UTD Ratio deco discussion

[stuartv]

Depth is not deco time to you because you're not using RD. If you're using RD, then depth and time spent at it is closely related to your deco time. Perhaps it's possible for you to get 30 min or less of deco time and do a dive to 160' with VPM-B or Buhlmann GFs

So, a dive to 160' at 6000' elevation, using RD, for 1 minute would result in more than 30 minutes of deco? Well, I give it credit for being very conservative....

 

[boulderjohn]

John, what does the altitude correction do to your profile? Any idea what it was based on? I know it's far more rare than sea level but were there studies done on buhlmann at altitude? Again, I have no real experience deco diving at altitude.

I compared two profiles that were identical except for elevation in post #172. The one at 6,000 feet added 8 minutes. Check the post for the complete difference in time distribution. Because the impact of elevation increases the closer you get to the surface, the primary impact is in the length of the shallow stops.

 

[mikeny9]

The dive I planned and then talked about does not ever exceed 160', so the average obviously does not exceed 160'.

You're really confusing me. You mentioned:

I just planned for 15 minutes at 200' (elevation: sea level), with 21/20 for back gas and EAN70 for deco gas, and I only get 25 minutes of deco... That's using Buhlmann with GF50/80.

What dive are you talking about that doesn't ever exceed 160' that you planned? Did you share it?

The deco time would only be more than 30 minutes if you plan it using RD. You said earlier that RD is not the reason you couldn't do the dive. That it would still be too much deco time using Buhlmann. You were wrong.

You're not comparing apples to apples. You changed the BT to 15 min and the depth to 200' at 0 ft elevation. Also I think there's a difference in what we are considering "deco time." I consider it the time spent from 50% of your depth up to the surface. Using MultiDeco set to 50/80, 6000ft of elevation, 21/35 for back gas and 50% for deco gas, a dive to 160' for 25 min gives 46 min of deco. A dive to 200' at 0 ft of elevation gives around 35 min of deco time. Both of those are well over 30 min. If I was using GFs I still wouldn't do this dive. That was the point I was trying to make when I said earlier, "RD is not the reason I couldn't do the dive."

Apparently, it is simply your UTD training that would let you dive to 160' at sea level but only let you dive to 130' at 6000' elevation.

Looking at the same dive in MultiDeco, I wouldn't do that dive with Buhlmann GFs either, I pray for those who would.

So, a dive to 160' at 6000' elevation, using RD, for 1 minute would result in more than 30 minutes of deco?

I'm not sure how you came to that conclusion, but the answer is definitely "no." I'll chalk this statement up to another case where people think they know more about RD when they've never taken a class or dove it. You should probably take the class and dive RD before making your own conclusions about it.

 

[boulderjohn]

I know it's far more rare than sea level but were there studies done on buhlmann at altitude?

Buhlmann's research was done primarily at altitude.

 

[boulderjohn]

This research was done in 2007, pretty recent considering Buhlmann was circa 1960's....

No.

Buhlmann's original research was published in 1983. His labs continued to work, and alterations were made well after that.

Gradient factors were added by Erik Baker much after that.

 

[boulderjohn]

I planned a dive to 130 ft for both the sea level dive and altitude dive, because 130' at 6000 ft elevation is roughly equivalent to 160' at sea level. 160' is my limit at sea level, so I changed both dives to 130'. I can't tell you how a dive to 160' at 6000 ft elevation would look like on RD, because depth adjusting 160' from sea level to altitude goes beyond the depth limit of my training.

A day ago you presented yourself as an expert on Ratio Deco in comparison to all the know-nothings who were arguing with you.

I created two profiles using Buhlmann + GFs for a dive to 160 feet, one at sea level and one at 6,000 feet. I asked you as a self-described expert on Ratio Deco to tell me what a diver would do on those dives using Ratio Deco as a guide. I am not interested in a different dive you would do instead because that one is beyond your training. If you can't tell me because you don't know enough about Ratio Deco, perhaps some other UTD diver can.

Anyone?

 

[boulderjohn]

I planned a dive to 130 ft for both the sea level dive and altitude dive, because 130' at 6000 ft elevation is roughly equivalent to 160' at sea level. 160' is my limit at sea level, so I changed both dives to 130'. I can't tell you how a dive to 160' at 6000 ft elevation would look like on RD, because depth adjusting 160' from sea level to altitude goes beyond the depth limit of my training.

Well, if this is UTD policy, it is a new one. When I was with UTD, we did all our diving at altitude, and we never made any depth adjustments because of it. Is this UTD policy, or did you impose it on the system yourself?

 

[boulderjohn]

I will keep my monkey out of this circus,

but for the sake of info.....same dive profile regardless of elevation.
180' dive, 18/45 or 15/55, 50% and O2 for deco. Set point 200', double BT then adj for depth (dive is 180 so minus 10 min).

180(3)
180-27(30)
120-2(32)
120-1(33)
110-1(34)
100-1(35)
90-2(37)
80-2(39)
70-5(44), 50%
60-5(49), 50%
50-2(51), 50%
40-2(53), 50%
30-10(63), 50%
20-10(73),100%
10-10(83), 100%

BT 27, RT 83, DT 44

You can shape the S curve and O2 anyway you'd like.

This is a RD 2.0 1:2 ratio deco profile, depth range 170-240.

OK, let's go with this and make a comparison. Here is the Buhlmann 50/80 comparison at sea level.

Elevation = 0ft
Conservatism = GF 50/80

Dec to 180ft (3) Trimix 18/45 60ft/min descent.
Level 180ft 27:00 (30) Trimix 18/45 1.14 ppO2, 66ft ead, 84ft end
Asc to 90ft (33) Trimix 18/45 -30ft/min ascent.
Stop at 90ft 1:00 (34) Trimix 18/45 0.66 ppO2, 24ft ead, 34ft end
Stop at 80ft 1:00 (35) Trimix 18/45 0.60 ppO2, 19ft ead, 29ft end
Stop at 70ft 2:00 (37) Nitrox 50 1.53 ppO2, 32ft ead
Stop at 60ft 2:00 (39) Nitrox 50 1.38 ppO2, 26ft ead
Stop at 50ft 3:00 (42) Nitrox 50 1.24 ppO2, 19ft ead
Stop at 40ft 4:00 (46) Nitrox 50 1.09 ppO2, 13ft ead
Stop at 30ft 7:00 (53) Nitrox 50 0.94 ppO2, 7ft ead
Stop at 20ft 9:00 (62) Oxygen 1.59 ppO2, 0ft ead
Stop at 10ft 16:00 (78) Oxygen 1.29 ppO2, 0ft ead
Surface (78) Oxygen -20ft/min ascent.
​

Key differences:

1. RD first stop at 120 feet; Buhlmann at 90.
2. RD time on ascent between 180-80 = 9 minutes; Bulmann = 5
3. RD 70-60 time = 10 minutes (oxygen window theory); Buhlmann = 4
4. RD total ascent time to 50 feet = 19 minutes; Buhlmann = 9
5. RD total time at last two stops = 20 minutes; Buhlmann = 25
6. RD total Run time = 83 minutes; Buhlmann = 78

Here is the Buhlmann dive at 6,000 feet. The comparison that follows it to the same UTD profile, since there is no evidence so far that there is a difference.

Dec to 180ft (3) Trimix 18/45 60ft/min descent.​

Level 180ft 26:53 (30) Trimix 18/45 1.14 ppO2, 66ft ead, 84ft end
Asc to 90ft (33) Trimix 18/45 -30ft/min ascent.
Stop at 90ft 1:00 (34) Trimix 18/45 0.66 ppO2, 24ft ead, 34ft end
Stop at 80ft 1:00 (35) Trimix 18/45 0.60 ppO2, 19ft ead, 29ft end
Stop at 70ft 1:00 (36) Nitrox 50 1.53 ppO2, 32ft ead
Stop at 60ft 2:00 (38) Nitrox 50 1.38 ppO2, 26ft ead
Stop at 50ft 3:00 (41) Nitrox 50 1.24 ppO2, 19ft ead
Stop at 40ft 4:00 (45) Nitrox 50 1.09 ppO2, 13ft ead
Stop at 30ft 6:00 (51) Nitrox 50 0.94 ppO2, 7ft ead
Stop at 20ft 7:00 (58) Oxygen 1.59 ppO2, 0ft ead
Stop at 10ft 29:00 (87) Oxygen 1.29 ppO2, 0ft ead
Surface (87) Oxygen -20ft/min ascent.

Key differences:

1. RD first stop at 120 feet; Buhlmann at 90.
2. RD time on ascent between 180-80 = 9 minutes; Bulmann = 5
3. RD 70-60 time = 10 minutes (oxygen window theory); Buhlmann = 3
4. RD total ascent time to 50 feet = 19 minutes; Buhlmann = 8
5. RD total time at last two stops = 20 minutes; Buhlmann = 36
   
6. RD total Run time = 83 minutes; Buhlmann = 87

The primary difference between Buhlmann at altitude and RD at altitude is that Bulmann adds 9 minutes to its total run time, resulting in 16 more minutes of deco on the last two stops.

Key Idea for Me: The RD algorithm is much more a deep stop algorithm than is Buhlmann, and that difference is even greater at altitude.

 

[mikeny9]

A day ago you presented yourself as an expert on Ratio Deco in comparison to all the know-nothings who were arguing with you.

In comparison to the "know-nothings" I'd say I definitely understand more than them. However, I'm far from an expert on ratio deco, my training limits I've described should give you an indication of that. I'm curious why you can't pick a dive that's within the limits of my training to discuss though. Perhaps because it won't suit your argument?

Well, if this is UTD policy, it is a new one. When I was with UTD, we did all our diving at altitude, and we never made any depth adjustments because of it. Is this UTD policy, or did you impose it on the system yourself?

What specifically is the new UTD policy you're referring to?

Our experiences with ratio deco classes are very different. In my courses I was explicitly taught one can't use RD strictly the same when it comes to altitude diving. We didn't talk much about why, altitude diving was beyond the limits of the course. However, it seemed fairly obvious to me that if you do a dive at altitude it's not the same as one at sea level, so obviously things will be different. I can't imagine one would use RD exactly the same way they do at sea level and at altitude, that doesn't seem like a "thinking diver" to me.

I'm not an altitude diver, but I applied the little knowledge I know about it to create profiles using what I know about RD that I think would be safe at 6000 feet to play your game. I've asked you if those were acceptable and got no reply.

 

[mikeny9]

Jay you didn't adjust that at all from sea level? Seems like a bad idea.