Suunto Cobra vs. Vytec profile inconsistent

[hdugan]

Tissue loading is dependent on blood flow. An increase in SAC rate may be an indication of a higher work load which would require an increase in blood flow.

While loading is dependant on the available blood flow, As in a blood vessel rich tissue compared to a low vessel ltissue.

It is far from settled if exersize has any effect on loading. If it did, then swimming as hard as possible while on a deco hang would be a standard MO.

 

[Scared Silly]

As I noted in my original post "IIRC" - "if I recall correctly" I read something about an algorithm that factors in one breathing rate. I thought it was Suunto's model but it may have been UWATEC's model (the only two computers I have used). It has been a while so take my post with a grain of salt which is exactly how "IIRC" should be interpreted.

 

[elan]

As I noted in my original post "IIRC" - "if I recall correctly" I read something about an algorithm that factors in one breathing rate. I thought it was Suunto's model but it may have been UWATEC's model (the only two computers I have used). It has been a while so take my post with a grain of salt which is exactly how "IIRC" should be interpreted.

I heard something I think about UWATEC, I believe it was Galileo Sol that was trying to factor in the pulse into the algorithm

 

[hdugan]

As I noted in my original post "IIRC" - "if I recall correctly" I read something about an algorithm that factors in one breathing rate. I thought it was Suunto's model but it may have been UWATEC's model (the only two computers I have used). It has been a while so take my post with a grain of salt which is exactly how "IIRC" should be interpreted.

That's even more disturbing than You being wrong! :shocked2:

 

[SeahorseDeb]

Many questions and observations, lots of which were answered by some of the participants. So, all those answered, are assumed except one: My computer went into deco. No misunderstanding it. It told me I need to do 10 minutes, which is really quite strange since research shows that stairstep deco's at deep levels i.e. half of the deepest depth have not been proven beyond a reasonable doubt to prevent DCI or DCS. I saw the warning. Since I ignored it, it went into "error" message and wanted to deline me to do another dive for 24 hours. Again I must say this, while I bought my computer to provide many valuable functions and prevent DCS and DCI, I knew I would be safe because I had not exceeded the navy dive tables. I am not a negligent person nor will I be -ever. Just want you buddies out there who are watching this thread to know that.

 

[Willar]

What is the data collection interval setting on the 2 computers? Every 30 seconds? 1 Minute? 2 Minutes? This setting affects how often it records data which is later uploaded to SDM. This data gives the graph to view at home. However, it is NOT a complete picture of your dive, it is a series of data points collected at a standard interval. However, during a dive the computer computes your profile, NDL, safety stop, and deco stop based on CONTINUOUS data calculations in real time during the dive.

I would suggest that you both incurred the extended safety stop due to a rate of rise violation. Suunto prefers a 'safe' rate of rise of 30 FPS, any faster is a violation. Your rate of rise was greater than 30 feet per second for an extended period so the computer put you into an extended safety stop. The deco/extended safety stop was not for exceeding deco time limits but for the rate of rise violation.

I say it's possible that you went upward too quickly for a minute or so and the computers did not record it in a clear way for viewing by the graph, but it happened for long enough for the computer to calculate you needed the extended safety stop. Even if you swim side-by-side, your profile can still be different, especially with one computer on the hose and the other on a wrist.

Any other ideas? Is this possible? Or probable?

 

[bleeb]

I would suggest that you both incurred the extended safety stop due to a rate of rise violation. Suunto prefers a 'safe' rate of rise of 30 FPS, any faster is a violation. Your rate of rise was greater than 30 feet per second for an extended period so the computer put you into an extended safety stop. The deco/extended safety stop was not for exceeding deco time limits but for the rate of rise violation.

I had wondered a similar thing myself at one point. I *think* any ascent rate violation large enough to extend a stop should be flagged in the data recording, regardless of sample rate. It should then show up (as an exclamation point) if using Dive Manager.

 

[Hatul]

I had wondered a similar thing myself at one point. I *think* any ascent rate violation large enough to extend a stop should be flagged in the data recording, regardless of sample rate. It should then show up (as an exclamation point) if using Dive Manager.

What about the sampling rate as Willar suggested?

 

[bleeb]

What about the sampling rate as Willar suggested?

From looking at the one time I was caught in an roller coaster, logging alerts appears to be independent of sample rate. Events are actually separate records from routine dive data, and the time stamps are odd, off-sample period values. Time stamp resolution appears to be one second.

Actually, looking some more at the detailed profile data for that dive (i.e. not just the graphical presentation), when we hit the beginning of the roller coaster, I see two events with the same time stamp: an ascent rate warning log record, followed by a mandatory stop log record. Only the latter shows up in the graph, and the subsequent ascent warning records are not followed by additional mandatory stop records, presumably because I'd already tripped the flag.

 

[Bubbletrubble]

Willar may be correct about the ascent rate exceeding the recommended rate. This would impose a required mandatory stop. I'm not sure how the computer determines the length of said mandatory stop. For instance, will the mandatory stop lengthen if the ascent rate is exceeded on multiple occasions during a given dive? I do believe that the mandatory stop time would be added on top of an incurred deco obligation.

In my mind, there are a few facts that I found interesting:

• SeahorseDeb stated that that water was extremely choppy and it was difficult to maintain the 15 ft. stop without any visual reference.
• The 10 min. deco stop (at 15 ft.?) requirement imposed by the computer is consistent with a relatively minor deco obligation.
• She exited the water with an unfulfilled deco obligation, but her buddy did not.

I cannot account for the significant difference between when SeahorseDeb's dive computer put her into deco (17 min. into the dive) and when her buddy's computer put him into deco (27 min. into the dive). That's a mystery to me. How close was she to her buddy during the initial phases of the dive? Perhaps she was lower in the water column at certain points. Perhaps she wasn't ascending as quickly as her buddy. Maybe her buddy was managing his ascent in such a way that he was riding the line between low, single-digit NDLs and deco. When the two divers paused at the 82 ft. mark, his dive computer finally reported a deco obligation.

Regardless of how the deco obligation was incurred, it's pretty clear that SeahorseDeb was being bounced around in the water column in the chop. This may have moved her slightly above/below the deco floor (20 ft.?) specified by her computer. For deco obligations, Suunto computers display the minimum ascent time when the depth of the diver is considered optimal, i.e., near the deco ceiling. This is an important point because time spent below the deco floor would not count towards fulfilling the deco requirement. Moreover, if the diver spends the majority of the stop nearer the floor than the ceiling, this would increase the length of the deco obligation beyond the minimum ascent time.

If you read the Suunto Cobra 2 manual carefully, particularly the section regarding deco obligations, the Suunto computer will display a "down" AND "up" arrow (together looks like an hourglass) when the deco stop is being conducted at the optimal depth (near the ceiling). When the diver is still in-between the deco floor and ceiling...but closer to the floor, no arrows will be displayed. In both scenarios, the diver is fulfilling the deco obligation...but one is definitely faster than the other.

I suspect that SeahorseDeb was not at the "optimal" depth for fulfilling her decompression obligation. This, combined with only doing a 4 minute stop in the 15 ft. range, contributed to a violation of the deco obligation and the computer going into "Err" mode.

I don't understand why the OP didn't just prolong her stop at the 15 ft. range. Was gas supply limiting? If not, I would think she could have communicated to her buddy that she needed to get closer to the deco ceiling so that the actual deco obligation would have been closer to the reported minimum ascent time. Alternatively, she could have stayed at her current stop depth (15 - 20 ft.) until the computer cleared her. Obviously, this would have been longer than the reported minimum ascent time of 10 minutes.

Having used Suunto dive computers for many years, I don't mean to imply that the OP narrowly missed getting bent due to her actions. One of my regular buddies uses a more liberal Sherwood Wisdom computer. We have done more "aggressive" dive profiles for which my conservative Suunto will return a deco obligation of 10 minutes at 10 fsw, while his computer will still be in the "yellow" nitrogen loading zone with significant NDL minutes remaining.

Frankly, I think that discussions of sampling rates and the variables (blood flow) being used by various deco algorithms are interesting...but irrelevant with regard to explaining what happened to the OP.

I agree with Hatul that it would be important to rule out depth sensor malfunction by having SeahorseDeb use both computers on the same dive. Perhaps it would be best to attach the Vytec to the Cobra console for more consistent ambient pressure exposure (since we know that wearing a computer on a wrist might place it higher in the water column). Just a thought.

What do you guys think? Am I off-base here?