Questions about twinsets.

[Brett Hatch]

Personal preference. The theory that a diver whom is probably also on doubles needs to take air from you, the assumption is that their breathing rate is elevated. Since if their on doubles and need to share air from me, something had gone horribly horribly wrong. So the thought is they are going to highly stressed. So my preference is close the isolator so they can only breath through half of my remaining air. This is assuming the need to make stops or at least a safety stop.

My thought is in an emergency where I have to share air, I plan on ensuring I make the surface while hoping that sharing air will get us both to the surface. Someone potentially hyperventilating may empty a cylinder in no time.

OK, thank you for clarifying, that makes sense to me and is plausible. Not sure I agree with the setup -- it's a tough call for a really tough situation -- but I get it. One would hope that their gas planning leaves sufficient wiggle room to allow for OOG buddy's increased breathing rate. Hope nobody ever has to make the call to turn off their buddy's gas to save enough for themselves. But, as they say, s*** happens.

 

[wetb4igetinthewater]

@Scuba_Nick27

I don't think I can add anything to this conversation. I see you are in Florida. If you are in south Florida, I'd recommend speaking with @custureri or @LandonL of http://getaqui.com/. Two top notch instructors that will help you achieve your goals fast.

 

[greeniguana]

My thought is in an emergency where I have to share air, I plan on ensuring I make the surface while hoping that sharing air will get us both to the surface. Someone potentially hyperventilating may empty a cylinder in no time.

Just cut their hose with a giant knife like SeaHunt.

 

[wetb4igetinthewater]

Personal preference. The theory that a diver whom is probably also on doubles needs to take air from you, the assumption is that their breathing rate is elevated. Since if their on doubles and need to share air from me, something had gone horribly horribly wrong. So the thought is they are going to highly stressed. So my preference is close the isolator so they can only breath through half of my remaining air. This is assuming the need to make stops or at least a safety stop.

My thought is in an emergency where I have to share air, I plan on ensuring I make the surface while hoping that sharing air will get us both to the surface. Someone potentially hyperventilating may empty a cylinder in no time.

Are you familiar with the concept of minimum gas?

What do you think will happen when the receiver consumes half of that remaining gas before reaching the surface?

The calculations for min gas have to guess about the stress factor. It comes down to risk management. But if you have gas and the receiver doesn't, I don't think that is going to end well.

 

[RX8Bob]

Are you familiar with the concept of minimum gas?

What do you think will happen when the receiver consumes half of that remaining gas before reaching the surface?

The calculations for min gas have to guess about the stress factor. It comes down to risk management. But if you have gas and the receiver doesn't, I don't think that is going to end well.

I am, but **** happens, and in reality, very very few people know how they would react in a true ooa emergency. Simulate it all you want and figure out your RMV for high workload and such to figure out requisite air, but at the end of the day my intent is to go home. I'm not cutting off their air, I'm just protecting my half. If you've had a catastrophic failure where shutting down a post valve and or an isolator doesn't get you back to the surface (2 strikes), I'll give you half of mine and if you exhaust that, well then I'm sorry, you've had your 3 strikes.

Isn't it in the rescue class where they stress that ensuring your own safety should be of highest priority?

May be an old school way of thinking, but honestly for the situation to get to that point many things would've had to go wrong and my choosing to preserve air for me is the least of them.

So either they really failed to maintain their equipment, or they're diving well beyond their ability and skill.

Additionally, if the recipient costumes both their half and my half then it is guaranteed to not end well for both parties. If they consume the isolated and I still have gas at least I have a chance.

Just cut their hose with a giant knife like SeaHunt.

Yeah I'm no Mike Nelson.

 

[wetb4igetinthewater]

I am, but **** happens, and in reality, very very few people know how they would react in a true ooa emergency. Simulate it all you want and figure out your RMV for high workload and such to figure out requisite air, but at the end of the day my intent is to go home. I'm not cutting off their air, I'm just protecting my half. If you've had a catastrophic failure where shutting down a post valve and or an isolator doesn't get you back to the surface (2 strikes), I'll give you half of mine and if you exhaust that, well then I'm sorry, you've had your 3 strikes.

I'd argue that buddy selection is important. How is this person likely to react with problems? I'd agree that it is impossible to know until it actually happens.

In technical diving, one should always be able to handle at least one catastrophic loss of gas by themselves in the case of buddy separation, as it does happen.

Isn't it in the rescue class where they stress that ensuring your own safety should be of highest priority?

Yes they do. But I don't want to get into the shortcomings or the lack of reality in rescue courses.

May be an old school way of thinking, but honestly for the situation to get to that point many things would've had to go wrong and my choosing to preserve air for me is the least of them.

So either they really failed to maintain their equipment, or they're diving well beyond their ability and skill.

Not necessarily: My Own Out of GAS Experience

Additionally, if the recipient costumes both their half and my half then it is guaranteed to not end well for both parties. If they consume the isolated and I still have gas at least I have a chance.

Maybe, unless they are able to grab on the reg in your mouth and you both basically fight for it and drown.

TL;DR: people out of gas will go for the reg in your mouth in panic situations. Everyone should be able to handle at least one failure by themselves, two in a pair. Buddy selection is important (technical diving isn't for everything. Heck, recreational diving isn't for everyone).

 

[RX8Bob]

I definitely agree buddy selection is definitely key. I also agree that rescue courses are woefully oversold and provide a false sense of competency imo but that's not for this discussion.

 

[Scuba_Nick27]

Hello. @Scuba_Nick27 You'll quickly find that divers have many views, and it's important to research, and make an informed decision, in regard to gear, and the applications/diving scenarios that the gear will be used. Of course, a lot of this is "Trial, and error." Example; I was certified on 17 Oct 1999 and bought my first tanks U.S. Divers "Double 80's." in December 1999. My first B.C.D. was a U.S. Divers "Seamaster." which at that time, was a top of the line product. Back inflate, Weight Integrated,(32 lbs.) 50 Lbs of lift, heavy duty thick shoulder harness, Etc,
It was designed to accommodate "Twin tanks." using nylon cam bands, and the hard internal back plate. It worked well, for less than a year. I logged approx 90 dives my first winter, and eventually the ABS plastic just broke nearly in half. I'm sure that the temperature differential was a factor, going from 28 degree water to the warmth of a house for 6 months. Ultimately, it was the sheer weight of the "Rig." being consistently used that broke it. (Live, and learn.) My other (2) "Sea Masters." diving single tanks lasted twenty years.
As, stated already in a couple of replies. I suggest not using a recreational B.C.D. for "Doubles."
When, I made the transition to BP/W I decided to buy Apeks gear. I had been eyeballing Apeks for about 8 years, or more. I purchased an "Aluminum Backplate." When, I took it out of the plastic bag, I was a little surprised? It seemed flimsy, and frail.(No offence, Apeks.) I could see the potential for it being easily bent. After looking it over....I just slide it back in the bag, and eventually gave it away.
Again, applications, and diving scenarios...I'm sure for many divers the "Aluminum." is perfect. (Just not for me.) I called and ordered (3) Apeks Stainless Steel Backplates, and when they arrived, I was extremely satisfied.
Last year, I had a little money kicking around, and bought (3) Apeks Black Ice B.C.D.'s You can order a "Twin cylinder kit." for them which is basically what I did 20 years ago. Overall, I don't think it's a good idea. Side note: They have never even seen water, because, when, I go diving I always reach for my BP/W (Probably selling them.)
At this point in time. "Twin Sets." with an isolation manifold, (For Redundancy.) and S.S. bands are widely used, and I would think holds the majority. I dove "Indies" for over 15 years. I won't go over that here, I get in enough "Hot water." on S.B. as it is.
Welcome to the board. There is a boundless fountain of information here,
Cheers.

Assembling Double Cylinders | Dive Gear Express®
HOW TO ASSEMBLE A SET OF DOUBLES - SDI | TDI | ERDI | PFI

Thankyou for the information sir

 

[John C. Ratliff]

generally, no for backmount. because in the case you have a failure and had to isolate, you turn the dive, so it doesn't matter if you can tell how much you have left, you either have enough (if you kept a sufficient reserve) or you don't.

Just to clarify, the failure would have to be if a type that would imparal the air supply (runaway free flow, LP hose break, blown HP SPG failure with air loss, etc.). If the regulator fails closed, so it supplies no air, simply switch to your other regulator or octopus and continue as the air supply is not compromised.

SeaRat

 

[John C. Ratliff]

I am, but **** happens, and in reality, very very few people know how they would react in a true ooa emergency. Simulate it all you want and figure out your RMV for high workload and such to figure out requisite air, but at the end of the day my intent is to go home. I'm not cutting off their air, I'm just protecting my half. If you've had a catastrophic failure where shutting down a post valve and or an isolator doesn't get you back to the surface (2 strikes), I'll give you half of mine and if you exhaust that, well then I'm sorry, you've had your 3 strikes.

Isn't it in the rescue class where they stress that ensuring your own safety should be of highest priority?

May be an old school way of thinking, but honestly for the situation to get to that point many things would've had to go wrong and my choosing to preserve air for me is the least of them.

So either they really failed to maintain their equipment, or they're diving well beyond their ability and skill.

Additionally, if the recipient costumes both their half and my half then it is guaranteed to not end well for both parties. If they consume the isolated and I still have gas at least I have a chance.


Yeah I'm no Mike Nelson.

In this case, because of your attitude toward your buddy, I would never be your buddy.

SeaRat