thought.

to add to this (i have deleted the ndl comment):

theoretically, two liquivision with multideco (one running buhl and the other vpm) could do the trick. however, looking at redundancy you are then exposing yourself to identical hardware which could have issues.

again, just food for thought...