Independent Twins

[wedivebc]

then you deserve to drown? hehehe

anyway, here's my question:

how would independents help you anyway? your left tank is gone, and your
right tank has *some* gas. how is knowing exactly how much (by using your
gauge) going to help the situation any?

independants help because no matter where you are in the dive you can't lose more gas that it took you to get to the turn point so even in the worst case, the turn point, no failure can claim more gas than you need to get out. Not so with a manifold. My point with the spg is, you know you're toast just not when.

 

[H2Andy]

i see now

in your scenario, with total loss of integrity of one cylinder, you would be loosing
air from both until you managed to isolate them...


hmmm.... extreme scenario, though, and it assumes no buddy

 

[DA Aquamaster]

What brand of travel band have you used? Mine is Aqua Explorer band with the plastic buckles that might not be a good for the cold water diving. It works fine with AL 80s.

I use aqua explorer bands year round. I have some problems in the winter with the plastic cam buckles breaking due to near zero air temps, mostly after the dive if I leave things connected long enough for the bands to begin to dry as they will contract enough to crack very cold plastic buckles.

In the summer bottom temps are still near 40 but I have have only broken one in about the last 200 dives.

So, how much air do you leave on both tank at the end of diving? I used to remain 500 psi each AL 80 tank.

I plan for a 1/3rd reserve. Consequently with steel tanks filled to 2400 psi I will switch at 1600 psi for the right tank and 800 psi for the left tank and plan on ending the dive with 800 psi in each tank. With AL 80's it's the same story but with switches at 2000 and 1000 psi and 1000psi left in each at the end of the dive.

As was already stated, they screwed up long before you came upon them with poor gas management.

I agree completely.

If it is an unintentional deco situation, the diver has already screwed up, but unless he has screwed up really badly, 1/3 of one tank should still be more than enough to get the diver out of the deco situation which leaves 1/3 in the other tank for the OOA buddy.

It's also getting increasingly unusual for divers to do deco on back gas anyway given the much greater efficiency of deco gases like 50%, 80% and 100% O2. That means that in intentional deco situations the properly configured technical diver with minimum Adv. Nitrox and Deco Procedures certifications is going to be configured with doubles and at least one deco gas in a slung 30, 40 or 80.

I do a contingency deco plan in the event my deco gas is unavailable and will consequently ensure that the 1/3 reserve back gas is adequate to cover the longer deco obligation required on my backgas.

What this then also means is that in the event my buddy ends up completely OOA with a remaining deco obligation, I would still have the ability to hand him or her my deco gas and then complete my deco on my backgas. It's also a pretty safe bet that if the buddy ended up completlely OOA (ie: lost both all the back gas and deco gas) that I would never dive with him or her again.

Using a deco gas also eases the gas planning somewhat as you can then plan to have 1/3 remaining at the 70 ft stop (if using 50%) as long as the 1/3 reserve is also adequate to complete the longer deco obligation on your backgas. Even with relatively small doubles like steel 72's or Al 80's I can plan for 20 minutes and 25 minutes respectively at 150 ft and still have an adequate reserve.

Even if you lose all the gas in one tank at the turn point (worst case scenario) and have only the 1/3 remaining in the other tank, it will still get you to the first deco stop and from that point you will be making a normal ascent on your deco gas anyway.

 

[wedivebc]

Even if you lose all the gas in one tank at the turn point (worst case scenario) and have only the 1/3 remaining in the other tank,

I think you mean 1/3 total gas here right, not 1/3 of that tank? Because at the turn point both tanks should have 2/3.

 

[lairdb]

You don’t need to sacrifice two tanks only for the double set up. Wherever you go with double travel band, you can set up the double within 5 min. I am not sure how many charters allow you to set up the double with your own manifold.

Sooo, all this has prompted a thought -- what would the fatal flaw be of a "soft" manifold? I.e., an HP hose connection directly between the two "independent" regs? Perhaps even with an isolator in-line?

 

[Hoosier]

DA Aquamaster,

Thanks for your further explanation. I don't get into the tech area yet so I don't even think about the deco utilization. I learned one thing from you again tonight.

I know you are using the same band as mine. As I said in the initial post, you were the person who recommended this setup to me. You might forget it though.....


http://www.scubaboard.com/showthread.php?t=99416

Sooo, all this has prompted a thought -- what would the fatal flaw be of a "soft" manifold? I.e., an HP hose connection directly between the two "independent" regs? Perhaps even with an isolator in-line?

I think you are talking about "Universal manifold" that has been posted in other thread.
http://www.scubaboard.com/showthread.php?t=99416 Check it out.

 

[2TH DIVR]

I know it's not a necessity to be able to shut down a tank with independant doubles'
but how many use tanks with right and left valves?
How easy would it be to get at the valve handle centered if you were using 2 rights?
I favor a manifold.
If it comes down to the few dives where I needed the extra air (vacation) I will just sling it.

 

[cool_hardware52]

Sooo, all this has prompted a thought -- what would the fatal flaw be of a "soft" manifold? I.e., an HP hose connection directly between the two "independent" regs? Perhaps even with an isolator in-line?

A true manifold connect the tanks before the valve. Connecting the HP ports of two first stages offers no advantage. If you need to shut down one post (reg ff or hose failure or whatever you have lost access to the gas in that tank.

Adds failure points, solves nothing.



Tobin

 

[WarmWaterDiver]

I know it's not a necessity to be able to shut down a tank with independant doubles'
but how many use tanks with right and left valves?
How easy would it be to get at the valve handle centered if you were using 2 rights?
I favor a manifold.
If it comes down to the few dives where I needed the extra air (vacation) I will just sling it.

It depends on the individual IMO - you might as well ask "How hard is it to drive a vehicle with manual transmission versus an automatic transmission?", to go back to wedivebc's analogy. If one is sidemounting, it would appear to be MUCH easier, than with pre-manifolded back mounted doubles with center isolator, as one example.

I have never yet used independant doubles with a 'right' and 'left' hand tank valve - in fact, I don't think I've ever seen any 'left' tank valves mounted on rental tanks anywhere we've traveled, unless they were already connected to a manifold with center isolator.

But, if one had an extreme concern with this, why not mount the left tank 'backwards' from the right tank? Is it some special 'rule' that both first stages must reside between the tank valve and the diver?

Personally, even with manifolded doubles and center isolator, I still use one SPG per first stage, but I'm a data freak, observing and analyzing data is how I earn my bread and butter, and the risk management issue to me is acceptable - just what I do, not a recommendation nor endorsement for anyone else. There is 'nil' additional task loading for me to do so personally, and I don't solo dive. I would be much more stressed by 'flying blind' at any point in the dive on remaining gas pressure.

Different strokes for different folks.

 

[drbill]

... But, if one had an extreme concern with this, why not mount the left tank 'backwards' from the right tank? Is it some special 'rule' that both first stages must reside between the tank valve and the diver?

The regs are more protected from bumping, etc., if both first stages are between the tank valve and the diver.