Challenge Question

[Mike]

Hey Tony,

Skip ,Marbry & I have done the black water thing in the Cooper River.
Found all kinds of sharks teeth & prehistoric bones ( but we obeyed the law & didn't bring em' back .
We dove with Capt. ( you know what your do'in now get your ass off my boat ) Tom McMillan, great guy, put us right on the stuff.
We'd love to get back over there some time & hook up with you & do it again.

Mike M

[skip]

After that, I made a line cookie with my initials on one side and "I have left" written on the other. Never used it, but it would be a nice way to prevent your buddy from endangering himself looking for you when you had already gone.

Now that's a really good idea.

I can't think of one reason I'd want manifolded doubles instead of a sidemount rig.

I'd suggest the so-marked line arrow be one of the larger yellow ones, to make it distinct so you don't accidently use it.

And I really don't understand the advantage of sidemount rigs. I have been going back and forth between sidemounting lp95's and backmounted manifolded 130's. It seems to me that if you have a blown first stage you have to shut down that tank and it won't deliver gas to the second stage even if you crack it open from time to time (the gas just escapes from the blown first stage). So wouldn't a manifold allow you to access the gas in the tank with the blown first stage? Isn't that the whole point of the manifold and why independent doubles (backmounted, banded) is not so common anymore? Manifold introduces two new failure points, but I think empirically the cross bar has not failed often enough to warrent rejecting the rig.

I don't mean to usurp this thread, and know that this sidemount/backmount discussion has taken place before (more than twice), but I must be thick. I just don't get how sidemount is superior to backmount in terms of gas management/emergencies.

-skip

[Tony]

Mike.. Capt Tom provides a nice service. I have never dove with him, but I have heard only good things.

Black water river diving is what we do here... so please feel free to come down and join us anytime!! Our boat can handle 3 divers easily... can put 4 or 5 in with tight quarters.

I'll let you know when the water gets warm enough

[Cindy]

Hey Skip, For one thing the valves and hoses are in front of you where you can see them, not behind your head! I have redundant hoses that are long enough to fit either my inflator or wing. If I shut down one tank I am no worse off than when the first stage exploded. I broke the valve off a tank when I was sidemounting one time and all I got was a nasty bump on my boob, as apposed to the knot on my head that I got when the backmounted first stage exploded. I'm lucky it didn't knock me out or I would not be typing now. Boobs I can replace! LOL
I can't pull a tank off a manifolded rig and keep one on to go through a restriction...I can think of many more reasons to go sidemount. Cindy

[skip]

Cindy, so you are saying sidemount has other advantages that make up for or outweigh the one advantage of a manifold (which is access to the gas in the tank with exploded first stage)?

And even then I suppose you could remove the busted first stage and breath the remaining gas directly off the tank valve, if you must, since with sidemount the tank is there in front of you (well, easily brought around to the front).

-skip

[DeWayne]

With sm it would be a lot easier to take a working reg off an empty cylinder and replace that blown reg should you need the gas that cylinder still holds. You also would not have to worry about possibly loosing additional gas from the good cylinder while attempting to isolate and/or shut down the bad one. That is why instructors typically teach to isolate first, to save as much gas in the good cylinder as possible when you are not 100% sure of the cause for the leak.

[aainslie]

I like to think in terms of probabilities. With a set of manifolded doubles, IF you're quick, you have a reasonable probability of saving the majority of your gas. But IF you aren't (perhaps because the failure was explosive, as happened with Cindy) then there's some probability of losing most or all of your gas. In other words there is a continuum of possible outcomes, from saving way more than halftosaving way less than half.

There's a story in Exley's "Caverns Measureless..." where he talks about his partner having an O-ring fail on one side, and swimming all the way over to Sheck because he didn't think it was his system that had failed. By the time he got to Sheck and realized it was his system that was leaking he had almost run out. They shared Exley's, and only just reached their stages before running out of air.

By contrast, the WORST that can happen in sidemount is that you lose one tank. if you always reserve enough in the other tank then with probability 1 you have enough gas to exit on. This gives more predictability to the system.

Basically with backmount you could end up with more usable gas than is necessary to exit... or you could end up with less. The latter possibility is the one that I find troublesome.

This is above and beyond the huge benefit of having regs where you can see them, ease of removal, etc etc.

[aainslie]

oops -double post. Sorry!

[BillGraham]

I broke the valve off a tank when I was sidemounting one time and all I got was a nasty bump on my breast, as apposed to the knot on my head that I got when the backmounted first stage exploded. I'm lucky it didn't knock me out or I would not be typing now. Boobs I can replace! LOL

Holy CRAP! I didn't even know that was possible.

[Cindy]

It wasn't a modern tank valve. I had borrowed an old 72 from a pal with a needle valve on it. It sticks straight up and you fit the yoke valve over the top of the valve. I wish I had a photo. Anyway I was bulling my way through a sand restriction that I was stuck in and smacked the tank against a limestone outcropping. Scared the poo out of me. My tank emptied very fast. Thankfully I was able to finish digging my way through the sand and made it to my stage. Now you went and blew my next challenge story! Cindy