gas switch on Shearwater

OceanOpportunity · 15th April 2008, 19:30

Hey guys,

Quick Q: when switching dil on a Shearwater, does the computer assume that you are flushing the loop with the diluent? Naturally, this doesnt matter if you are using multiple heliox mixes, but if switching from air to heliox any nitrogen remaining in the loop would naturally factor in to things.

I 'grew up' on the CCR2000, which accounted for residual N2 in the loop.

Just looking for clarification

Cheers,
ML

Mark Chase · 15th April 2008, 19:48

Quote: (Originally Posted by OceanOpportunity)

Hey guys,

Quick Q: when switching dil on a Shearwater, does the computer assume that you are flushing the loop with the diluent? Naturally, this doesnt matter if you are using multiple heliox mixes, but if switching from air to heliox any nitrogen remaining in the loop would naturally factor in to things.

I 'grew up' on the CCR2000, which accounted for residual N2 in the loop.
Just looking for clarification

Cheers,
ML

How did it do this?

I would have thaught if your switching diluients mid dive you would have to do a proper flush on the switch or else what the point?

If your on the way up you dont need dill so unless you flush your not realy gas switching. On the way down is there any point in gas switching?

It seems an odd thing to me.

As far as the Sherwater is concerned; if its plumbed in it will react to PP02 only so if you tell it you have gas switched and didnt flush i cant see it being acurate anymore.

ATB

Mark

OceanOpportunity · 15th April 2008, 21:26

This is what I thought..thanks for clarifying.

The theory behind the 2000 electronics was based on the premise that 2 onboard diluents were carried at all times. Typically air, and some other mix (tri- or heliox). When diving air dil to a target switch depth, then switching to heliox, you are effectively locking in the PN2 (equivalent narcotic depth). While adding heliox during the rest of the descent, the loop contains a trimix, so you reap the deco benefits (if any depending on the profile) of a less helium rich gas. The computer would read the PO2 from the cells, and use a calculated PN2 based on your dil 1, setpoint, and switch depth.

Nice feature in principle, but it made me weary since there were no cells sniffing the rest of the gas (he, n2, or otherwise). Might be nice for someone to work He cells into the mix down the road for this specific purpose.

ML

David Pye · 15th April 2008, 21:44

Nice idea if you're the perfect rebreather diver I guess, but if you have leaky lips, or need to clear your mask etc, I can't see the idea being quite so smart then!

Mark Chase · 16th April 2008, 08:41

I would have thaught the major deco benifit would be on ascent. During that phase you'd need to flush.

Surley it would have to be a very deep dive to see any deco advantage gas switching on decent.

It sounds likle a complex bit of additional programig that has no validation and a large error potential.

Have you noticed any benifit on your unit in comparison to others?

ATB

Mark

OceanOpportunity · 16th April 2008, 13:22

The 2000, as I understand it, was originally designed with VERY deep diving in mind. It was used for several sub-150m dives early on..before anyone else was doing this stuff (say early 1990's).

It had its ups and downs, like any unit. I liked that it had BMCL (I'm a huge proponent of this), and effectively the same loop characteristics as the MkX rigs. Its computer had some great features. It had an '@ + 5' feature which was a look ahead at your no-deco-limit where if you stayed at your depth for another 5 minutes, would your NDL be longer or shorter. This was a crude meausre of whether you were ongassing or ofgassing...nice for taking advantage of multi-level dive profiles on the fly. This is the one feature I miss on my current unit. The electronics took way too much power (4-D cells) which was a downside. It used heavy duty wet-connects like those used on ROV's...very robust and worry-free.

all in all, the unit itself wasn't perfect (none of them are), but had some innovative tricks that were way ahead of its time.

I'm not diving it anymore because I realized some shortcomings with the loop construction, and it weighed way too much at 60+ pounds

bgpartri · 16th April 2008, 15:26

A gas switch on a CCR 2000 would also require a flush. I think that you are confusing two issues.

At the time, both the CCR 2000 and the MK5 supported "constant PN2." On the CCR 2000, that was implemented by having two diluent tanks, typically air and heliox. You could descend to what you determined was an optimal EAD for narcosis, then switch from your air dil to your heliox. For the rest of the way down, no N2 would be added, so your PN2 would stay constant.

I'm not as familiar with the MK5, but I was told that you could do the same thing on it. As I understand it, that is the way they dived it on the Wakulla 2 project.

Obviously excessive mask clearing could change the mix without the computer knowing, but it seemed pretty cool at the time.

Flushes were a different thing. There was a configuration parameter that you set pre-dive to tell the computer whether you were going to flush when you switched back to the air dil on ascent. Back then, flushing to air on the ascent was a common practise.

I agree, it was an amazing machine in its time. It had great WOB and very capable electronics. The downside was that it was complex and heavy. My experience on the CCR 2000 was one of things that led to my current views on simplicity and "clear mental models."

By the way, Dan Wible is still around. He came down to the dive site to say hello when Paul was teaching his rEvo course in Washington a couple of months ago.

Bruce

**NEDIVER** · 17th April 2008, 02:59

Has anyone ever explored the possibility of taking the 4th cell and incorporating a dual oxygen/helium cell that could constantly analyze the amount of Nitrogen in the loop and plug that into a program?

I know this may be a large undertaking (and expensive one, considering the dual oxygen/helium cell is $899) but it may be beneficial to the longer deeper dives.

After all if my understanding of gas is correct, unlike mixing a gas mixture in a tank, where all the parts = 100%, in a loop, you only have two parts = 100%. What I mean by this is by addition of O2 you reduce the volume of the other gas, in the case of Trimix diluent, you are reducing the volume of the diluent. O2 percent goes up because it is additive, Nitrogen goes down AND Helium % is reduced as well. (please let me know if my thinking is wrong)

Does the current computer systems figure in this loss of He % or are they running on the constant percentage model (it may be close enough to do so).

Here is a link of a Sensor that could be used as a fourth cell if the software supported it. MixCheq He cell

the idea may get eaten up, but I thought I would through it out there for those smarter than I to contemplate.

OceanOpportunity · 17th April 2008, 13:04

Quote: (Originally Posted by NEDIVER)

Has anyone ever explored the possibility of taking the 4th cell and incorporating a dual oxygen/helium cell that could constantly analyze the amount of Nitrogen in the loop and plug that into a program?

I'm sure it has been a consideration for the electronics folks, although I can't speak for them. Maybe Bruce has some insight...

Personally, it is something I'd like to see down the road. It's really only useful for multiple diluent use (on descent), but profile pending, there are definitely advantages to the PN2/END 'setpoint' concept as was available in the ccr2000. In theory the He sensor should be easy enough to do..basic Dalton's law factored in to the electronics, which is already used for PN2 or PHe calcs independently as single varibales. There may be issues with the He cells under high humidity (jsut guessing, I'm not an expert on cells by any means).

Now, I know someone's bound to say 'WTF do we need that for?'....well, 10 years ago most on this thread said that about Rebreather's in general.

I'd like a CO2 monitor first though!!!

15th April 2008, 19:30	#1 (permalink)
OceanOpportunity for a world of water Current Rebreather/s: Other CCR Dolphin Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Other CCR Dolphin Home Build Join Date: Nov 2006 Location: Providence, RI USA Posts: 541	gas switch on Shearwater Hey guys, Quick Q: when switching dil on a Shearwater, does the computer assume that you are flushing the loop with the diluent? Naturally, this doesnt matter if you are using multiple heliox mixes, but if switching from air to heliox any nitrogen remaining in the loop would naturally factor in to things. I 'grew up' on the CCR2000, which accounted for residual N2 in the loop. Just looking for clarification Cheers, ML __________________ Michael Lombardi Oceans of Opportunity www.oceanopportunity.com Elected Director, Society for Human Performance in Extreme Environments MN'07, The Explorers Club Project Manager, Diving a Dream
(Offline)

15th April 2008, 19:48	#2 (permalink)
Mark Chase I go down for ages Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Jan 2005 Location: Kent Posts: 2,693	Re: gas switch on Shearwater Quote: (Originally Posted by OceanOpportunity) Hey guys, Quick Q: when switching dil on a Shearwater, does the computer assume that you are flushing the loop with the diluent? Naturally, this doesnt matter if you are using multiple heliox mixes, but if switching from air to heliox any nitrogen remaining in the loop would naturally factor in to things. I 'grew up' on the CCR2000, which accounted for residual N2 in the loop. Just looking for clarification Cheers, ML How did it do this? I would have thaught if your switching diluients mid dive you would have to do a proper flush on the switch or else what the point? If your on the way up you dont need dill so unless you flush your not realy gas switching. On the way down is there any point in gas switching? It seems an odd thing to me. As far as the Sherwater is concerned; if its plumbed in it will react to PP02 only so if you tell it you have gas switched and didnt flush i cant see it being acurate anymore. ATB Mark __________________ Is it supposed to make that noise ? I took my unit to the dive shop and demanded they bolt on every thing that would fit. Join my elite diving teem and get a Tshirt "Doing It Chasey"Hammerhead Eccr Advanced Diving System
(Online)

15th April 2008, 21:26	#3 (permalink)
OceanOpportunity for a world of water Current Rebreather/s: Other CCR Dolphin Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Other CCR Dolphin Home Build Join Date: Nov 2006 Location: Providence, RI USA Posts: 541	Re: gas switch on Shearwater This is what I thought..thanks for clarifying. The theory behind the 2000 electronics was based on the premise that 2 onboard diluents were carried at all times. Typically air, and some other mix (tri- or heliox). When diving air dil to a target switch depth, then switching to heliox, you are effectively locking in the PN2 (equivalent narcotic depth). While adding heliox during the rest of the descent, the loop contains a trimix, so you reap the deco benefits (if any depending on the profile) of a less helium rich gas. The computer would read the PO2 from the cells, and use a calculated PN2 based on your dil 1, setpoint, and switch depth. Nice feature in principle, but it made me weary since there were no cells sniffing the rest of the gas (he, n2, or otherwise). Might be nice for someone to work He cells into the mix down the road for this specific purpose. ML __________________ Michael Lombardi Oceans of Opportunity www.oceanopportunity.com Elected Director, Society for Human Performance in Extreme Environments MN'07, The Explorers Club Project Manager, Diving a Dream
(Offline)

15th April 2008, 21:44	#4 (permalink)
David Pye CK#69 Current Rebreather/s: Classic Kiss Other Rebreather/s: Join Date: May 2006 Location: Newcastle Upon Tyne Posts: 174	Re: gas switch on Shearwater Nice idea if you're the perfect rebreather diver I guess, but if you have leaky lips, or need to clear your mask etc, I can't see the idea being quite so smart then!
(Online)

16th April 2008, 08:41	#5 (permalink)
Mark Chase I go down for ages Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Jan 2005 Location: Kent Posts: 2,693	Re: gas switch on Shearwater I would have thaught the major deco benifit would be on ascent. During that phase you'd need to flush. Surley it would have to be a very deep dive to see any deco advantage gas switching on decent. It sounds likle a complex bit of additional programig that has no validation and a large error potential. Have you noticed any benifit on your unit in comparison to others? ATB Mark __________________ Is it supposed to make that noise ? I took my unit to the dive shop and demanded they bolt on every thing that would fit. Join my elite diving teem and get a Tshirt "Doing It Chasey"Hammerhead Eccr Advanced Diving System
(Online)

16th April 2008, 13:22	#6 (permalink)
OceanOpportunity for a world of water Current Rebreather/s: Other CCR Dolphin Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Other CCR Dolphin Home Build Join Date: Nov 2006 Location: Providence, RI USA Posts: 541	Re: gas switch on Shearwater The 2000, as I understand it, was originally designed with VERY deep diving in mind. It was used for several sub-150m dives early on..before anyone else was doing this stuff (say early 1990's). It had its ups and downs, like any unit. I liked that it had BMCL (I'm a huge proponent of this), and effectively the same loop characteristics as the MkX rigs. Its computer had some great features. It had an '@ + 5' feature which was a look ahead at your no-deco-limit where if you stayed at your depth for another 5 minutes, would your NDL be longer or shorter. This was a crude meausre of whether you were ongassing or ofgassing...nice for taking advantage of multi-level dive profiles on the fly. This is the one feature I miss on my current unit. The electronics took way too much power (4-D cells) which was a downside. It used heavy duty wet-connects like those used on ROV's...very robust and worry-free. all in all, the unit itself wasn't perfect (none of them are), but had some innovative tricks that were way ahead of its time. I'm not diving it anymore because I realized some shortcomings with the loop construction, and it weighed way too much at 60+ pounds __________________ Michael Lombardi Oceans of Opportunity www.oceanopportunity.com Elected Director, Society for Human Performance in Extreme Environments MN'07, The Explorers Club Project Manager, Diving a Dream
(Offline)

16th April 2008, 15:26	#7 (permalink)
bgpartri Rebreather Zealot Current Rebreather/s: Megalodon Other Rebreather/s: Inspiration Classic Sport Kiss Classic Kiss Titan Join Date: Apr 2005 Location: Vancouver, Canada Posts: 412	Re: gas switch on Shearwater A gas switch on a CCR 2000 would also require a flush. I think that you are confusing two issues. At the time, both the CCR 2000 and the MK5 supported "constant PN2." On the CCR 2000, that was implemented by having two diluent tanks, typically air and heliox. You could descend to what you determined was an optimal EAD for narcosis, then switch from your air dil to your heliox. For the rest of the way down, no N2 would be added, so your PN2 would stay constant. I'm not as familiar with the MK5, but I was told that you could do the same thing on it. As I understand it, that is the way they dived it on the Wakulla 2 project. Obviously excessive mask clearing could change the mix without the computer knowing, but it seemed pretty cool at the time. Flushes were a different thing. There was a configuration parameter that you set pre-dive to tell the computer whether you were going to flush when you switched back to the air dil on ascent. Back then, flushing to air on the ascent was a common practise. I agree, it was an amazing machine in its time. It had great WOB and very capable electronics. The downside was that it was complex and heavy. My experience on the CCR 2000 was one of things that led to my current views on simplicity and "clear mental models." By the way, Dan Wible is still around. He came down to the dive site to say hello when Paul was teaching his rEvo course in Washington a couple of months ago. Bruce __________________ http://www.shearwaterresearch.com Good judgment comes from experience. Experience comes from bad judgment.
(Offline)

17th April 2008, 02:59	#8 (permalink)
NEDIVER Sic Semper Tyrannis Current Rebreather/s: Evolution Other Rebreather/s: Join Date: Jan 2008 Location: Nashua, NH Posts: 138	Re: gas switch on Shearwater Has anyone ever explored the possibility of taking the 4th cell and incorporating a dual oxygen/helium cell that could constantly analyze the amount of Nitrogen in the loop and plug that into a program? I know this may be a large undertaking (and expensive one, considering the dual oxygen/helium cell is $899) but it may be beneficial to the longer deeper dives. After all if my understanding of gas is correct, unlike mixing a gas mixture in a tank, where all the parts = 100%, in a loop, you only have two parts = 100%. What I mean by this is by addition of O2 you reduce the volume of the other gas, in the case of Trimix diluent, you are reducing the volume of the diluent. O2 percent goes up because it is additive, Nitrogen goes down AND Helium % is reduced as well. (please let me know if my thinking is wrong) Does the current computer systems figure in this loss of He % or are they running on the constant percentage model (it may be close enough to do so). Here is a link of a Sensor that could be used as a fourth cell if the software supported it. MixCheq He cell the idea may get eaten up, but I thought I would through it out there for those smarter than I to contemplate. __________________ -Tom- "slow is smooth, and smooth is fast" TM "Insanity is repeating the same thing over and over again, expecting different results" Albert Einstein
(Offline)

17th April 2008, 13:04	#9 (permalink)
OceanOpportunity for a world of water Current Rebreather/s: Other CCR Dolphin Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Other CCR Dolphin Home Build Join Date: Nov 2006 Location: Providence, RI USA Posts: 541	Re: gas switch on Shearwater Quote: (Originally Posted by NEDIVER) Has anyone ever explored the possibility of taking the 4th cell and incorporating a dual oxygen/helium cell that could constantly analyze the amount of Nitrogen in the loop and plug that into a program? I'm sure it has been a consideration for the electronics folks, although I can't speak for them. Maybe Bruce has some insight... Personally, it is something I'd like to see down the road. It's really only useful for multiple diluent use (on descent), but profile pending, there are definitely advantages to the PN2/END 'setpoint' concept as was available in the ccr2000. In theory the He sensor should be easy enough to do..basic Dalton's law factored in to the electronics, which is already used for PN2 or PHe calcs independently as single varibales. There may be issues with the He cells under high humidity (jsut guessing, I'm not an expert on cells by any means). Now, I know someone's bound to say 'WTF do we need that for?'....well, 10 years ago most on this thread said that about Rebreather's in general. I'd like a CO2 monitor first though!!! __________________ Michael Lombardi Oceans of Opportunity www.oceanopportunity.com Elected Director, Society for Human Performance in Extreme Environments MN'07, The Explorers Club Project Manager, Diving a Dream
(Offline)

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