UTD Ratio deco discussion

[mikeny9]

I am very confused by what you did. Did you plan a dive to 160 feet using an equivalent depth of 130 feet, or did you plan a dive to 130 feet?

Here are the Buhlmann plans for a dive to 160 feet for 25 minutes on 21/35 with one deco gas, both at sea level and at altitude. Could you tell me what the new RD plans would be for those two dives? Don't worry about what your personal limitations are--I just want to know what the new RD rules are.

Elevation = 0ft
Conservatism = GF 50/80

Dec to 160ft (2) Triox 21/35 60ft/min descent.
Level 160ft 22:20 (25) Triox 21/35 1.20 ppO2, 74ft ead, 92ft end
Asc to 70ft (28) Triox 21/35 -30ft/min ascent.
Stop at 70ft 1:00 (29) Nitrox 50 1.53 ppO2, 32ft ead
Stop at 60ft 1:00 (30) Nitrox 50 1.38 ppO2, 26ft ead
Stop at 50ft 1:00 (31) Nitrox 50 1.24 ppO2, 19ft ead
Stop at 40ft 2:00 (33) Nitrox 50 1.09 ppO2, 13ft ead
Stop at 30ft 4:00 (37) Nitrox 50 0.94 ppO2, 7ft ead
Stop at 20ft 7:00 (44) Nitrox 50 0.79 ppO2, 0ft ead
Stop at 10ft 14:00 (58) Nitrox 50 0.65 ppO2, 0ft ead
Surface (58) Nitrox 50 -20ft/min ascent.

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. Ratio deco is introduced to students gradually as they progress. From what I understand, in Tech 2 (200' max depth at sea level), they introduce cascading ratio deco, which I'm not familiar with. If no one answers, and if I end up taking that class, I'll report back.

 

[stuartv]

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. Ratio deco is introduced to students gradually as they progress. From what I understand, in Tech 2 (200' max depth at sea level), they introduce cascading ratio deco, which I'm not familiar with. If no one answers, and if I end up taking that class, I'll report back.

You're certified to dive to 160', but you can only dive to 130' if you happen to want to dive in a lake that is at 6000'?? And that's because you use Ratio Deco, instead of Buhlmann (or VPM-B) and a bottom timer (or an actual dive computer)???

 

[mikeny9]

Yes. The increased deco obligation from a dive to 160' at 6000 ft of elevation is outside the limits of my training (max 30 min deco). If I used a computer with VPM-B or Buhlmann GFs I'd end up with more than 30 min of deco too. The limitation is not ratio deco, but deco time. Ratio deco allows me to figure out that the dive is beyond my limits pretty quickly without even using a computer.

 

[stuartv]

Yes. The increased deco obligation from a dive to 160' at 6000 ft of elevation is outside the limits of my training (max 30 min deco). If I used a computer with VPM-B or Buhlmann GFs I'd end up with more than 30 min of deco too. The limitation is not ratio deco, but deco time. Ratio deco allows me to figure out that the dive is beyond my limits pretty quickly without even using a computer.

Interesting. What sea level equivalent depth are you planning for when planning 160' at 6000'?

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.

 

[mikeny9]

Sure, if you pick a shorter bottom time you end up with less deco time. However, the limits are no more than 30 min of deco, no more than 15 min on 100% O2, and no average depth greater than 160' (at sea level). Because 160' at 6000 is definitely not 160' at sea level, the dive is outside the limits of my training regardless of bottom time.

 

[stuartv]

Sure, if you pick a shorter bottom time you end up with less deco time. However, the limits are no more than 30 min of deco, no more than 15 min on 100% O2, and no average depth greater than 160' (at sea level). Because 160' at 6000 is definitely not 160' at sea level, the dive is outside the limits of my training regardless of bottom time.

Before, you said you couldn't do the dive because of the limitation on deco time.

Now, you're saying it's not the deco time (since you CAN plan a dive for less than 30 minutes deco). You're saying that UTD training that certifies you to dive to 160' at sea level only certifies you to dive to 130' at 6000' of elevation? Because it's "equivalent" (in terms of deco obligation) to doing a deeper dive at sea level, even though you could stay within the deco limits and the actual depth limits of your training?

 

[mikeny9]

Before, you said you couldn't do the dive because of the limitation on deco time.

Now, you're saying it's not the deco time (since you CAN plan a dive for less than 30 minutes deco). You're saying that UTD training that certifies you to dive to 160' at sea level only certifies you to dive to 130' at 6000' of elevation? Because it's "equivalent" (in terms of deco obligation) to doing a deeper dive at sea level, even though you could stay within the deco limits and the sea level depth limits of your training?

I wouldn't do the dive at 160' for 25 min at 6000 ft of elevation because the deco time would be way more than 30 min. I've also stated I think for the third time or fourth time now, that UTD doesn't teach altitude diving in ratio deco. To be clear (again), I'm posting what I would do. Finally, yes, I wouldn't plan any dive, whether it's at altitude or sea level, if my deco time is within the limit but my average depth is greater than the limit of my training. Also, I could bounce dive to 400' and come up to 100', level off until the dive averages out to 160' and then calculate deco time, but that's stupid. My computer would let me do that, my brain won't.

 

[Patoux01]

I do, when there's value to it already and that I can bring something to it.
Claiming one is not allowed to dive in altitude because "the depth needs to be adjusted" is a very interesting view. I mean, supposedly, PADI was supposed to hand me my altitude diver card because I got certified at 300-something m altitude. Yet we did not limit the dives to 17m. We want the full way to 18

Depth is depth, deco time is deco time. Depth is not deco time. 40m at sea is the same as 40m at 8500m. What would change is the deco time. Deco does not work with depth, it works with pressure and pressure gradients.


edit: I wrote "allowed", but it's not really correct, you're just saying you wouldn't.

 

[mikeny9]

Depth is depth, deco time is deco time. Depth is not deco time. 40m at sea is the same as 40m at 8500m. What would change is the deco time. Deco does not work with depth, it works with pressure and pressure gradients.

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, I hope you don't wind up as another statistic. I'd rather err on the side of caution, depth adjust, and determine the dive is outside my limits. The argument thus far against RD was about it not working with adverse effects (i.e. getting bent at altitude). If I wouldn't do this dive, I take 0 risk compared to someone using a computer and a model. No thanks.

It's also interesting how everyone is focusing on a dive to 160' at altitude, rather than a shallower one that we could actually compare.

 

[stuartv]

I wouldn't do the dive at 160' for 25 min at 6000 ft of elevation because the deco time would be way more than 30 min. I've also stated I think for the third time or fourth time now, that UTD doesn't teach altitude diving in ratio deco. To be clear (again), I'm posting what I would do. Finally, yes, I wouldn't plan any dive, whether it's at altitude or sea level, if my deco time is within the limit but my average depth is greater than the limit of my training. Also, I could bounce dive to 400' and come up to 100', level off until the dive averages out to 160' and then calculate deco time, but that's stupid. My computer would let me do that, my brain won't.

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.

The dive I planned and then talked about does not ever exceed 160', so the average obviously does not exceed 160'. Continuing to talk about exceeding your depth limits and average depths is irrelevant and seems to only have the purpose of directing attention away from the issue: Either RD or UTD training is what would stop you from doing a 160' dive at 6000' elevation.

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. Because, somehow, even with less than 30 minutes of deco, diving to 160' is different at elevation (beyond just the change in deco time) than it is at sea level.

Which is fine. If you're happy with your training, that's really all that matters. I'm glad for the additional information you have provided, as it just confirms my own decision that I will never pursue advanced training with UTD. Based on the number of divers with TDI training that are doing WAY more advanced dives than I am, I think I will continue to be both happy and safe with my training.