pony or spare air?

[Tortuga68]

I mount my primary first stage on my right hand post with my primary second stage regulator on that first stage side. My octopus is mounted on the other left hand side of my isolation valve on every set of doubles I own (I don't dive single tanks). Then I sling a 30 cu. ft. pony bottle as another redundant system. Oh yeah, I just happen to carry an AIR2 also

Can we see a photo of this setup please?

 

[doctormike]

No. I said the same thing without the math you used - At some point you have to say 'this (failure) is possible, but highly unlikely'

Yup, you may be right...

 

[NC Wreck Diver]

Uh... actually you have done a very good job of increasing your chance of equipment failure. What you did decrease is the chance of not having available air due to failure. Nit picky, I know.

In the end, our environment has a huge impact on failure and gear choices. Example: The odds of loosing you air to a 1st stage free flow are substantially different by orders of magnitude when comparing 40F- to 55F+ water.

Well, we all have our right to our opinions. If this is your's, that's cool. But in 1500+ dives, and the very well maintained, high quality regulators that I use, I have never had a failure of my systems. Nit picky, maybe, but as I mentioned, your opinion is your choice, and it is good to be shared. I'll still dive my rig the way I posted. Thanks.

 

[Tortuga68]

What you did decrease is the chance of not having available air due to failure

Can you explain this?

 

[doctormike]

Can you explain this?

I can..! I can..! Pick me..!

(Sorry, no offense...)

When you multiply numbers less than one, you get a smaller number. When you add them, you get a bigger number.

So if the probability of failure for each of your three RAS is 0.01 (1%), then the probability of ONE of the three of them failing (i.e. the probability of AN equipment failure) is 3% (0.01+0.01+0.01=0.03). So by having three systems, you have increased the chance of any one of them failing.

But we are not really concerned with equipment failure rates (we can't affect that, that's up to the manufacturer). We are concerned with the consequences of equipment failure (not having air). And in order for THAT to happen, all three systems need to fail simultaneously. In THIS case the probabilities are multiplied (0.01x0.01x0.01=0.000001) giving you a one in a million chance of not having air, in this particular scenario...

Wow, I miss 7th grade...

 

[GrumpyOldGuy]

Can you explain this?

edit: DrMike beat me to it....

Sure, you have 3 1st stages. Each first stage has a failure rate of lets say 1:100000 (example). The chances of you having a failure in any one of the 3 1st stages is the sum or 1:100000+1:100000+1:100000 or 1:33333.

Of course the chances of having a failure in all 3 (and being OOA) is now the product (not the sum) and 1:1000000000000000 (plus or minus a zero if I have a typo)

It is a nit picky point, but does illustrate that as you add complexity to your system, the odds of something going wrong increases. Thus the increased need for practice and training with the more complex systems and one more reason why a SA/RAS may not be the right move for a novice. To an experienced diver, the added complexity is probably moot.

 

[Tortuga68]

Do either of you know what an isolation manifold is? Put your slide rules down for a minute

 

[doctormike]

edit: DrMike beat me to it....

Damn. I'm still such a geek. No wonder I didn't go to my high school prom...

Sorry, Grumpy..!

 

[doctormike]

Put your slide rules down for a minute

Never! I consider that critical life support equipment.

I have the Halcyon DeepMath 1000 slide rule, standard gear on all Andrea Doria dives, from what I hear. Also, I keep a backup in my sock. I just haven't figured out how to deploy it without taking my dry suit off underwater....

 

[Tortuga68]

Yeah, high fives all round. Never mind that neither of you addressed the question that I was actually asking...