DrySuitDave
Contributor
Does anyone use a Cochran Gemini P02 dive computer? I am still trying to figure out how to deploy it.....
Cochran Gemini for CCR?
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DrySuitDave
Contributor
Mine is called the 2 p02 2 fo2 version, so I guess that means it can be used for semi closed circuit f02 rebreathers like the Dragers, or used for fully closed circuit rebreathers like my Inspiration based upon p02.
I THINK I am supposed to set the computer to switch over to a predetermined p02 based upon depth. Ok, so let's say I use a p02 set point of .7 for the bottom, and 1.1 or 1.2 for less than 10 feet. Well, I don't switch over to the bottom p02 setting till I am at the bottom, but if we know the depth in advance, what if I decide to go to a different area?
I wish it was as easy to change the p02 setpoint on the computer to match my controller setpoint than have to change my controller set points to match the computer.
Thoughts?
I THINK I am supposed to set the computer to switch over to a predetermined p02 based upon depth. Ok, so let's say I use a p02 set point of .7 for the bottom, and 1.1 or 1.2 for less than 10 feet. Well, I don't switch over to the bottom p02 setting till I am at the bottom, but if we know the depth in advance, what if I decide to go to a different area?
I wish it was as easy to change the p02 setpoint on the computer to match my controller setpoint than have to change my controller set points to match the computer.
Thoughts?
a) Shouldn't you use your higher set point on the bottom?
b) The setpoints you have chosen for above 10 ft are > ambient so your be constantly venting O2 as the unit will never get to the setpoint (thats why you have a low setpoint)
c) Buy a computer thats designed for CCR diving and is manually switched or has real time loop O2 cell (Nexus, or VR3 spring to mind), not one designed by a marketing deprtment who dont understand CC.
I can think of many reasons why you will not be switching setpoints based on depth. Wanting to push up the PPO2 for deco, taking an air break after a long O2 hang etc. The Demini just isn't suitable if it auto swithces
b) The setpoints you have chosen for above 10 ft are > ambient so your be constantly venting O2 as the unit will never get to the setpoint (thats why you have a low setpoint)
c) Buy a computer thats designed for CCR diving and is manually switched or has real time loop O2 cell (Nexus, or VR3 spring to mind), not one designed by a marketing deprtment who dont understand CC.
I can think of many reasons why you will not be switching setpoints based on depth. Wanting to push up the PPO2 for deco, taking an air break after a long O2 hang etc. The Demini just isn't suitable if it auto swithces
I have my Gemini set to switch at 20ft from 0.7 to 1.0. Even if you do not switch your Inspiration setpoint until you are on the bottom, you are still erroring on the side of caution with regard to decompression obligation and O2 exposure.
Also, I talked to Cochran recently, and they are set to have their CCR integrated PO2 computer available early 2003. As usual, they will be offering their unbeatable upgrade program.
For what it is worth, I went on a recent trip with a group of divers who were diving both Inspirations and Biomarine 15.5s. They each had VR3s and Cochrans. All four of the divers preferred the Cochran over the VR3 in spite of the lack of O2 monitoring. These were divers who have been diving CCR for over 10 years! From what I could gather, it was the Cochran algorithm they liked.
Also, I talked to Cochran recently, and they are set to have their CCR integrated PO2 computer available early 2003. As usual, they will be offering their unbeatable upgrade program.
For what it is worth, I went on a recent trip with a group of divers who were diving both Inspirations and Biomarine 15.5s. They each had VR3s and Cochrans. All four of the divers preferred the Cochran over the VR3 in spite of the lack of O2 monitoring. These were divers who have been diving CCR for over 10 years! From what I could gather, it was the Cochran algorithm they liked.
I use a cochran commander 2 Po2 / 2 fo2..
I start with a set point of 1.3 (even though on decending I'm a bit lower than this but I have a fairly fast decent so its close enough -plus with the typical 5 minute prebreathe at the surface you are in better shape than the computer thinks anyway and doesn't really alter my deco obligaions(in fact in warm clear water where I'm dropping freely I may have a Po2 as high as 1.6 at depth(usually when I'm stuck using Air as a diluent) - but usually 1.4 or 1.5 is my max).. I set the deco threshold usually at 15 minutes so If I'm not at depth longer than 15 mins it doesn't switch set points, I set my deco setpoint at a lower PO2 than I'm actually diving(and more han makes u for the slight error during decent). I'll set it to swicth at 20ft for dives that I know I'll be comming up an anchor line so only that stop is increased.. If I'm cruising a reef, I'll lower my setpoint to 1.0 @ 40 ft since if I'm changing depths alot I'll fly it manually keeping a minimal setpoint of 1.0 when I go shallower, so I can drop right back to 40 ft if I go over a coral head, If I drop deeper it will use the 1.3 again..
(with the controller set at .7)
The VR3 Po2 monitoring responds slowly anyway, so its no better than me assuming a higher PO2 unless I had a long delay. A straight decent to 20 ft takes 10 or 15 seconds and you are already at a 1.1 using the original setpoint of .7, , in a few more secons I'm down to 30ft and if I started at absolute minimum loop at the surface (highly unlikely) I'm already around 1.2 and maybe 30 seconds into the dive....
I start with a set point of 1.3 (even though on decending I'm a bit lower than this but I have a fairly fast decent so its close enough -plus with the typical 5 minute prebreathe at the surface you are in better shape than the computer thinks anyway and doesn't really alter my deco obligaions(in fact in warm clear water where I'm dropping freely I may have a Po2 as high as 1.6 at depth(usually when I'm stuck using Air as a diluent) - but usually 1.4 or 1.5 is my max).. I set the deco threshold usually at 15 minutes so If I'm not at depth longer than 15 mins it doesn't switch set points, I set my deco setpoint at a lower PO2 than I'm actually diving(and more han makes u for the slight error during decent). I'll set it to swicth at 20ft for dives that I know I'll be comming up an anchor line so only that stop is increased.. If I'm cruising a reef, I'll lower my setpoint to 1.0 @ 40 ft since if I'm changing depths alot I'll fly it manually keeping a minimal setpoint of 1.0 when I go shallower, so I can drop right back to 40 ft if I go over a coral head, If I drop deeper it will use the 1.3 again..
(with the controller set at .7)
The VR3 Po2 monitoring responds slowly anyway, so its no better than me assuming a higher PO2 unless I had a long delay. A straight decent to 20 ft takes 10 or 15 seconds and you are already at a 1.1 using the original setpoint of .7, , in a few more secons I'm down to 30ft and if I started at absolute minimum loop at the surface (highly unlikely) I'm already around 1.2 and maybe 30 seconds into the dive....
OP
DrySuitDave
Contributor
Mike,
I have noticed that if my p02 setpoint is 1.3 or higher, it injects too frequently when 10 feet or shallower. I was told to keep my p02 at bottom around .7 to reduce my oxygen toxicity clock and CNS obligations for multi dives especially the multiday stuff I have coming up.
Once ascending, the p02 is changed to the high setpoint to reduce nitrogen loading and help offgas, then when nearing 10 feet, if not hanging out for a brief stop, anything 10 feet or shallower switches back to a lower setpoint to keep the solenoid relatively inactive.
Joe, I have no planned deco stuff, but I will definately try to digest your post. I too am waiting for the Gemini Lifeguard model that will have realtime p02 connectivity with the Inspiration.
I just picked up a Cochran computer holder mounted on a plastic slate with an integral retractor system to it since the wrist thing had a tendency to hangup when putting my left arm in through the counterlung space when saddling up.
This weekend I will be out for several days at San Nicholas in an attempt to inaugurate myself in the lobster death squad. I picked up a NiteRider HID hand mount system with a hip mounted compact NiMH battery for a 4 hour burn time, so it will be interesting to see how having two hands free works on those huge bugs I always catch in my mind.
I got an Aqualung LPO second stage to cannibalize parts into Bob Howel''s ADV if he ever answers my e-mail order that is!
Who was telling me the Aussie Sea Hornet din valves will work on OMS cylinders without any Inspiration fairing flexing or modification? I don't want any local boats to freak trying to fill factory AP tanks.
I have noticed that if my p02 setpoint is 1.3 or higher, it injects too frequently when 10 feet or shallower. I was told to keep my p02 at bottom around .7 to reduce my oxygen toxicity clock and CNS obligations for multi dives especially the multiday stuff I have coming up.
Once ascending, the p02 is changed to the high setpoint to reduce nitrogen loading and help offgas, then when nearing 10 feet, if not hanging out for a brief stop, anything 10 feet or shallower switches back to a lower setpoint to keep the solenoid relatively inactive.
Joe, I have no planned deco stuff, but I will definately try to digest your post. I too am waiting for the Gemini Lifeguard model that will have realtime p02 connectivity with the Inspiration.
I just picked up a Cochran computer holder mounted on a plastic slate with an integral retractor system to it since the wrist thing had a tendency to hangup when putting my left arm in through the counterlung space when saddling up.
This weekend I will be out for several days at San Nicholas in an attempt to inaugurate myself in the lobster death squad. I picked up a NiteRider HID hand mount system with a hip mounted compact NiMH battery for a 4 hour burn time, so it will be interesting to see how having two hands free works on those huge bugs I always catch in my mind.
I got an Aqualung LPO second stage to cannibalize parts into Bob Howel''s ADV if he ever answers my e-mail order that is!
Who was telling me the Aussie Sea Hornet din valves will work on OMS cylinders without any Inspiration fairing flexing or modification? I don't want any local boats to freak trying to fill factory AP tanks.
at 10 feet if you had a perfect flushed loop you could just get to 1.3!! 10ft/3 meters=1.3 atm, 1.3atm * 100% =1.3 PO2 @ 20ft/6M its possible to get to a 1.3 without flushing all the nitrogen out because you are at 1.6 ata.
Use .7 for decent when you get to the bottom switch to a 1.3.
You have 3 hours at a 1.3 exposure..
It is important you raise your setpoint by the time you reach 77 feet (or at least keep the PO2 above this).
at 77 feet you have the same po2 as an air diver.. if you go deeper, your PO2 is lower than that of an Open circuit diver and your nitrogen loading is higher.. The idea is to reduce your loading not increase it.. If you want to be overly cautious use a set point of 1.0 - 1.2.
On deep air dives (which I only do if its the only option, with a setpoint of 1.3 @171 ft you are the same Po2 and nitrogen as an Open circuit diver Air diver, below this you have a higher nitrogen loading since the PO2 will remain at 1.3(and the OC divers will be climbing), Rusty should have gone over these concepts, are you sure you didn't mis-understand him??
I have used the inspiration on air to 220+ft and 300 on trimix.
the NOAA limits for a 1.3 is 3 hours single exposure(its no coincidence the inspiration is rated as a 3 hour scrubber) 3.5 hours 24 hour limit.. When I go away on trips it not uncommon for me to run 5 hours- 6 hours a day in the water for a week or more, definately over NOAA limits, but I make sure I ALWAYS have at least a 90 min surface interval so at worst case my CNS% is 50% upon entering water.. I only exceed single exposure limits on extreme deep and long dives where I'll have an extended time doing Deco at a 1.6.
Use .7 for decent when you get to the bottom switch to a 1.3.
You have 3 hours at a 1.3 exposure..
It is important you raise your setpoint by the time you reach 77 feet (or at least keep the PO2 above this).
at 77 feet you have the same po2 as an air diver.. if you go deeper, your PO2 is lower than that of an Open circuit diver and your nitrogen loading is higher.. The idea is to reduce your loading not increase it.. If you want to be overly cautious use a set point of 1.0 - 1.2.
On deep air dives (which I only do if its the only option, with a setpoint of 1.3 @171 ft you are the same Po2 and nitrogen as an Open circuit diver Air diver, below this you have a higher nitrogen loading since the PO2 will remain at 1.3(and the OC divers will be climbing), Rusty should have gone over these concepts, are you sure you didn't mis-understand him??
I have used the inspiration on air to 220+ft and 300 on trimix.
the NOAA limits for a 1.3 is 3 hours single exposure(its no coincidence the inspiration is rated as a 3 hour scrubber) 3.5 hours 24 hour limit.. When I go away on trips it not uncommon for me to run 5 hours- 6 hours a day in the water for a week or more, definately over NOAA limits, but I make sure I ALWAYS have at least a 90 min surface interval so at worst case my CNS% is 50% upon entering water.. I only exceed single exposure limits on extreme deep and long dives where I'll have an extended time doing Deco at a 1.6.
Whats really worrying is that someone could complete their Inspiration training and not understand this. Its pretty basic stuff and understanding O2 Partial Pressures is key to the whole usage of any rebreather
DrySuitDave I would really suggest you call your instructor and get him to make sure you understand O2 Partial pressures and why its very obvious that the Inspiration will keep injecting O2 the whole time if you use a 1.3 setpoint shallower than 10Ft (its SUPPOSED to do this), its just that YOURE not supposed to be using a 1.3 setpoint shallower than 10ft
It is also very important that you understand the CNS clock. yes its a 3 hour single exposure and 3.5 hours in 24, BUT that total daily exposure rapidly declines if you are doing multiday daiving down to about 1.5 hours a day over a week or so
If you are using air as a diluent and comparing the PPN2 (nitrogen) then 45m is the magic depth. At this point the Nitrogen PPO2 in the loop (at 1.3 setpoint) equals what it would be diving on OC air. Deeper than this the inspirations runs a higher PPN2 and shallower a lower PPN2. Its all to do with Constant partial Pressure v Constant percentage.
Many believe that O2 is more narcotic than nitrogen (its more lipid soluble) and that on a rebreather with raised O2 PP's you get narced shallower than on OC (thats certainly is what I notice, at around the 44m mark on the turtle I feel about the same as 50m on air)
I think my weekend project (when I get back from the Moldavia) will be to add a Partial Pressures and Setpoint explanation section to my site Diver Mole, Your Inspiration Buddy
Next week I'm doing my Normoxic Trimix with Dave Thompson so that should be fun and clear my head on those 50m dives
DrySuitDave I would really suggest you call your instructor and get him to make sure you understand O2 Partial pressures and why its very obvious that the Inspiration will keep injecting O2 the whole time if you use a 1.3 setpoint shallower than 10Ft (its SUPPOSED to do this), its just that YOURE not supposed to be using a 1.3 setpoint shallower than 10ft
It is also very important that you understand the CNS clock. yes its a 3 hour single exposure and 3.5 hours in 24, BUT that total daily exposure rapidly declines if you are doing multiday daiving down to about 1.5 hours a day over a week or so
If you are using air as a diluent and comparing the PPN2 (nitrogen) then 45m is the magic depth. At this point the Nitrogen PPO2 in the loop (at 1.3 setpoint) equals what it would be diving on OC air. Deeper than this the inspirations runs a higher PPN2 and shallower a lower PPN2. Its all to do with Constant partial Pressure v Constant percentage.
Many believe that O2 is more narcotic than nitrogen (its more lipid soluble) and that on a rebreather with raised O2 PP's you get narced shallower than on OC (thats certainly is what I notice, at around the 44m mark on the turtle I feel about the same as 50m on air)
I think my weekend project (when I get back from the Moldavia) will be to add a Partial Pressures and Setpoint explanation section to my site Diver Mole, Your Inspiration Buddy
Next week I'm doing my Normoxic Trimix with Dave Thompson so that should be fun and clear my head on those 50m dives
dave once bubbled
"Who was telling me the Aussie Sea Hornet din valves will work on OMS cylinders without any Inspiration fairing flexing or modification? I don't want any local boats to freak trying to fill factory AP tanks."
I did.. the only thing you have to do is slightly enlarge the valve opening.. a minute or two with a dremmel tool solves this.. the valve with the tank is about 1/4 inch too long, otherwise everything fits perfectly..
"Who was telling me the Aussie Sea Hornet din valves will work on OMS cylinders without any Inspiration fairing flexing or modification? I don't want any local boats to freak trying to fill factory AP tanks."
I did.. the only thing you have to do is slightly enlarge the valve opening.. a minute or two with a dremmel tool solves this.. the valve with the tank is about 1/4 inch too long, otherwise everything fits perfectly..
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