Are dive computers making bad divers?

[CuzzA]

Looks like we have a new winner folks.

 

[KenGordon]

Don't blame Ross. The program on which ScubaBoard currently runs does not handle that sort of thing very well at all.

This is some simple text typed in the iPad notes app with a multi deco plan pasted on the end to see if two stage pasting helps.

Answer, no it does not.

 

[scubadada]

How about trying the following more true-to-life profile instead. You know your total bottom time at 130ft is 10 minutes so start with that deepest part first.

8 minutes at 130 feet
8 minutes at 100 feet
8 minutes at 70 feet

The above profile gives you 24 minutes which is closer to the total time of 25 minutes you have calculated. Nowhere in that progression have you pushed into deco.

OK, descend to 130 feet and spend 8 minutes, ascend to 100 feet and spend 8 minutes, ascend to 70 feet and spend 8 minutes, then ascend for the surface. I used EAN 28 so that the pO2 would be 1.4. Using 40/85, this is a deco dive. Using 45/95, this is arguably a no stop with a safety stop. I think we all get what averaging is, I would not use it on anything that was close to a deco dive, I'll stick with my computer.

MultiDeco 4.10 by Ross Hemingway,
ZHL code by Erik C. Baker.
Decompression model: ZHL16-C + GF
DIVE PLAN
Surface interval = 2 day 0 hr 0 min.
Elevation = 0ft
Conservatism = GF 40/85
Dec to 130ft (2) Nitrox 28 60ft/min descent.
Level 130ft 7:50 (10) Nitrox 28 1.38 ppO2, 116ft ead
Asc to 100ft (11) Nitrox 28 -24ft/min ascent.
Level 100ft 8:00 (19) Nitrox 28 1.13 ppO2, 88ft ead
Asc to 70ft (20) Nitrox 28 -24ft/min ascent.
Level 70ft 8:00 (28) Nitrox 28 0.87 ppO2, 61ft ead
Asc to 30ft (30) Nitrox 28 -24ft/min ascent.
Stop at 30ft 0:50 (31) Nitrox 28 0.53 ppO2, 24ft ead
Stop at 20ft 1:00 (32) Nitrox 28 0.45 ppO2, 15ft ead
Stop at 10ft 3:00 (35) Nitrox 28 0.36 ppO2, 6ft ead
Surface (35) Nitrox 28 -20ft/min ascent.
OTU's this dive: 34
CNS Total: 12.8%
49.7 cu ft Nitrox 28
49.7 cu ft TOTAL
　
DIVE PLAN COMPLETE


DIVE PLAN
Surface interval = 2 day 0 hr 0 min.
Elevation = 0ft
Conservatism = GF 45/95
Dec to 130ft (2) Nitrox 28 60ft/min descent.
Level 130ft 7:50 (10) Nitrox 28 1.38 ppO2, 116ft ead
Asc to 100ft (11) Nitrox 28 -24ft/min ascent.
Level 100ft 8:00 (19) Nitrox 28 1.13 ppO2, 88ft ead
Asc to 70ft (20) Nitrox 28 -24ft/min ascent.
Level 70ft 8:00 (28) Nitrox 28 0.87 ppO2, 61ft ead
Asc to 20ft (30) Nitrox 28 -24ft/min ascent.
Stop at 20ft 0:25 (31) Nitrox 28 0.45 ppO2, 15ft ead
Stop at 10ft 1:00 (32) Nitrox 28 0.36 ppO2, 6ft ead
Surface (32) Nitrox 28 -20ft/min ascent.
OTU's this dive: 34
CNS Total: 12.7%
47.9 cu ft Nitrox 28
47.9 cu ft TOTAL
　
DIVE PLAN COMPLETE

 

[CAPTAIN SINBAD]

So I would like to see some justification for the claim that Captain Sinbad's plan does not go into deco. Under what algorithm is that true? Are you saying that because you left the bottom within the limits you are OK? Leaving the bottom within limits only works if you head for the surface at the rate prescribed by the tables.

---------- Post added December 18th, 2015 at 05:16 PM ----------



For me, only when I'm narked.

John: This was from Depth Averaging seminar conducted by the same group of people you and I often talk about outside this thread. After you posted computer printouts, I sent them to the instructor who taught this seminar to see what he thinks. I have not heard back. To be fair to them, the calculation error there is on my part because the agencies that teach this do this between 60 - 100 feet. As you can see from the max depth of 130, we are playing way outside their suggested territory.

 

[packrat12]

John: This was from Depth Averaging seminar conducted by the same group of people you and I often talk about outside this thread. After you posted computer printouts, I sent them to the instructor who taught this seminar to see what he thinks. I have not heard back. To be fair to them, the calculation error there is on my part because the agencies that teach this do this between 60 - 100 feet. As you can see from the max depth of 130, we are playing way outside their suggested territory.

The problem I see is that this is defined to a narrow range which the air limits are around the NDL limits for most divers. 25 min at 100' is a fairly long dive recreational dive near most normal air limits. Add in the differences with normal changes in depth and you may get off-gassing benefits and not bend (or you still may bend). This, however, is taking advantage of certain normal diving behaviors in diving to be safe, not decompression limits.

Accordingly I could say that I will dive the following within the 'new suggested territory':

100' for 26 min and ascend to 60' for 9 min. Overall time 35 min ave 80'. Add in descent/ascent times ~5 gives 40 min total time, INCLUDING ascent (which is not the number presented in the table (BT)) which is the NDL for 80'.

Multi Deco comes up with: 1st deco is at 30' for 1 min, 2nd deco stop is at 20' for 19min for a total of 20 min deco and a runtime of 59 min.

MultiDeco 4.10 by Ross Hemingway,
ZHL code by Erik C. Baker.

Decompression model: ZHL16-C + GF

DIVE PLAN
Surface interval = 5 day 0 hr 0 min.
Elevation = 0ft
Conservatism = GF 30/85

Dec to 100ft (1) Air 60ft/min descent.
Level 100ft 24:20 (26) Air 0.85 ppO2, 100ft ead
Asc to 60ft (27) Air -24ft/min ascent.
Level 60ft 9:00 (36) Air 0.59 ppO2, 60ft ead
Asc to 40ft (37) Air -24ft/min ascent.
Stop at 40ft 0:30 (38) Air 0.46 ppO2, 40ft ead
Stop at 30ft 1:00 (39) Air 0.40 ppO2, 30ft ead
Stop at 20ft 19:00 (58) Air 0.34 ppO2, 20ft ead
Surface (59) Air -20ft/min ascent.


This most definitely is not a safe way of diving even with your new 'suggested territory'. Adherents to this philosophy may not be getting bent only through luck and definitely not by following recognized decompression theories.

BTW, the profile I presented is similar to one I have dove several times. When going to the props on the Spiegel Grove with a rec diver, I will follow the upper deck at ~80' and then descend to the props at ~135 for a tour then head back up. There is little to no time to tour the rest of the depths even with a computer. We get no where near the times an 'average depth' calculation would give. Following this philosophy will get you bent.

 

[doctormike]

Hey, I don't know much about flying, but I'm guessing that in the old days of aviation, it was probably harder to fly significant distances without modern avionics. However, I'll bet that those pilots were much better trained on how to calculate the various flight paths and trajectories in their heads, using analog printouts like maps and tables.

Anyone want to buy tickets on an airline that does it the old fashioned way, without computers and GPS and weather systems, etc...? You know, because the pilots are better?

 

[Storker]

Again, in the immortal words of Winnie-the-Pooh: Both, please. What I'd really prefer would be a machine with all the bells and whistles you can get, but with pilots who are proficient enough to fly the plane even if those gizmos died.

 

[packrat12]

Again, in the immortal words of Winnie-the-Pooh: Both, please. What I'd really prefer would be a machine with all the bells and whistles you can get, but with pilots who are proficient enough to fly the plane even if those gizmos died.

Well I am a Certified Flight Instructor also. I can fly with a map and dead reckoning but I still have must say that if my computer failed while within NDL, I would call my dive. I can say that tables offer nothing to the diver. Not much to it.

 

[doctormike]

Again, in the immortal words of Winnie-the-Pooh: Both, please. What I'd really prefer would be a machine with all the bells and whistles you can get, but with pilots who are proficient enough to fly the plane even if those gizmos died.

Right, but that's not what we are discussing, at least as far as I can tell. The OP's question was whether or not HAVING a computer makes someone a bad diver. No one is saying that because you have a computer, or because you fly the computer during your dive, that excludes an understanding of decompression technology or tables or anything else.

I plan my deco on a slate, strap the slate to my arm, and it's there for the rare case of computer failure. But it's not the best way to plan a dive, or to execute a dive, when we have better options. Because - as I have said before - the slate has no idea what your dive profile actually is. It's INACCURATE information. So while it's a good fallback in case of a computer failure, it's NOT a good way to dive.

And the latest posts by the OP suggested specifically NOT using a computer, but rather relying on doing math in your head by estimating the time you spend during the dive at various depths.

Sorry, I don't see how computers make bad divers - getting back to the original question. And I wouldn't fly on a plane in 2015 with a pilot who is aware of the existence of avionics, has access to them, but refuses to use them, no matter how good a pilot they are.

 

[boulderjohn]

John: This was from Depth Averaging seminar conducted by the same group of people you and I often talk about outside this thread. After you posted computer printouts, I sent them to the instructor who taught this seminar to see what he thinks. I have not heard back. To be fair to them, the calculation error there is on my part because the agencies that teach this do this between 60 - 100 feet. As you can see from the max depth of 130, we are playing way outside their suggested territory.

I assumed as much. That is the same agency that taught me depth averaging for decompression diving. I have to admit that only two of the people who got bent while I was diving with that agency made clear mistakes in depth averaging, which we only knew about because one of them was using a computer in gauge mode, and they were able to see after they got bent how far off they were. I have not dived with anyone from that agency in years.

That also tells me what algorithm they were using--theirs.

Since the belief that the human brain never makes computational errors (while computers do with some regularity) is a foundation of their belief system, it will be interesting to hear their response.