Rebreather designs and buoyancy control strategies

[Dsix36]

I have several years on various rebreathers and a few years on the rEvo in particular. I have, and still do, use my wing, loop volume, and drysuit all for buoyancy. What I use at any given time will be dictated by multiple things. These can be the dive profile, my needed trim at the moment, the terrain just ahead of me, and it will change at any time as I deem necessary and must beneficial to me.

When I reach the surface, the only form of buoyancy is ALWAYS the wing if I feel the need to be further out of the water than I already am. I DO NOT like to remove my DSV until I am safely on the boat and waste a lot of O2 making damn sure to have a safe loop to breathe.

I have been forced to speak on the surface and have removed the DSV without closing to blurt out a quick answer on more than one occassion and my loop did not instantly empty as some have stated. It still contained enough gas to breathe when I stuck the DSV back in my gob. it is extremely easy to over vent on the surface and feel your lungs turn inside out trying to get a breathe if you are not careful and tolerate a bit of "chipmunk cheeks".

 

[oya]

.

You're 41 according to your profile? Just thinking: I was diving a rebreather when you were two years old and still sucking a binkie. You were in elementary school when I did my first Doria trip. Maybe, just maybe, I'm competent

Maybe.

Maybe you're suggesting, with an air of authority that someone which may mislead someone who doesn't know better, that the right way of doing things is an outdated and silly practice that leaves people dangerously underweighted for decompression diving.

Maybe.

Yeah, I'm 41. But I've dived a lot and managed to learn from some of the best in the sport. I don't think I'm the greatest, but I'm pretty good. A newbie in a lot of ways; very experienced in others. Always trying to get better.

But according to your profile you've only 21 and got less than 100 dives. And I have no idea who you are. So forgive me for not ceding to your superior experience and ability.

Planning to start a decompression dive underweighted if the it hits the fan might kill you. Suggesting otherwise is dumb.

 

[St John the Diver]

Maybe.

Maybe you're suggesting, with an air of authority that someone which may mislead someone who doesn't know better, that the right way of doing things is an outdated and silly practice that leaves people dangerously underweighted for decompression diving.

Maybe.

Yeah, I'm 41. But I've dived a lot and managed to learn from some of the best in the sport. I don't think I'm the greatest, but I'm pretty good. A newbie in a lot of ways; very experienced in others. Always trying to get better.

But according to your profile you've only 21 and got less than 100 dives. And I have no idea who you are. So forgive me for not ceding to your superior experience and ability.

Planning to start a decompression dive underweighted if the it hits the fan might kill you. Suggesting otherwise is dumb.

Nobody is suggesting diving underweighted.

The thing to remember, truly, is that a rebreather diver you have a suite of three variable volume systems that impact bouyancy. Wings, suit, and counterlungs. They need to be balanced one against the other. Diving absolute minimum CL volume isn't smart, as it increases WOB on every rig. Optimal CL volume is a bit more than that. And the "range" of optimal CL volume is enough for use as a fine bouyancy control device.

EVERY rebreather diver I've ever seen surfaces slightly positive. And EVERY one will go negative to some extent or another if they remove the DSV workout closing it unless they add gas to "something" before they do so. For me, that's where I use my wings. And it's generally the first and only time I've used my wings on my dive. And a task saturated inexperienced rebreather diver (like the victim here) could VERY easially make a lethal error at the surface.


Adding a point to learn from: Carefully sensing bouyancy is a low-level way to monitor PP02. If depth is constant, a change in bouyancy from neutral towards negative means you're metabolizing 02 without it being added. Diving the KISS and later the rEvo, I was finding myself maintaining neutral bouyancy with the 02 manual add valve and cross checking to PP02. It never varied. We did the same thing in the old analog Mark-15 system where the only set point was 0.7 (using Rev-G electronics with a normal calibration). We left the rig running but maintained 1.2 manually (flying above setpoint) and bouyancy sensing was a very useful tool for PP02 maintenance. Then we began doing "blind drills" (flying without monitoring) by flushing out at depth, calculating PP02 of the diluent, making a swim at constant depth, and simply maintaining neutral bouyancy with manual 02 additions. With a safety diver watching our displays we were able to maintain that PP02 for an hour "blind".

There's always more to learn. And for sure there's more than you (or I) have learned so far.

 

[Patoux01]

[snip]
There was a diver who died on the Doria a while back who was wing-centric and not suit-centric for bouyancy.
[snip]

Okay, wing is bad, then close and inflate your suit 'till the OPV pops on the surface is what you should be teaching. (that's another level of stupidity, as you still have 2 things to do instead of just pushing one button)

Lots of funny trends we can observe on ccr divers which make very little sense for people that don't use them (because I doubt I'm the only one)...

 

[oya]

Then we began doing "blind drills" (flying without monitoring) by flushing out at depth, calculating PP02 of the diluent, making a swim at constant depth, and simply maintaining neutral bouyancy with manual 02 additions. With a safety diver watching our displays we were able to maintain that PP02 for an hour "blind".

Yeah.

Was this for fun, or was it a drunken dare?

Dear anyone and everyone-
Don't do this.

 

[St John the Diver]

I have several years on various rebreathers and a few years on the rEvo in particular. I have, and still do, use my wing, loop volume, and drysuit all for buoyancy. What I use at any given time will be dictated by multiple things. These can be the dive profile, my needed trim at the moment, the terrain just ahead of me, and it will change at any time as I deem necessary and must beneficial to me.

When I reach the surface, the only form of buoyancy is ALWAYS the wing if I feel the need to be further out of the water than I already am. I DO NOT like to remove my DSV until I am safely on the boat and waste a lot of O2 making damn sure to have a safe loop to breathe.

I have been forced to speak on the surface and have removed the DSV without closing to blurt out a quick answer on more than one occassion and my loop did not instantly empty as some have stated. It still contained enough gas to breathe when I stuck the DSV back in my gob. it is extremely easy to over vent on the surface and feel your lungs turn inside out trying to get a breathe if you are not careful and tolerate a bit of "chipmunk cheeks".

Yeah.

Was this for fun, or was it a drunken dare.

Dear anyone and everyone-
Don't do this.

It was a military necessity skill. There are times when you do not want to lose your loop. As in "we weren't issued bailout" and had no choice.

Will Smithers came up with a breath counting blind bailout method that worked as well. He figured out how many breaths it took to drop the loop from "x" to "y" at different depths, with a loop that had been flushed with diluent turns out that swimming harder you breath faster less workload means to breath slower. He experimented and figured out that the same number of breaths when breathing normally dropped the PP02 by the same amount no matter the workload. It worked. You just need to know what you're doing. So few really do.


So, with all that said, weren't you taught how to do blind SCC drills in training? It's a basic survival skill for the advanced rebreather diver.

 

[St John the Diver]

Okay, wing is bad, then close and inflate your suit 'till the OPV pops on the surface is what you should be teaching. (that's another level of stupidity, as you still have 2 things to do instead of just pushing one button)

Lots of funny trends we can observe on ccr divers which make very little sense for people that don't use them (because I doubt I'm the only one)...

Reducing a complex calculus to the absurd.

That's not at all what I'm saying, or suggesting. Be smart enough to understand nuances.

 

[oya]

But with that said, weren't you taught how to do blind SCC drills in training? It's a basic survival skill for the advanced rebreather diver.

Yes. Years ago.

No. It's and outdated skill that is no longer in the curriculum because it's more dangerous than anything.

The modern philosophy is more along the lines of: "Have enough bailout. Even if you need to use your wing to carry it."

 

[St John the Diver]

Yes. Years ago.

No. It's and outdated skill that is no longer in the curriculum because it's more dangerous than anything.

The modern philosophy is more along the lines of: "Have enough bailout. Even if you need to use your wing to carry it."

Not so. It's a mandatory part of advanced training. There's no need to use precious bailout to get back to the anchor line in many cases. And when you really dive deep, you're not going to be carrying as much bailout as you might like. Do many 400 footers lately? Come talk to me when it's routine for you. You might want to have those expert level skills in your bag when you're at one end of the wreck and the mooring is at the other end of the wreck. You can make it back to the mooring on your loop "piece of cake" if you know how to do a SCC drill. Save that bailout for ascent.

 

[oya]

It's a mandatory part of advanced training.

I assume, with your being so well versed with the standards you're an instructor?

revo, probably, knowing it as well?