Doubles: manifolded vs other

[Bismark]

Hi Dave

Okay, so in the interests of furthering my education, please give me your rationale for why you chose to dive independent doubles? Look forward to hearing from anyone else. I laid on extra koolaid for this one Dave!

 

[JeffG]

Hi Dave

Okay, so in the interests of furthering my education, please give me your rationale for why you chose to dive independent doubles? Look forward to hearing from anyone else. I laid on extra koolaid for this one Dave!

I guess that would be when he isn't diving his Meg.

 

[wedivebc]

Hi Dave

Okay, so in the interests of furthering my education, please give me your rationale for why you chose to dive independent doubles? Look forward to hearing from anyone else. I laid on extra koolaid for this one Dave!

I have a few reasons but one is convenience when travelling. I can always set up a set of independants using rental gear. From a safety standpoint I don't buy the failed manifold argument against manifolds and in fact I am not against them. I don't believe IDs are any less safe than MDs since when operated correctly will never render the diver with less than enough gas to complete the dive assuming they consume the same amount on exit. Those that argue higher stress, diving a siphon etc are free to augment their turn pressure, as MD divers also do to add their margin of safety. The task loading iargument is a crock since I can train an open water diver to monitor one SPG and even safely remove and replace a reg. A tech diver surely can monitor 2 SPGs and change regs twice during a dive.
The big advantage I see to IDs is should a major failure occur with MDs a valve shutdown drill is immediately required to safe life giving gas. With IDs the diver can ignore the failure for long enough to locate guideline, pull himself out of a restriction or anything else that might increase chances of survival then shut off those annoying bubbles. This system works equally well either solo or when with another independantly configured diver. I can think of no single failure that will render a ID diver OOA.
And yes Jeff I try to avoid OC diving these days unless absolutely neccesary (like bailout)

 

[Bismark]

Okay, what about the view that the failure is most likely to occur on the right post (the working post) and shutting that post down actually saves the entire remainder of my gas supply vs a post failure which means you are automatically restricted to 50% of your supply? As far as losing gas from a failure, it takes me about 5 seconds max to shut down my isolator. (I do understand about the problem of being in a restriction, etc and not being able to reach my manifold) Then I am in the same boat you describe. I guess the trade off here is balancing the statistical chances of what is likely to fail. Have I missed anything here?

As for the extra SPG, one more thing to go wrong, but again, just a question of statistics.

Is this an accurate summary of the MD versus SD argument? It can't be that simple can it? What did I miss?

 

[wedivebc]

Okay, what about the view that the failure is most likely to occur on the right post (the working post) and shutting that post down actually saves the entire remainder of my gas supply vs a post failure which means you are automatically restricted to 50% of your supply?

I am not sure where that statistic came from. I have seen several LP hoses fail and they didn't care which post they were connected to. A hose could easily get damaged while passing though a restriction on a wreck. Not a good time to be performing valve shutdowns.
Again I don't see a need to save more than 50% of the gas. And that is only at the far reaches of the dive. A failure any time before the turn point will result in more that 50% even for the ID diver.
If I am in a cave or wreck and the bubbles fly and vis goes to zero I want to have my hand on the guideline not on the valves. I will not be stressed knowing I have enough gas to make the exit.

 

[wedivebc]

As for the extra SPG, one more thing to go wrong, but again, just a question of statistics.

Take your favorite reg, connect to a full al80 and record tank pressure. Remove SPG and open tank for 30seconds. Re-attach and record pressure. Now remove hose from LP side and perform same test and let us know what pressure changes occured.

 

[Bismark]

I am not sure where that statistic came from. I have seen several LP hoses fail and they didn't care which post they were connected to. A hose could easily get damaged while passing though a restriction on a wreck. Not a good time to be performing valve shutdowns.
Again I don't see a need to save more than 50% of the gas. And that is only at the far reaches of the dive. A failure any time before the turn point will result in more that 50% even for the ID diver.
If I am in a cave or wreck and the bubbles fly and vis goes to zero I want to have my hand on the guideline not on the valves. I will not be stressed knowing I have enough gas to make the exit.

Would be correct here then to say this scenario is applicable to a LP hose failure only and not a failure with the 1st or 2nd stages where the moving parts actually are? I don't have an actual statistic for you here but I think the thinking here may be that the working bits of the right post are working, thus more likely to fail than the bits that are not doing anything.

 

[J.A.S.]

just a question. when you have IDs do you have a full set on each tank. 2 second stages with spg?

assuming you manage air consumption heavily to balance the weight of tanks properly?

thanks

 

[TSandM]

My friends who dive sidemount (a form of independent doubles) have a long hose on one tank and a short one on the other -- one second stage per tank. They do shift their breathing from one tank to the other during a dive, to maintain balance.

My guess is that nobody has any statistics that would prove beyond a shadow of a doubt that one approach is better than the other. Catastrophic equipment failures just aren't common enough to collect big series of them.

 

[Bismark]

My guess is that nobody has any statistics that would prove beyond a shadow of a doubt that one approach is better than the other. Catastrophic equipment failures just aren't common enough to collect big series of them.

Happy for that but I am starting to see cracks in my world view.........might have to call in some heavier hitters......