Onboard vs. Offboard Deco

Steve · 3rd November 2006, 01:54

Quote: (Originally Posted by PaulTG2)

What are people's thoughts on onboard vs offboard decompression.

If the number of posts on this site dedicated to the problems with the 2 most common onboard setpoint controllers that do deco calculations are anything to go by then I will continue to stay away from them. I take my diving and life more seriously than to use them.

If there is a difference between onbaord and offboard deco then there is a problem somewhere. It is as simple as that. It is most likely to be with the aforementioned bug riddled HH or Vision or poor diving practices. Why plan a SCR bailout around the most likely thing to stuff up on a rebreather?

It seems there is way to many people keen to buy more gear to make up for their lack of ability and shitty gear. It's a bitter pill but a good many people need to swallow it

silent running · 3rd November 2006, 03:17

Quote: (Originally Posted by Mark Chase)

It depends on how you rate the benefits.

On pure deco time a 150min run time dive to 70 ish there would be about 15mins between the on board P02 monitoring VR3 and the of board set at 1.25. No big deal. However the other thing was the VR3 could provide deco info in the event of going semi closed and it could provide a PP02 confirmation if i were reduced to diving the HUD and the VR3 to get home. These benefits appealed to me. The integrated VR3 also acted as back up to the non integrated VR3 if I had to bail out to OX.

Its and expensive way to be free of tables but I hated tables.

ATB

Mark Chase

Hi Mark, I'm assuming the reason for the difference btw the deco times on the HH and VR is because of the different algs, right? I would rather just stick with one, as I would find it annoying having to wait for both to clear, especially if something came up and I had to get out of the water before the longer one cleared and I bent it.

I understand the safety factor idea of the 4th cell in an SCR situation, but IMHO, it's not going to provide that much, not if you just err on the conservative side when deciding on your average mix for SCR BO on a stand alone comp. Having dived a lot of SCR before moving over to CCR, I tried the both the averaging approach and the Oxy2 integrated O2 loop monitor on the Drager. If I picked the right mix, the difference was just a few minutes on square profile deco dives, which is what you'd be doing in an emergency. Not enough IMHO, to justify a whole other set of seals, clutter, calibrations and another O2 sensor that has to be replaced. Never mind the inconvenient deco alg incompatibility with your onboard or the fact that, god willing you will hopefully never have to go SCR on your CCR.

What's so bad about tables? You can laminate them and stick them in your pocket with a bottom timer and forget about them. BTs seem very reliable for all but the most extreme diving and tables never flood or have to be sent back to the manufacturer, who might live in another country...

silent running · 3rd November 2006, 07:20

Quote: (Originally Posted by Steve)

If the number of posts on this site dedicated to the problems with the 2 most common onboard setpoint controllers that do deco calculations are anything to go by then I will continue to stay away from them. I take my diving and life more seriously than to use them.

If there is a difference between onbaord and offboard deco then there is a problem somewhere. It is as simple as that. It is most likely to be with the aforementioned bug riddled HH or Vision or poor diving practices. Why plan a SCR bailout around the most likely thing to stuff up on a rebreather?

It seems there is way to many people keen to buy more gear to make up for their lack of ability and shitty gear. It's a bitter pill but a good many people need to swallow it

Steve has said a mouthful, and I agree. Here comes my mouthful. Novice divers who are intimidated by the many responsibilities of CCR diving will find comfort in the idea of integrated deco with the promise of "It's all taken care of", not the kind of comfort I like when diving CCR.

The fact is that a CCR problem has never really been taken care of until you take care of it yourself. Constant PO2 diving is deceptively simple-as long as you can maintain a constant PO2, your dive plan is pretty simple. The problems start when you can't maintain a constant PO2, either due to equipment failure, or human failure-not paying attention, bad planning, not enough gas.

No matter which failure you have, decisions will have to be made, decisions which current integrated ECCR controllers are not sophisticated/thorough enough to make without human oversight. I want to be able to see my PO2 even with an electronics/main power failure. And I want to be able to disable the solenoid in a low power/emergency situation so I can keep the displays going and better manage my emergency-2 examples. Anyone can manage the PO2 well enough as long as they have a reliable display, I don't need any help beyond that. The best controller is one which controls the least, yet is able to maintain PO2 best-IMHO.

Help is the key word. Most CCR divers go on and on about complacency and it's insidious effects, but many still find integrated deco an attractive proposition. I'm not sure I understand this. The truth is that CCR diving always requires a high level of diver involvement in the system. The optimal level is debatable, but one thing is sure, you need maximum flexability to handle the many complexities of constant PO2 diving emergencies. I can think of no other land mammals able maintain constant PO2 through any means, mechanical or otherwise.

Oh and finally, there's the division of labor. It's plenty hard to design an ECCR that has a good scrubber, low WOB, maintains set point well and is reliable. Asking for an integrated deco function with all that is, IMHO, expecting a lot. I say let the CCR designers do their best and let the dive comp manufacurers do their best and let us divers do our best. It's not so reasuring, but it is realistic.

Mark Chase · 3rd November 2006, 09:09

[quote]

Quote: (Originally Posted by silent running)

Hi Mark, I'm assuming the reason for the difference btw the deco times on the HH and VR is because of the different algs, right?

No, this was two VR3s one plumbed in and one stand alone running 1.25set point.

Quote:

I would rather just stick with one, as I would find it annoying having to wait for both to clear, especially if something came up and I had to get out of the water before the longer one cleared and I bent it.

As I said its mildly irritating but I just accept the padding or I bend the stand alone VR3. It doesn't mind and lets me dive again even the same day.

Quote:

I understand the safety factor idea of the 4th cell in an SCR situation, but IMHO, it's not going to provide that much, not if you just err on the conservative side when deciding on your average mix for SCR BO on a stand alone comp.

Erring on the side of caution after something thats forced you to bail out to SC is not always an option. I hate going SC and when I tried an entire 120min deco on SC (to see if i could) I had a god awfull headache after the dive and a very sore nose.

Any dive that forced me to go SC rather than bailout OC will be a high stress situation. Being able to focus on running the unit and just relying on the VR3 /Sherewater what ever to sort out the deco and tell me the ASAP time out of the water will (for me) greatly reduce the stress.

Quote:

Having dived a lot of SCR before moving over to CCR, I tried the both the averaging approach and the Oxy2 integrated O2 loop monitor on the Drager. If I picked the right mix, the difference was just a few minutes on square profile deco dives, which is what you'd be doing in an emergency. Not enough IMHO, to justify a whole other set of seals, clutter, calibrations and another O2 sensor that has to be replaced. Never mind the inconvenient deco alg incompatibility with your onboard or the fact that, god willing you will hopefully never have to go SCR on your CCR.

Discuss the situation for me. Your stuck inside a wreck at 65m you have been there for an hour, you just got out but your scrubber is screwed because its the second dive on it and you don't trust it to last the 4 hours of deco, you haven't got enough bailout to go OC so you go semi closed.

Plan the deco for me 15/65 inboard, 18/45 off board 50% off board

What's so bad about tables? You can laminate them and stick them in your pocket with a bottom timer and forget about them

I don't and never have carried tables to cover me in the above situation. A wreck penetration in low (less then 10m) viz in silty conditions in a changeable sea is a typical dive for me. Back when i used to use tables it would have been irrelevant because id be dead. Now survival is an option I need to plan for it.

Quote:

. BTs seem very reliable for all but the most extreme diving and tables never flood or have to be sent back to the manufacturer, who might live in another country...

Really? do you think so?

Hers the print out from my bottom timer on a 102m dive

Hears the print out from my back up computer

The computer appeared to be working perfectly but it showed my depth as 116m. I cross referenced with my back up computer and my primary VR3 which both agreed i was at 102. I followed the VR3 out. If i only had two bottom timers and depth gauges i wonder which one i would have trusted at the 66m gas switch.

ATB

Mark Chase

Mark Chase · 3rd November 2006, 09:22

Quote: (Originally Posted by silent running)

Steve has said a mouthful, and I agree. Here comes my mouthful. Novice divers who are intimidated by the many responsibilities of CCR diving will find comfort in the idea of integrated deco with the promise of "It's all taken care of", not the kind of comfort I like when diving CCR.

The fact is that a CCR problem has never really been taken care of until you take care of it yourself. Constant PO2 diving is deceptively simple-as long as you can maintain a constant PO2, your dive plan is pretty simple. The problems start when you can't maintain a constant PO2, either due to equipment failure, or human failure-not paying attention, bad planning, not enough gas.

No matter which failure you have, decisions will have to be made, decisions which current integrated ECCR controllers are not sophisticated/thorough enough to make without human oversight. I want to be able to see my PO2 even with an electronics/main power failure. And I want to be able to disable the solenoid in a low power/emergency situation so I can keep the displays going and better manage my emergency-2 examples. Anyone can manage the PO2 well enough as long as they have a reliable display, I don't need any help beyond that. The best controller is one which controls the least, yet is able to maintain PO2 best-IMHO.

Help is the key word. Most CCR divers go on and on about complacency and it's insidious effects, but many still find integrated deco an attractive proposition. I'm not sure I understand this. The truth is that CCR diving always requires a high level of diver involvement in the system. The optimal level is debatable, but one thing is sure, you need maximum flexability to handle the many complexities of constant PO2 diving emergencies. I can think of no other land mammals able maintain constant PO2 through any means, mechanical or otherwise.

Oh and finally, there's the division of labor. It's plenty hard to design an ECCR that has a good scrubber, low WOB, maintains set point well and is reliable. Asking for an integrated deco function with all that is, IMHO, expecting a lot. I say let the CCR designers do their best and let the dive comp manufacurers do their best and let us divers do our best. It's not so reasuring, but it is realistic.

Quite obviously we look at this from completely different perspectives.

I had a classic with no on board deco. I plumbed in a VR3 and I ran an isolated VR3 as back up. I also ran a completely independent HUD that could indicate set point within 0.1. In my pocket i had a bottom timer and depth gage. (Suunto Vytec in Gage mode)

TO become blind on the CCR i would have to have had a total failure of two hand sets one VR3 and one HUD. All on the same dive.

This would (IMHO) ony result from a totally flooded unit in which case running the unit the unit is no a consideration any more. God forbid you could recover the loop and the WOB of the solid lump of sofnalime is allowing you to go semi closed then i could switch the set point on the stand alone VR3 to 1.0and deco out on that.

If all this lot decides to fail same dive I still have a bottom timer and DOTF left to play with but I will be expecting the wreck to collapse on me any second or to be hit by a submarine whilst on deco.

ATB

Mark Chase
The classic provides to seporate PP02 readouts

silent running · 3rd November 2006, 11:28

[quote=Mark Chase;76183]

Quote:

No, this was two VR3s one plumbed in and one stand alone running 1.25set point.

Sorry Mark, I didn't realize you were talking about 2 VRs. If one is off from the other by 15 minutes, the SP controller is not very good at doing it's job.

[quote=Mark Chase;76183][quote]Erring on the side of caution after something thats forced you to bail out to SC is not always an option. I hate going SC and when I tried an entire 120min deco on SC (to see if i could) I had a god awfull headache after the dive and a very sore nose. Any dive that forced me to go SC rather than bailout OC will be a high stress situation. Being able to focus on running the unit and just relying on the VR3 /Sherewater what ever to sort out the deco and tell me the ASAP time out of the water will (for me) greatly reduce the stress.[quote]

Yes, I understand it will be a high stress situation. But if you have your conservative SCR inspired gas average in the OC gas list of your VR/HE, other than gas limits, why would it be so hard to manage? You switch to that OC gas on the comp and wait for the update. Sure it will be a shock when you see your TTS, but SCR should give you a lot of time, you will have to hope it's enough at a 4/1 ratio. Having an inline sensor will allow you to determine the exact time, but either way you only have so much gas and you will either get out of the water in good health or not. If I was using the averaging SCR OC gas mix, I would probably breathe down the entire cyl, even if my comp told me I was done.

[quote=Mark Chase;76183][quote]Discuss the situation for me. Your stuck inside a wreck at 65m you have been there for an hour, you just got out but your scrubber is screwed because its the second dive on it and you don't trust it to last the 4 hours of deco, you haven't got enough bailout to go OC so you go semi closed.

Plan the deco for me 15/65 inboard, 18/45 off board 50% off board.[quote]

What was your SP? How much inboard dil do you have left after descent? How big is the inboard cyl?

[quote=Mark Chase;76183][quote]I don't and never have carried tables to cover me in the above situation. A wreck penetration in low (less then 10m) viz in silty conditions in a changeable sea is a typical dive for me. Back when i used to use tables it would have been irrelevant because id be dead. Now survival is an option I need to plan for it.

Quote:

I carry PO2 tables for my off board comp dying and OC tables for the OC BO gas I'm carrying, not for the SCR average inspired gas. I guess I could carry those too, in case of comp failure and over stay.

What's so bad about tables? You can laminate them and stick them in your pocket with a bottom timer and forget about them

Really? do you think so?

Hers the print out from my bottom timer on a 102m dive

Hears the print out from my back up computer

The computer appeared to be working perfectly but it showed my depth as 116m. I cross referenced with my back up computer and my primary VR3 which both agreed i was at 102. I followed the VR3 out. If i only had two bottom timers and depth gauges i wonder which one i would have trusted at the 66m gas switch.

ATB

Mark Chase

Uwatec BTs are cal'd for freshwater, maybe other BTs are too, which could explain the deeper depth reading, and which would only get worse the deeper you go. Otherwise, I've not heard of any BTs screwing up major. If your first switch is at 66M and it's a fresh water cal'd unit, the difference will be much less from the MSW reading on a PO2 comp and maybe not such a big deal. -Andy

Mark Chase · 3rd November 2006, 12:33

Quote: (Originally Posted by silent running)

Uwatec BTs are cal'd for freshwater, maybe other BTs are too, which could explain the deeper depth reading, and which would only get worse the deeper you go. Otherwise, I've not heard of any BTs screwing up major. If your first switch is at 66M and it's a fresh water cal'd unit, the difference will be much less from the MSW reading on a PO2 comp and maybe not such a big deal. -Andy

As you can see from the printouts ther units were Suunto's Top one was my Vytec and the bottom one was my Vyper.

Both are calibrated for sea water but even if they wernt it wouldent explain the 14m diferance in the two printouts. The error was still present in the shalows. Look at the 6m stop depth, its saying I was at 20m.

The Vytec depth sensor had failed and was replaced under warrentee.

ATB

Mark Chase

silent running · 3rd November 2006, 20:09

Quote: (Originally Posted by Mark Chase)

As you can see from the printouts ther units were Suunto's Top one was my Vytec and the bottom one was my Vyper.

Both are calibrated for sea water but even if they wernt it wouldent explain the 14m diferance in the two printouts. The error was still present in the shalows. Look at the 6m stop depth, its saying I was at 20m.

The Vytec depth sensor had failed and was replaced under warrentee.

ATB

Mark Chase

Hi Mark, now I see. I was fading at the end of that last post as you can see from the botched multiquote, and then went to bed.

So the Suunto depth sensor died? Is this a common problem? I thought they were supposed to be decent quality. I have an Uwatec, which hasn't given me any trouble other than blanking the depth deeper than 100M. It came back as soon as I ascended above 100M. I don't know anybody who has anything else, and everybody seems to think they're reliable to 100M, so I have no reason not to trust mine. But if I were doing big dives on a regular basis, I would probably have a back up comp as well the BT.

It also occured to me after reading the posts again, that you regularly dive in overhead environments in the 70+M range and I don't. But again, if I did, I would bring another stand alone comp.

But back to the issue of an inline sensor or not, the 15 minute deco discrepancy on a big dive is something I would sweat, it's important. Can you clarify which VR was inline, the short deco time or the longer? Thanks, -Andy

Mark Chase · 4th November 2006, 07:24

Quote: (Originally Posted by silent running)

Hi Mark, now I see. I was fading at the end of that last post as you can see from the botched multiquote, and then went to bed.

So the Suunto depth sensor died? Is this a common problem? I thought they were supposed to be decent quality. I have an Uwatec, which hasn't given me any trouble other than blanking the depth deeper than 100M. It came back as soon as I ascended above 100M. I don't know anybody who has anything else, and everybody seems to think they're reliable to 100M, so I have no reason not to trust mine. But if I were doing big dives on a regular basis, I would probably have a back up comp as well the BT.

It also occured to me after reading the posts again, that you regularly dive in overhead environments in the 70+M range and I don't. But again, if I did, I would bring another stand alone comp.

But back to the issue of an inline sensor or not, the 15 minute deco discrepancy on a big dive is something I would sweat, it's important. Can you clarify which VR was inline, the short deco time or the longer? Thanks, -Andy

The depth sensors on all dive computers are a week link. They are cheep low quality items in the world of pressure sensors and they are easily damaged by dropping the computer. Having dived with three dive computers and seen three different depth readings displayed I don't think they are particularly accurate even when they do work.

I don't know of any specific issue with the Suunto but i have herd many tails of dodgy depth sensors generaly.

In line VR3 always ran shorter than the stand alone unit. Usually between 5 -15mins. Both VR3s were capable of PP02 monitoring and i would swap their duties around occasionally jut to make sure they both worked OK and the discrepancy remained. It didn't bother me over the period of 80mins+ deco. Id usually sit out the extra time and surface as soon as it cleared where as before i had an integrated I would clear the VR3 then add on a bit just in case so i was probably doing 10mins extra on top of that again.

Clearing deco a few min quicker using it in line is very low down on my list of priorities. I am much more interested in its role as an independent back up PP02 monitor and for calculation of deco following a problem. I have never been in a hurry to get out of the water unless staying in has been bad for my health.

ATB

Mark CHase

denzel · 4th November 2006, 08:59

Offboard.
KISS.

Q's?

Denz.

PS Mark, is there any piece of equipment that doesn't break in your hands?

3rd November 2006, 01:54	#11 (permalink)
Steve Ladies bring a plate Current Rebreather/s: Megalodon Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Classic Kiss MK 15.X Home Build Join Date: Feb 2005 Location: Perth - Australia Posts: 1,126	Re: Onboard vs. Offboard Deco Quote: (Originally Posted by PaulTG2) What are people's thoughts on onboard vs offboard decompression. If the number of posts on this site dedicated to the problems with the 2 most common onboard setpoint controllers that do deco calculations are anything to go by then I will continue to stay away from them. I take my diving and life more seriously than to use them. If there is a difference between onbaord and offboard deco then there is a problem somewhere. It is as simple as that. It is most likely to be with the aforementioned bug riddled HH or Vision or poor diving practices. Why plan a SCR bailout around the most likely thing to stuff up on a rebreather? It seems there is way to many people keen to buy more gear to make up for their lack of ability and shitty gear. It's a bitter pill but a good many people need to swallow it __________________ WARNING: I contain occasional coarse language, extreme sexual references, nudity, and adult themes, which may offend some people - Usually churchy types. Last edited by Steve : 3rd November 2006 at 01:56.
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3rd November 2006, 03:17	#12 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,873	Re: Onboard vs. Offboard Deco Quote: (Originally Posted by Mark Chase) It depends on how you rate the benefits. On pure deco time a 150min run time dive to 70 ish there would be about 15mins between the on board P02 monitoring VR3 and the of board set at 1.25. No big deal. However the other thing was the VR3 could provide deco info in the event of going semi closed and it could provide a PP02 confirmation if i were reduced to diving the HUD and the VR3 to get home. These benefits appealed to me. The integrated VR3 also acted as back up to the non integrated VR3 if I had to bail out to OX. Its and expensive way to be free of tables but I hated tables. ATB Mark Chase Hi Mark, I'm assuming the reason for the difference btw the deco times on the HH and VR is because of the different algs, right? I would rather just stick with one, as I would find it annoying having to wait for both to clear, especially if something came up and I had to get out of the water before the longer one cleared and I bent it. I understand the safety factor idea of the 4th cell in an SCR situation, but IMHO, it's not going to provide that much, not if you just err on the conservative side when deciding on your average mix for SCR BO on a stand alone comp. Having dived a lot of SCR before moving over to CCR, I tried the both the averaging approach and the Oxy2 integrated O2 loop monitor on the Drager. If I picked the right mix, the difference was just a few minutes on square profile deco dives, which is what you'd be doing in an emergency. Not enough IMHO, to justify a whole other set of seals, clutter, calibrations and another O2 sensor that has to be replaced. Never mind the inconvenient deco alg incompatibility with your onboard or the fact that, god willing you will hopefully never have to go SCR on your CCR. What's so bad about tables? You can laminate them and stick them in your pocket with a bottom timer and forget about them. BTs seem very reliable for all but the most extreme diving and tables never flood or have to be sent back to the manufacturer, who might live in another country... Last edited by silent running : 3rd November 2006 at 03:19.
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3rd November 2006, 07:20	#13 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,873	Re: Onboard vs. Offboard Deco Quote: (Originally Posted by Steve) If the number of posts on this site dedicated to the problems with the 2 most common onboard setpoint controllers that do deco calculations are anything to go by then I will continue to stay away from them. I take my diving and life more seriously than to use them. If there is a difference between onbaord and offboard deco then there is a problem somewhere. It is as simple as that. It is most likely to be with the aforementioned bug riddled HH or Vision or poor diving practices. Why plan a SCR bailout around the most likely thing to stuff up on a rebreather? It seems there is way to many people keen to buy more gear to make up for their lack of ability and shitty gear. It's a bitter pill but a good many people need to swallow it Steve has said a mouthful, and I agree. Here comes my mouthful. Novice divers who are intimidated by the many responsibilities of CCR diving will find comfort in the idea of integrated deco with the promise of "It's all taken care of", not the kind of comfort I like when diving CCR. The fact is that a CCR problem has never really been taken care of until you take care of it yourself. Constant PO2 diving is deceptively simple-as long as you can maintain a constant PO2, your dive plan is pretty simple. The problems start when you can't maintain a constant PO2, either due to equipment failure, or human failure-not paying attention, bad planning, not enough gas. No matter which failure you have, decisions will have to be made, decisions which current integrated ECCR controllers are not sophisticated/thorough enough to make without human oversight. I want to be able to see my PO2 even with an electronics/main power failure. And I want to be able to disable the solenoid in a low power/emergency situation so I can keep the displays going and better manage my emergency-2 examples. Anyone can manage the PO2 well enough as long as they have a reliable display, I don't need any help beyond that. The best controller is one which controls the least, yet is able to maintain PO2 best-IMHO. Help is the key word. Most CCR divers go on and on about complacency and it's insidious effects, but many still find integrated deco an attractive proposition. I'm not sure I understand this. The truth is that CCR diving always requires a high level of diver involvement in the system. The optimal level is debatable, but one thing is sure, you need maximum flexability to handle the many complexities of constant PO2 diving emergencies. I can think of no other land mammals able maintain constant PO2 through any means, mechanical or otherwise. Oh and finally, there's the division of labor. It's plenty hard to design an ECCR that has a good scrubber, low WOB, maintains set point well and is reliable. Asking for an integrated deco function with all that is, IMHO, expecting a lot. I say let the CCR designers do their best and let the dive comp manufacurers do their best and let us divers do our best. It's not so reasuring, but it is realistic. Last edited by silent running : 3rd November 2006 at 07:40.
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3rd November 2006, 09:09	#14 (permalink)
Mark Chase RBW Member Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Jan 2005 Location: Kent Posts: 2,858	Re: Onboard vs. Offboard Deco [quote] Quote: (Originally Posted by silent running) Hi Mark, I'm assuming the reason for the difference btw the deco times on the HH and VR is because of the different algs, right? No, this was two VR3s one plumbed in and one stand alone running 1.25set point. Quote: I would rather just stick with one, as I would find it annoying having to wait for both to clear, especially if something came up and I had to get out of the water before the longer one cleared and I bent it. As I said its mildly irritating but I just accept the padding or I bend the stand alone VR3. It doesn't mind and lets me dive again even the same day. Quote: I understand the safety factor idea of the 4th cell in an SCR situation, but IMHO, it's not going to provide that much, not if you just err on the conservative side when deciding on your average mix for SCR BO on a stand alone comp. Erring on the side of caution after something thats forced you to bail out to SC is not always an option. I hate going SC and when I tried an entire 120min deco on SC (to see if i could) I had a god awfull headache after the dive and a very sore nose. Any dive that forced me to go SC rather than bailout OC will be a high stress situation. Being able to focus on running the unit and just relying on the VR3 /Sherewater what ever to sort out the deco and tell me the ASAP time out of the water will (for me) greatly reduce the stress. Quote: Having dived a lot of SCR before moving over to CCR, I tried the both the averaging approach and the Oxy2 integrated O2 loop monitor on the Drager. If I picked the right mix, the difference was just a few minutes on square profile deco dives, which is what you'd be doing in an emergency. Not enough IMHO, to justify a whole other set of seals, clutter, calibrations and another O2 sensor that has to be replaced. Never mind the inconvenient deco alg incompatibility with your onboard or the fact that, god willing you will hopefully never have to go SCR on your CCR. Discuss the situation for me. Your stuck inside a wreck at 65m you have been there for an hour, you just got out but your scrubber is screwed because its the second dive on it and you don't trust it to last the 4 hours of deco, you haven't got enough bailout to go OC so you go semi closed. Plan the deco for me 15/65 inboard, 18/45 off board 50% off board What's so bad about tables? You can laminate them and stick them in your pocket with a bottom timer and forget about them I don't and never have carried tables to cover me in the above situation. A wreck penetration in low (less then 10m) viz in silty conditions in a changeable sea is a typical dive for me. Back when i used to use tables it would have been irrelevant because id be dead. Now survival is an option I need to plan for it. Quote: . BTs seem very reliable for all but the most extreme diving and tables never flood or have to be sent back to the manufacturer, who might live in another country... Really? do you think so? Hers the print out from my bottom timer on a 102m dive Hears the print out from my back up computer The computer appeared to be working perfectly but it showed my depth as 116m. I cross referenced with my back up computer and my primary VR3 which both agreed i was at 102. I followed the VR3 out. If i only had two bottom timers and depth gauges i wonder which one i would have trusted at the 66m gas switch. ATB Mark Chase __________________ See my "Doing It Chasey" video where I'm locked into a padded room, naked, with two ball bearings and within an Hour, I manage to lose one and break the other!!! Kevin Juergensen 16/11/08 [/quote]
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3rd November 2006, 09:22	#15 (permalink)
Mark Chase RBW Member Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Jan 2005 Location: Kent Posts: 2,858	Re: Onboard vs. Offboard Deco Quote: (Originally Posted by silent running) Steve has said a mouthful, and I agree. Here comes my mouthful. Novice divers who are intimidated by the many responsibilities of CCR diving will find comfort in the idea of integrated deco with the promise of "It's all taken care of", not the kind of comfort I like when diving CCR. The fact is that a CCR problem has never really been taken care of until you take care of it yourself. Constant PO2 diving is deceptively simple-as long as you can maintain a constant PO2, your dive plan is pretty simple. The problems start when you can't maintain a constant PO2, either due to equipment failure, or human failure-not paying attention, bad planning, not enough gas. No matter which failure you have, decisions will have to be made, decisions which current integrated ECCR controllers are not sophisticated/thorough enough to make without human oversight. I want to be able to see my PO2 even with an electronics/main power failure. And I want to be able to disable the solenoid in a low power/emergency situation so I can keep the displays going and better manage my emergency-2 examples. Anyone can manage the PO2 well enough as long as they have a reliable display, I don't need any help beyond that. The best controller is one which controls the least, yet is able to maintain PO2 best-IMHO. Help is the key word. Most CCR divers go on and on about complacency and it's insidious effects, but many still find integrated deco an attractive proposition. I'm not sure I understand this. The truth is that CCR diving always requires a high level of diver involvement in the system. The optimal level is debatable, but one thing is sure, you need maximum flexability to handle the many complexities of constant PO2 diving emergencies. I can think of no other land mammals able maintain constant PO2 through any means, mechanical or otherwise. Oh and finally, there's the division of labor. It's plenty hard to design an ECCR that has a good scrubber, low WOB, maintains set point well and is reliable. Asking for an integrated deco function with all that is, IMHO, expecting a lot. I say let the CCR designers do their best and let the dive comp manufacurers do their best and let us divers do our best. It's not so reasuring, but it is realistic. Quite obviously we look at this from completely different perspectives. I had a classic with no on board deco. I plumbed in a VR3 and I ran an isolated VR3 as back up. I also ran a completely independent HUD that could indicate set point within 0.1. In my pocket i had a bottom timer and depth gage. (Suunto Vytec in Gage mode) TO become blind on the CCR i would have to have had a total failure of two hand sets one VR3 and one HUD. All on the same dive. This would (IMHO) ony result from a totally flooded unit in which case running the unit the unit is no a consideration any more. God forbid you could recover the loop and the WOB of the solid lump of sofnalime is allowing you to go semi closed then i could switch the set point on the stand alone VR3 to 1.0and deco out on that. If all this lot decides to fail same dive I still have a bottom timer and DOTF left to play with but I will be expecting the wreck to collapse on me any second or to be hit by a submarine whilst on deco. ATB Mark Chase The classic provides to seporate PP02 readouts __________________ See my "Doing It Chasey" video where I'm locked into a padded room, naked, with two ball bearings and within an Hour, I manage to lose one and break the other!!! Kevin Juergensen 16/11/08 [/quote]
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3rd November 2006, 11:28	#16 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,873	Re: Onboard vs. Offboard Deco [quote=Mark Chase;76183] Quote: No, this was two VR3s one plumbed in and one stand alone running 1.25set point. Sorry Mark, I didn't realize you were talking about 2 VRs. If one is off from the other by 15 minutes, the SP controller is not very good at doing it's job. [quote=Mark Chase;76183][quote]Erring on the side of caution after something thats forced you to bail out to SC is not always an option. I hate going SC and when I tried an entire 120min deco on SC (to see if i could) I had a god awfull headache after the dive and a very sore nose. Any dive that forced me to go SC rather than bailout OC will be a high stress situation. Being able to focus on running the unit and just relying on the VR3 /Sherewater what ever to sort out the deco and tell me the ASAP time out of the water will (for me) greatly reduce the stress.[quote] Yes, I understand it will be a high stress situation. But if you have your conservative SCR inspired gas average in the OC gas list of your VR/HE, other than gas limits, why would it be so hard to manage? You switch to that OC gas on the comp and wait for the update. Sure it will be a shock when you see your TTS, but SCR should give you a lot of time, you will have to hope it's enough at a 4/1 ratio. Having an inline sensor will allow you to determine the exact time, but either way you only have so much gas and you will either get out of the water in good health or not. If I was using the averaging SCR OC gas mix, I would probably breathe down the entire cyl, even if my comp told me I was done. [quote=Mark Chase;76183][quote]Discuss the situation for me. Your stuck inside a wreck at 65m you have been there for an hour, you just got out but your scrubber is screwed because its the second dive on it and you don't trust it to last the 4 hours of deco, you haven't got enough bailout to go OC so you go semi closed. Plan the deco for me 15/65 inboard, 18/45 off board 50% off board.[quote] What was your SP? How much inboard dil do you have left after descent? How big is the inboard cyl? [quote=Mark Chase;76183][quote]I don't and never have carried tables to cover me in the above situation. A wreck penetration in low (less then 10m) viz in silty conditions in a changeable sea is a typical dive for me. Back when i used to use tables it would have been irrelevant because id be dead. Now survival is an option I need to plan for it. Quote: I carry PO2 tables for my off board comp dying and OC tables for the OC BO gas I'm carrying, not for the SCR average inspired gas. I guess I could carry those too, in case of comp failure and over stay. What's so bad about tables? You can laminate them and stick them in your pocket with a bottom timer and forget about them Really? do you think so? Hers the print out from my bottom timer on a 102m dive Hears the print out from my back up computer The computer appeared to be working perfectly but it showed my depth as 116m. I cross referenced with my back up computer and my primary VR3 which both agreed i was at 102. I followed the VR3 out. If i only had two bottom timers and depth gauges i wonder which one i would have trusted at the 66m gas switch. ATB Mark Chase Uwatec BTs are cal'd for freshwater, maybe other BTs are too, which could explain the deeper depth reading, and which would only get worse the deeper you go. Otherwise, I've not heard of any BTs screwing up major. If your first switch is at 66M and it's a fresh water cal'd unit, the difference will be much less from the MSW reading on a PO2 comp and maybe not such a big deal. -Andy Last edited by silent running : 3rd November 2006 at 12:00.
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3rd November 2006, 12:33	#17 (permalink)
Mark Chase RBW Member Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Jan 2005 Location: Kent Posts: 2,858	Re: Onboard vs. Offboard Deco Quote: (Originally Posted by silent running) Uwatec BTs are cal'd for freshwater, maybe other BTs are too, which could explain the deeper depth reading, and which would only get worse the deeper you go. Otherwise, I've not heard of any BTs screwing up major. If your first switch is at 66M and it's a fresh water cal'd unit, the difference will be much less from the MSW reading on a PO2 comp and maybe not such a big deal. -Andy As you can see from the printouts ther units were Suunto's Top one was my Vytec and the bottom one was my Vyper. Both are calibrated for sea water but even if they wernt it wouldent explain the 14m diferance in the two printouts. The error was still present in the shalows. Look at the 6m stop depth, its saying I was at 20m. The Vytec depth sensor had failed and was replaced under warrentee. ATB Mark Chase __________________ See my "Doing It Chasey" video where I'm locked into a padded room, naked, with two ball bearings and within an Hour, I manage to lose one and break the other!!! Kevin Juergensen 16/11/08 [/quote] Last edited by Mark Chase : 3rd November 2006 at 12:35.
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3rd November 2006, 20:09	#18 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,873	Re: Onboard vs. Offboard Deco Quote: (Originally Posted by Mark Chase) As you can see from the printouts ther units were Suunto's Top one was my Vytec and the bottom one was my Vyper. Both are calibrated for sea water but even if they wernt it wouldent explain the 14m diferance in the two printouts. The error was still present in the shalows. Look at the 6m stop depth, its saying I was at 20m. The Vytec depth sensor had failed and was replaced under warrentee. ATB Mark Chase Hi Mark, now I see. I was fading at the end of that last post as you can see from the botched multiquote, and then went to bed. So the Suunto depth sensor died? Is this a common problem? I thought they were supposed to be decent quality. I have an Uwatec, which hasn't given me any trouble other than blanking the depth deeper than 100M. It came back as soon as I ascended above 100M. I don't know anybody who has anything else, and everybody seems to think they're reliable to 100M, so I have no reason not to trust mine. But if I were doing big dives on a regular basis, I would probably have a back up comp as well the BT. It also occured to me after reading the posts again, that you regularly dive in overhead environments in the 70+M range and I don't. But again, if I did, I would bring another stand alone comp. But back to the issue of an inline sensor or not, the 15 minute deco discrepancy on a big dive is something I would sweat, it's important. Can you clarify which VR was inline, the short deco time or the longer? Thanks, -Andy
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4th November 2006, 07:24	#19 (permalink)
Mark Chase RBW Member Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Jan 2005 Location: Kent Posts: 2,858	Re: Onboard vs. Offboard Deco Quote: (Originally Posted by silent running) Hi Mark, now I see. I was fading at the end of that last post as you can see from the botched multiquote, and then went to bed. So the Suunto depth sensor died? Is this a common problem? I thought they were supposed to be decent quality. I have an Uwatec, which hasn't given me any trouble other than blanking the depth deeper than 100M. It came back as soon as I ascended above 100M. I don't know anybody who has anything else, and everybody seems to think they're reliable to 100M, so I have no reason not to trust mine. But if I were doing big dives on a regular basis, I would probably have a back up comp as well the BT. It also occured to me after reading the posts again, that you regularly dive in overhead environments in the 70+M range and I don't. But again, if I did, I would bring another stand alone comp. But back to the issue of an inline sensor or not, the 15 minute deco discrepancy on a big dive is something I would sweat, it's important. Can you clarify which VR was inline, the short deco time or the longer? Thanks, -Andy The depth sensors on all dive computers are a week link. They are cheep low quality items in the world of pressure sensors and they are easily damaged by dropping the computer. Having dived with three dive computers and seen three different depth readings displayed I don't think they are particularly accurate even when they do work. I don't know of any specific issue with the Suunto but i have herd many tails of dodgy depth sensors generaly. In line VR3 always ran shorter than the stand alone unit. Usually between 5 -15mins. Both VR3s were capable of PP02 monitoring and i would swap their duties around occasionally jut to make sure they both worked OK and the discrepancy remained. It didn't bother me over the period of 80mins+ deco. Id usually sit out the extra time and surface as soon as it cleared where as before i had an integrated I would clear the VR3 then add on a bit just in case so i was probably doing 10mins extra on top of that again. Clearing deco a few min quicker using it in line is very low down on my list of priorities. I am much more interested in its role as an independent back up PP02 monitor and for calculation of deco following a problem. I have never been in a hurry to get out of the water unless staying in has been bad for my health. ATB Mark CHase __________________ See my "Doing It Chasey" video where I'm locked into a padded room, naked, with two ball bearings and within an Hour, I manage to lose one and break the other!!! Kevin Juergensen 16/11/08 [/quote]
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4th November 2006, 08:59	#20 (permalink)
denzel Holiday diver Current Rebreather/s: Inspiration Classic Other Rebreather/s: Not Bought Yet Join Date: Aug 2005 Location: Perth! Posts: 358	Re: Onboard vs. Offboard Deco Offboard. KISS. Q's? Denz. PS Mark, is there any piece of equipment that doesn't break in your hands? __________________ My deepest so far, 558.50 mtr, my rig a LF90D...
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