"Complete Wreck Diving" (manifold vs independent)

[Bill Fisher]

Do more divers using doubles prefer the isolation manifold over
independent doubles ?

I'm still uncertain for myself, but one quote keeps coming back to me, it's from the book "Complete Wreck Diving" by Henry Keatts & Brian Skerry.

After reading the passage from the book, please tell me why you prefer an isolation manifold over independent doubles....or vice versa.

I know this has been covered a ton, so please either reply or ignore.

Thanks. Bill

"With the basic double manifold design,a single regulator is used eliminating the need to switch regulators during the dive. The obvious downside to this is the lack
of redundancy. Should the manifold or regulator malfunction, there are no options. An example of just how dangerous this lack of redundancy can be is illustrated in a story told by Larry Keene of Ocean City, MD.

"While diving the wreck of the U-853 off Block Island several years ago, I had a first hand lesson in the importance of a back-up system. I was exploring inside the foward torpedo room when in the confined space, I rubbed against some sharp jagged metal which sliced my regulator hose in two. Alll the air in my double tanks completely drained out in seconds. I forced myself not to panic, exited the loading hatch and saw my buddy approximately 30 feet away. I had two choices, swim to him or the surface. I made the decision to swim to him and buddy breath. I made it to him, and we were able to buddy breath to the surface. I'm lucky I did not have to decompress. From that moment on I never went diving without a redundant system"

The author doesn't go on to say what type of redundancy,
independent doubles or a pony in addition to the manifold doubles he uses ???

 

[PerroneFord]

"While diving the wreck of the U-853 off Block Island several years ago, I had a first hand lesson in the importance of a back-up system. I was exploring inside the foward torpedo room when in the confined space, I rubbed against some sharp jagged metal which sliced my regulator hose in two. Alll the air in my double tanks completely drained out in seconds.

U-853 is in 130ft of water according to reports. I had a LP hose go at ~70ft (left post). By the time I shut that side down I'd lost ~200psi.

I'd be interested in hearing other experiences but I'm not quite ready to toss the manifold out yet. Sidemount and CCR excepted.

 

[MSilvia]

If you have an isolation manifold, you should be able to prevent a catastrophic loss of gas by isolating the doubles from one another and shutting down the problematic side.

It seems to me like the situation describes manifolded doubles without an isolator valve using a single regulator. Doubles using an isolation manifold and a seperate regulator on each post are quite different.

 

[Soggy]

An isolation manifold allows you to access *all* of the gas in both tanks in the event of a regulator failure, which is really the most common type. The isolator is there in order to isolate the tanks in the event that the tank oring or burst disk blow. Only a failure of the isolation valve itself (which I've never actually heard of occurring underwater) would cause a catastrophic loss of gas. That's why you bring a buddy. An isolator manifold greatly simplifies a number of procedures underwater including gas donation to a buddy. If you dive with a buddy routinely, I feel it is far superior. I would not dive with someone on independents.

That being said, if you are always solo and need absolute redundancy and have no hope of a buddy being there to provide you with gas if your numbers hit in the bad luck lottery, I think independents might be the way to go.

You have to ask yourself what is more important...having access to all your gas in the event of a common failure or saving half your gas in the event of an highly uncommon failure.

Perrone, you are correct. The U-853 is ~130fsw.

 

[Bill Fisher]

Thanks for the replys...

MSilvia I think you hit the nail on the head...

It seems to me like the situation describes manifolded doubles without an isolator valve using a single regulator. Doubles using an isolation manifold and a seperate regulator on each post are quite different.

Having only one regulator may have been what he meant by never diving without redundancy again ???

Bill

 

[Gilldiver]

"While diving the wreck of the U-853 off Block Island several years ago, I had a first hand lesson in the importance of a back-up system. I was exploring inside the foward torpedo room when in the confined space, I rubbed against some sharp jagged metal which sliced my regulator hose in two. Alll the air in my double tanks completely drained out in seconds.

That book was writen back about the mid 90's and the event happend back in the 80's or so. If I remember right Larry was using a cheater bar which hooked two tanks together but you only had one regulator post. So, in this case Larry lost it all when the hose went. There was no way to shut off and go on a backup. This is one of the reason many used pony bottles as their backup.

With a real manifold with two posts & regs, even without an isolation valve, he could have shut off one reg and got out fine. Which is what Brian and Hank were getting at.

 

[Thalassamania]

The incident mentioned could have been solved with any redundant system be it isolation, Benjamin or independent.

I prefer independent since you can rent two tanks anywhere and the only price you pay for that system is a bit of task load changing regs, which I'm comfortable with. An isolation manifold is great if you want to avoid that problem and the only price there is an additional failure point that I've never seen fail. Benjamin rigs (thought I have some) seem to me the worst of both worlds but that "worst" is at a very low level, you gain by eliminating the isolation failure point and lose by not being able to save your gas if a neck o-ring or blow-out plug were to go during a dive (also something that I've never seen).

 

[JEScholz]

Is this what you call a "Benjamin rig"? I have never heard that term before.

 

[daniel f aleman]

I use independent doubles for wreck, and a pony, (and a stage if needed) - all common sense says why...

 

[Thalassamania]

No, a Benjamin Rig is a doubles manifold with two outlets, each with its own control knob but no isolator.