Onboard vs. Offboard Deco

PaulTG2 · 2nd November 2006, 13:29

Hello,

I am currently in the process of purchasing a CCR and have been tossing around the issue of onboard vs offboard decompression. I was wondering what people's overall thoughts were on this.

I believe I've settled on not having onboard decompressions and going with a wrist computer to do it. The primary reason is that, as happens from time to time, the rebreather has a problem and I decide to do a dive or two on OC until the Rebreather is fixed.

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

If you use onboard deco computers how do you handle situation where you have an OC dive -- or perhaps a dive on another rebreather -- when you're rebreather tanks.

Sincerely,

Paul

Dave Crampton · 2nd November 2006, 13:48

You can get computers which come with the Rebreather like the Vision I beleive. You can also buy computers which plug into the RB and either use a fourth cell to monitor PPo2, like the HS Explorer or the DeltaP VR3/2. There are also computers which plug into all three standard cells like the Sheerwater. With these last two I know you can disconnect them and use with OC, if you buy then with that configuration. The SHeerwater can be hard wired or come with a disconnectable lead.

If the main reason your doing this is because you think the Rebreather might be offline for a while meaning O/C diving why don't you go for a more reliable RB?

Dave C

Ben Field · 2nd November 2006, 13:50

Why not both?

VR3, Shearwater and HS Explorer (I think) can be unplugged and used for OC.... if you must...

I thought part of the "fun" was sitting on the boat while everyone else dives trying to rewire your rebreather with a Rusty Leatherman tool and a Soldering Iron with a tip like a snow plough

Seriously... I just use a Timer and Tables on those very rare occasions or if the Surface Interval is long enough drag the Vyper out of tool box and use that.

BEN

Mark Chase · 2nd November 2006, 14:22

Depends on your diving but an integrated computer that monitors your PP02 can save a bit of deco time and if covers screw ups as well. Like forgetting to change the set point, (not that i would ever do such a silly thing

)

What ever you chose you will need another computer to back up the primary so I chose one inboard and one off board on my classic.

This became irritating because the inboard was always clearing before the off board but now I have (or will when i get the cable sorted) my back up inboard as well. When i need it for OC I just unplug it from the unit and use it.

I was using two VR3's now i have a Hamerhead primary controller with on board deco and a Sherewater plumbed in as back up.

ATB

Mark Chase

O.C.Diver · 2nd November 2006, 14:25

Quote: (Originally Posted by PaulTG2)

Hello,

I am currently in the process of purchasing a CCR and have been tossing around the issue of onboard vs offboard decompression. I was wondering what people's overall thoughts were on this. Paul

That is exactly what I do. I used to use a VR3 with cell for my deco info. After doing a number of dives with constant PO2 computers, I came to the conclusion there was very little difference in the deco time if you were using the same computer in PO2 versus external cell mode. I now only use a Cochran EMC-20H for deco and need only monitor the display and HUD for PO2. Having them separate also eliminates losing all information in 1 system failure!

Ted

***diverklondike*** · 2nd November 2006, 18:23

Here are my thoughts on the subject.... I carry both.... It may be a little anal or a lot at that matter but I sleep very well knowing that I have a couple fall backs...

My onboard is provided via my Hammerhead... One of the benifits of this is that if I were to go SCR for some reason the onboard computer is always calculating deco based on what's in the loop.

My offboard is provided via a VR3.

I agree as OCDiver commented that there is little advantage as it applies to deco. In a bailout situation that would not always be the case particularly if an SCR approach is part of yor plan.

Dive Safe

Mark

viscya · 2nd November 2006, 18:36

Mark,

Assuming your off board computer is a multi-gas computer, couldn't you set one of the gasses for the average of your SCR mix?

silent running · 2nd November 2006, 18:57

Hello Paul, the benefits of an onboard deco computer are minimal, IMHO.
Yes Mark is right, with an onboard deco comp you will never have to worry about changing set point on both the CCR and the computer. So now you only have to push one button instead of 2. This is not enough to justify the additional complexity of an on board deco comp, IMHO.

Onboard deco systems have multiple interfaces with the unit-sensors, solenoids, tempsticks, power switch-and thus more possibility for bugs. None of these interfaces seem really vital and take away some of the diver's options, like being able to overide the solenoid firing. You also have to like the deco alg that comes with the unit, another lack of flexability. You get a measure of convenience, but you give up some freedom, just in like any other aspect of life.

If your CCR can maintain set point well, why add another level of complexity by linking the comp and the unit? Whether you're diving MCCR or ECCR, I see no reason to add complexity anytime you can avoid it. KISS applys to ECCR just as much, if not more so, than MCCR. Too much convenience can cause complacency, too much complexity means extra effort to solve a problem, which is not any benefit in a crisis. -Andy

silent running · 2nd November 2006, 19:00

Quote: (Originally Posted by viscya)

Mark,

Assuming your off board computer is a multi-gas computer, couldn't you set one of the gasses for the average of your SCR mix?

I always keep that average mix in my OC gas list on my HE for just that purpose...

Mark Chase · 2nd November 2006, 22:05

Quote: (Originally Posted by silent running)

Hello Paul, the benefits of an onboard deco computer are minimal, IMHO.
Yes Mark is right, with an onboard deco comp you will never have to worry about changing set point on both the CCR and the computer. So now you only have to push one button instead of 2. This is not enough to justify the additional complexity of an on board deco comp, IMHO.

Onboard deco systems have multiple interfaces with the unit-sensors, solenoids, tempsticks, power switch-and thus more possibility for bugs. None of these interfaces seem really vital and take away some of the diver's options, like being able to overide the solenoid firing. You also have to like the deco alg that comes with the unit, another lack of flexability. You get a measure of convenience, but you give up some freedom, just in like any other aspect of life.

If your CCR can maintain set point well, why add another level of complexity by linking the comp and the unit? Whether you're diving MCCR or ECCR, I see no reason to add complexity anytime you can avoid it. KISS applys to ECCR just as much, if not more so, than MCCR. Too much convenience can cause complacency, too much complexity means extra effort to solve a problem, which is not any benefit in a crisis. -Andy

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

2nd November 2006, 13:29	#1 (permalink)
PaulTG2 Custom Title Allowed! Current Rebreather/s: Megalodon Classic Kiss Other Rebreather/s: Sport Kiss Join Date: Mar 2006 Location: Virginia, USA Posts: 325	Onboard vs. Offboard Deco Hello, I am currently in the process of purchasing a CCR and have been tossing around the issue of onboard vs offboard decompression. I was wondering what people's overall thoughts were on this. I believe I've settled on not having onboard decompressions and going with a wrist computer to do it. The primary reason is that, as happens from time to time, the rebreather has a problem and I decide to do a dive or two on OC until the Rebreather is fixed. What are people's thoughts on onboard vs offboard decompression. If you use onboard deco computers how do you handle situation where you have an OC dive -- or perhaps a dive on another rebreather -- when you're rebreather tanks. Sincerely, Paul
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2nd November 2006, 13:48	#2 (permalink)
Dave Crampton CK #051 Current Rebreather/s: Classic Kiss Other Rebreather/s: Join Date: Apr 2005 Location: Bury St Edmunds, UK Posts: 278	Re: Onboard vs. Offboard Deco You can get computers which come with the Rebreather like the Vision I beleive. You can also buy computers which plug into the RB and either use a fourth cell to monitor PPo2, like the HS Explorer or the DeltaP VR3/2. There are also computers which plug into all three standard cells like the Sheerwater. With these last two I know you can disconnect them and use with OC, if you buy then with that configuration. The SHeerwater can be hard wired or come with a disconnectable lead. If the main reason your doing this is because you think the Rebreather might be offline for a while meaning O/C diving why don't you go for a more reliable RB? Dave C
(Offline)

2nd November 2006, 13:50	#3 (permalink)
Ben Field CK+Shearwater Current Rebreather/s: Classic Kiss Other Rebreather/s: Sport Kiss Join Date: Aug 2005 Location: London, England Posts: 1,452	Re: Onboard vs. Offboard Deco Why not both? VR3, Shearwater and HS Explorer (I think) can be unplugged and used for OC.... if you must... I thought part of the "fun" was sitting on the boat while everyone else dives trying to rewire your rebreather with a Rusty Leatherman tool and a Soldering Iron with a tip like a snow plough Seriously... I just use a Timer and Tables on those very rare occasions or if the Surface Interval is long enough drag the Vyper out of tool box and use that. BEN __________________ www.hugsac.org.uk Beware Fridge Suck
(Online)

2nd November 2006, 14:22	#4 (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: 2,418	Re: Onboard vs. Offboard Deco Depends on your diving but an integrated computer that monitors your PP02 can save a bit of deco time and if covers screw ups as well. Like forgetting to change the set point, (not that i would ever do such a silly thing ) What ever you chose you will need another computer to back up the primary so I chose one inboard and one off board on my classic. This became irritating because the inboard was always clearing before the off board but now I have (or will when i get the cable sorted) my back up inboard as well. When i need it for OC I just unplug it from the unit and use it. I was using two VR3's now i have a Hamerhead primary controller with on board deco and a Sherewater plumbed in as back up. ATB Mark Chase __________________ 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)

2nd November 2006, 14:25	#5 (permalink)
O.C.Diver Helium Addict Current Rebreather/s: Classic Kiss Other CCR Home Build Other Rebreather/s: Not Bought Yet Other CCR Home Build Join Date: Mar 2006 Location: Salisbury MD USA Summers; Wandering Florida Winters Posts: 213	Re: Onboard vs. Offboard Deco Quote: (Originally Posted by PaulTG2) Hello, I am currently in the process of purchasing a CCR and have been tossing around the issue of onboard vs offboard decompression. I was wondering what people's overall thoughts were on this. Paul That is exactly what I do. I used to use a VR3 with cell for my deco info. After doing a number of dives with constant PO2 computers, I came to the conclusion there was very little difference in the deco time if you were using the same computer in PO2 versus external cell mode. I now only use a Cochran EMC-20H for deco and need only monitor the display and HUD for PO2. Having them separate also eliminates losing all information in 1 system failure! Ted __________________ Consider this my opinion.......sometimes I'm even right, but remember.........YMMV. Ted Green Charter Boat "OC Diver" http://www.ocdiver.com
(Offline)

2nd November 2006, 18:23	#6 (permalink)
*diverklondike* Moderator Current Rebreather/s: Inspiration Classic Other CCR Other Rebreather/s: Inspiration Classic Other CCR Join Date: Oct 2005 Location: Delaware, USA Posts: 1,439	Re: Onboard vs. Offboard Deco Here are my thoughts on the subject.... I carry both.... It may be a little anal or a lot at that matter but I sleep very well knowing that I have a couple fall backs... My onboard is provided via my Hammerhead... One of the benifits of this is that if I were to go SCR for some reason the onboard computer is always calculating deco based on what's in the loop. My offboard is provided via a VR3. I agree as OCDiver commented that there is little advantage as it applies to deco. In a bailout situation that would not always be the case particularly if an SCR approach is part of yor plan. Dive Safe Mark
(Online)

2nd November 2006, 18:36	#7 (permalink)
viscya Wrecking Crew Current Rebreather/s: Classic Kiss Other Rebreather/s: Join Date: Oct 2005 Location: Marlton New Jersey Posts: 140	Re: Onboard vs. Offboard Deco Mark, Assuming your off board computer is a multi-gas computer, couldn't you set one of the gasses for the average of your SCR mix? __________________ "There is nothing majestic or dignified about being left to silently rot and collapse under heaps of old fishing net forgotten and unappreciated in dark and unvisited waters." DrMike
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2nd November 2006, 18:57	#8 (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: 1,748	Re: Onboard vs. Offboard Deco Hello Paul, the benefits of an onboard deco computer are minimal, IMHO. Yes Mark is right, with an onboard deco comp you will never have to worry about changing set point on both the CCR and the computer. So now you only have to push one button instead of 2. This is not enough to justify the additional complexity of an on board deco comp, IMHO. Onboard deco systems have multiple interfaces with the unit-sensors, solenoids, tempsticks, power switch-and thus more possibility for bugs. None of these interfaces seem really vital and take away some of the diver's options, like being able to overide the solenoid firing. You also have to like the deco alg that comes with the unit, another lack of flexability. You get a measure of convenience, but you give up some freedom, just in like any other aspect of life. If your CCR can maintain set point well, why add another level of complexity by linking the comp and the unit? Whether you're diving MCCR or ECCR, I see no reason to add complexity anytime you can avoid it. KISS applys to ECCR just as much, if not more so, than MCCR. Too much convenience can cause complacency, too much complexity means extra effort to solve a problem, which is not any benefit in a crisis. -Andy
(Offline)

2nd November 2006, 19:00	#9 (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: 1,748	Re: Onboard vs. Offboard Deco Quote: (Originally Posted by viscya) Mark, Assuming your off board computer is a multi-gas computer, couldn't you set one of the gasses for the average of your SCR mix? I always keep that average mix in my OC gas list on my HE for just that purpose...
(Offline)

2nd November 2006, 22:05	#10 (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: 2,418	Re: Onboard vs. Offboard Deco Quote: (Originally Posted by silent running) Hello Paul, the benefits of an onboard deco computer are minimal, IMHO. Yes Mark is right, with an onboard deco comp you will never have to worry about changing set point on both the CCR and the computer. So now you only have to push one button instead of 2. This is not enough to justify the additional complexity of an on board deco comp, IMHO. Onboard deco systems have multiple interfaces with the unit-sensors, solenoids, tempsticks, power switch-and thus more possibility for bugs. None of these interfaces seem really vital and take away some of the diver's options, like being able to overide the solenoid firing. You also have to like the deco alg that comes with the unit, another lack of flexability. You get a measure of convenience, but you give up some freedom, just in like any other aspect of life. If your CCR can maintain set point well, why add another level of complexity by linking the comp and the unit? Whether you're diving MCCR or ECCR, I see no reason to add complexity anytime you can avoid it. KISS applys to ECCR just as much, if not more so, than MCCR. Too much convenience can cause complacency, too much complexity means extra effort to solve a problem, which is not any benefit in a crisis. -Andy 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 __________________ 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)

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