Question CCR, SM diving, and proper weighting?

[kierentec]

A lot of good points already made. One of my concerns with this weighting philosophy is what if you have to donate gas to a teammate? Likely on CCR? Not very, but a teammate suffering a CO2 hit will likely need all of the gas in the cave….

 

[mr_v]

@mr_v you are using the mass of the gas not the inherent buoyancy of the tank. 4.8lbs at 500psi not 2.8.

You're right, I fudged up the numbers. It should be closer to 3.5#: -0.7 on start and 2.8 at close to 500 PSI. How did you get 4.8lbs?

The most concerning thing for me is how much they are relying on flooding a Sidewinder which has very little floodable volume in it, essentially it's barely more than the loop hoses themselves and to flood the inhale hose is going to take some acrobatics. The sorb is put directly in the canisters so there is not a lot of airspace inside the canisters themselves.

Biggest concern? What if you bailed out for reasons other than a rebreather malfunction? Now you've flooded a good unit.

 

[stuartv]

You're right, I fudged up the numbers. It should be closer to 3.5#: -0.7 on start and 2.8 at close to 500 PSI. How did you get 4.8lbs?


Biggest concern? What if you bailed out for reasons other than a rebreather malfunction? Now you've flooded a good unit.

Any unit that can't handle being flooded probably should never go in the water. Worst case should be replacing O2 sensors - if it got REALLY flooded and stayed that way for a while.

And the discussion is only about flooding your unit if you have to, to keep from corking. That's your last resort and if things go so badly that you have to do that, and it works, then, well, I wouldn't be complaining about having to replace some O2 sensors if it came to that.

 

[mr_v]

I should have used "working unit" instead of "good unit" in the context above. Either way, I fail to see a significant benefit of the "new" method. Perhaps there is some middle ground where you are still overweight in water but not by a manageable amount. I am still learning so that is my 2 cents with 50% off ;-)

 

[tbone1004]

You're right, I fudged up the numbers. It should be closer to 3.5#: -0.7 on start and 2.8 at close to 500 PSI. How did you get 4.8lbs?


Biggest concern? What if you bailed out for reasons other than a rebreather malfunction? Now you've flooded a good unit.

.08 lbs/cf of air*72cf in tank*2500psi used/3000psi rated pressure=4.8lbs of gas consumed

 

[lermontov]

my concern is buoyancy if you have take the unit off - im yet to experiment but i alway wonder how much weight id need on me to not get pinned to an overhead

 

[rjack321]

my concern is buoyancy if you have take the unit off - im yet to experiment but i alway wonder how much weight id need on me to not get pinned to an overhead

Why would you remove your unit? Partially removing your unit potentially has its place in extreme exploration scenarios but...

There have been numerous fatalities from exactly this. The fatality in Ginnie springs and the double fatality in Eagle's Nest are both directly attributable to divers removing their units. The former flooded due to burping O2, the latter led to one diver being crazy buoyant which ended up killing him and his buddy as they attempted a BO exit together.

There are basically zero established protocols for unit removals so beware.

 

[lermontov]

Why would you remove your unit? Partially removing your unit potentially has its place in extreme exploration scenarios but...

There have been numerous fatalities from exactly this. The fatality in Ginnie springs and the double fatality in Eagle's Nest are both directly attributable to divers removing their units. The former flooded due to burping O2, the latter led to one diver being crazy buoyant which ended up killing him and his buddy as they attempted a BO exit together.

There are basically zero established protocols for unit removals so beware.

thinking mostly from situation where you got entangled in wreck ( net, wires etc) than a tight cave, where you couldnt free yourself and your buddy is unable to assist (or if your solo)

 

[mr_v]

thinking mostly from situation where you got entangled in wreck ( net, wires etc) than a tight cave, where you couldnt free yourself and your buddy is unable to assist (or if your solo)

That's a "do not do" from the first step. Simply avoid scenarios where you can recklessly put yourself and others in danger. There is really no reason to remove your unit.

 

[lermontov]

That's a "do not do" from the first step. Simply avoid scenarios where you can recklessly put yourself and others in danger. There is really no reason to remove your unit.

you response is a tad patronising- lets start with removing the word 'recklessly' nobody deliberately puts themselves in a life or death situation but sometimes things go wrong and it happens, and if it does you need a plan and that plan as a last resort may involve removing a unit.

I know people that have had to abandon their OC gear to escape an entanglement using a ccr doesnt make you immune from it.

Wouldn't you rather try it out in a controlled situation to see what it entails rather than find yourself in that situation and not know?