80% or O2 DECO

[JeffG]

OTOH I could just do the dive on my rebreather with a fixed set point of 1.2 and get out faster than all you OC guys but again that's not a fair comparison.

but that is like carrying a couple of deco bottles. You can push the RB to 100% at 20 ft.

If I did a 150 dive with 21/35 and had a 50% bottle and a 100% bottle we would have a similar run time.

(I remember comparing times from Ratio deco vs NAUI RGBM Rebreather tables my buddy had. (I think they were NAUI anyways). We were within a couple of minutes on the dives we checked. At least thats what I thought we were checking. Heck maybe the crack I've been smoking has got me a ^%$^%4 up.)

 

[amascuba]

Yeah but let's compare apples to apples. You are throwing in a 3rd deco gas which will of course get you out quicker. Try a dive to 150ft using only 50% and 100% and see what happens. I don't have v-planner here at work so I can't post the results.
OTOH I could just do the dive on my rebreather with a fixed set point of 1.2 and get out faster than all you OC guys but again that's not a fair comparison.

The concept of closed circuit rebreathers is very good, but for my taste right now I don't trust them. That's actually a orginal thought of mine. I didn't like the idea of CCR before I even heard the term DIR.

Here is what I get with the same two programs with the same settings, except bottom gas is 21/35, depth of 150, and same bottom time of 30 min. I'll use 50%, 80% deco gases for your point of view and 50% and 100% from my point of view.

Dive 1 using mv-plan with deco gases of 50% and 80% has a run time of 58min.

Dive 2 using mv-plan with deco gases of 50% and 100% has a run time of 58min.

The only difference between the two dives is that on the 80% deco you spend 4min.@30 and 6min.@20 and on 100% you spend 4min.@30 and 5min.@20.

Dive 3 using hlplanner with deco gases of 50% and 80% has a run time of 60min.

Dive 4 using hlplanner with deco gases of 50% and 100% has a run time of 59min.

The only difference between these two dives is that the 10foot stop on 100% is one minute shorter.

Edit: Did the same dives again, but this time with 32% and 80% for deco and 50% and 100% for deco.

Dive 1 w/ mv-plan and 32% and 80% has a run time of 59min.

Dive 2 w/ mv-plan and 50% and 100% has a run time of 58min.

Dive 3 w/ hlplanner and 32% and 80% has a run time of 61min.

Dive 4 w/ hlplanner and 50% and 100% has a run time of 59min.

 

[wedivebc]

The only difference between the two dives is that on the 80% deco you spend 4min.@30 and 6min.@20 and on 100% you spend 4min.@30 and 5min.@20.

.

Not familiar with mv-plan but if it allows you to spend any time at 30ft breathing 100% I wouild get a new deco program:huh:

 

[amascuba]

Not familiar with mv-plan but if it allows you to spend any time at 30ft breathing 100% I wouild get a new deco program:huh:

Sorry, I should have made myself more clear. On the dive utilizing the deco gases that you suggested for decompression the 20ft stop was one minute longer than the dive utilizing DIR standard decompression gases. It didn't suggest utilizing 100% at 30fsw at all.

Somebody on this board mentioned MV-Plan and I've been playing with it a bit. It's not as intuitive as some of the other deco planning software, but after I took my own advice and RTFM (read the forewarned manual) , it's not that bad. It can be found at http://www.wittig.net.au/diving/mvplan.html.

I also got bored and planned the dive out with ratio deco. It's not that different from the other dives.

Ratio Deco Dive:

Depth - 150fsw
Bottom Time: 30min.

Bottom Gas: 21/35
Deco Gases: EAN50 and O2

Descend at 60ft/min. to 150fsw Run Time: 2 min. 30 sec.
Dive at 150fsw for 27 min. 30 sec. Run Time: 33 min.
Ascend at 30ft/min. to 70fsw Run Time: 32 min. 40 sec.
Switch from 21/35 to 50% for DECO.
DECO at 70fsw for 2 min. Run Time: 35 min.
Ascend at 10ft/min. to 60fsw Run Time: 36 min.
DECO at 60fsw for 2 min. Run Time: 38 min.
Ascend at 10ft/min. to 50fsw Run Time: 39 min.
DECO at 50fsw for 2 min. Run Time: 41 min.
Ascend at 10ft/min. to 40fsw Run Time: 42 min.
DECO at 40fsw for 2 min. Run Time: 44 min.
Ascend at 10ft/min. to 30fsw Run Time: 43 min.
DECO at 30fsw for 3 min. Run Time: 45 min.
Ascend at 10ft/min. to 20fsw Run Time: 46 min.
Switch from 50% to 100% for DECO.
DECO at 20fsw for 15 min. Run Time: 61 min.
Ascend at 10ft/min. to the surface. Run Time: 63 min.

I may not be totally right with ratio deco, but from what I understand of it that should be the profile. Anybody want to critique it? Never hurts to cyber-dive things like this until you understand it better.

 

[limeyx]

Sorry, I should have made myself more clear. On the dive utilizing the deco gases that you suggested for decompression the 20ft stop was one minute longer than the dive utilizing DIR standard decompression gases. It didn't suggest utilizing 100% at 30fsw at all.

Somebody on this board mentioned MV-Plan and I've been playing with it a bit. It's not as intuitive as some of the other deco planning software, but after I took my own advice and RTFM (read the forewarned manual) , it's not that bad. It can be found at http://www.wittig.net.au/diving/mvplan.html.

I also got bored and planned the dive out with ratio deco. It's not that different from the other dives.

Ratio Deco Dive:

Depth - 150fsw
Bottom Time: 30min.

Bottom Gas: 21/35
Deco Gases: EAN50 and O2
...
DECO at 20fsw for 15 min. Run Time: 61 min.
Ascend at 10ft/min. to the surface. Run Time: 63 min.

I may not be totally right with ratio deco, but from what I understand of it that should be the profile. Anybody want to critique it? Never hurts to cyber-dive things like this until you understand it better.

The ratio deco bit looks reasonable to me (bear in mind I am only really trained for a single deco gas though) but I think you'd combine the 10 and 20 foot times and do them at 20feet on 100%, then do a really slow ascent to the surface. (Possibly slicing off 2-3 mins of the stop at 20 if you do the slow ascent)

 

[amascuba]

The ratio deco bit looks reasonable to me (bear in mind I am only really trained for a single deco gas though) but I think you'd combine the 10 and 20 foot times and do them at 20feet on 100%, then do a really slow ascent to the surface. (Possibly slicing off 2-3 mins of the stop at 20 if you do the slow ascent)

That makes sense.

 

[JeffG]

DECO at 70fsw for 2 min. Run Time: 35 min.
Ascend at 10ft/min. to 60fsw Run Time: 36 min.
DECO at 60fsw for 2 min. Run Time: 38 min.
Ascend at 10ft/min. to 50fsw Run Time: 39 min.
DECO at 50fsw for 2 min. Run Time: 41 min.
Ascend at 10ft/min. to 40fsw Run Time: 42 min.
DECO at 40fsw for 2 min. Run Time: 44 min.
Ascend at 10ft/min. to 30fsw Run Time: 43 min.
DECO at 30fsw for 3 min. Run Time: 45 min.

Doesn't look right to me, but then it could be how you put the runtime numbers.

from 70-30 you should have 15min of deco. Your runtime says 10 (+2 for the 70 stop) so 12, but if I add your stops and ascents I get 15mins.


If you are using 100% at 20 feet, you only have to do 8 min (15mins is for 50%)

 

[amascuba]

Doesn't look right to me, but then it could be how you put the runtime numbers.

from 70-30 you should have 15min of deco. Your runtime says 10 (+2 for the 70 stop) so 12, but if I add your stops and ascents I get 15mins.


If you are using 100% at 20 feet, you only have to do 8 min (15mins is for 50%)

I think I fubered on my run times. The way that I understand it though is that you count the ascent as part of your deco for each o2 segment. Is that correct?

So the 100% o2 segment is only half of the 50% segment? For some reason I read into it that each o2 segment would be half of the bottom time for depth up to 150fsw.

 

[Jason B]

My understanding of the ratio deco (AG's paper on it anyway) is that for 150ft your O2 time is half your bottom time (in this case 15 minutes).
Your 70-30ft stops is also 15 minutes. Since you are wanting to take advantage of the O2 window, you should use and S curve which will make the stops for this segment be:
70ft for 4 min
60ft for 4 min
50ft for 2 min
40ft for 2 min
30ft for 3 min

 

[JeffG]

I think I fubered on my run times. The way that I understand it though is that you count the ascent as part of your deco for each o2 segment. Is that correct?

Yes. Personally, I would steal some time from the middle part 60 and 50 and move it down to the 40 and 30 time slots. But that's just me.

So the 100% o2 segment is only half of the 50% segment? For some reason I read into it that each o2 segment would be half of the bottom time for depth up to 150fsw.

The time is based on 50%. Using O2 cuts that in half. Likewise, having to use backgas doubles the time.