Suunto Cobra vs. Vytec profile inconsistent

[SeahorseDeb]

Willar and B ubble Trouble I'm directing this response to you two, but others are still pointing out things to consider. I'm going to lay out the dive to you according to my computer printout, hope this helps. I was using air, I'm nitrox certified but just used 21% for this dive. Want to give you some detail though about the dive site. Jump in off a dock, and it's a straight drop to 105 feet. We descend carefully as vis drops at about 50 feet nearing the bottom it is nearly dark. Bottom is extremely silty, rocky slope on one side. Easy to navigate. At 5 minutes into my profile I am at 100 ft. At 7 minutes I am at 104 ft. Max depth. At 12 minutes I am at 80 feet. At 17 minutes I am at 90 feet and deco warning comes on, indicating a 10 minute stop. I noted the warning and continued the dive side-by-side with my buddy ascending to 74 feet at 27 minutes into dive. Then my buddy's deco warning came on. I began a ascent as follows: from 70 feet to ascend to 18 feet I had reached 34 minutes into the dive. I took 7 minutes to ascend 52 feet. After that, my buddy and I tried to hang onto a 15 foot safety stop, but as I indicated, the water was very choppy and it was hard to stay at 15 feet. My buddy and I have been on several dives together, each going gradually deeper to test our buddy skills, practice air share drills, and communication. There isn't much to do here except look at silt or rocks, fish are rare, so skills are our primary dive objective and also practice our trim and bouyancy. My computer is still set at the 30 second sampling rate too. The water wasn't choppy until we were about 15 feet from the surface. My buddy also excited the water with an unfulfilled deco stop, as set forth by the computer. I did notice in this month's "Alert Diver," one of the articles did mention that the same manufacturer of a computer may have a different algorithm. As I mentioned, I have my buddy's computer printout, and when I hold both of them up to the light, it appears as if it were the same profile, we really stuck together on this dive. I do understand the deco floor and ceiling and it showed me cleary that I needed to stay where I was for ten minutes. I have 82 dives on this computer so am very comfortable with it. I'm not going to change the personal settings on it, nor will I willingly ignore them, it just seemed to me that on this dive there was an error, and at the time, I knew it was not a human error. I always wash my gear off with fresh water no matter if I dive fresh or salt. I still have 100% battery too. You make a good point: time spent below the deco floor would not count towards the deco obligation. Quite right. I've understood that we should ideally be at chest-level in the water between the floor and the ceiling. I have vacation coming up, will be diving salt. Don't plan to do diving below 70ft and not likely more than 2 dives a day. I'll be watching this carefully. I may also ask my LDS if they have a wrist mount computer I can borrow. I don't think either of you are off base. Both of you have made very good points which is the reason for the post: to understand why I incurred a deco obligation when I was not in violation. I am a very conservative diver that's why I'm so perplexed by this!!! BTW Willar, I talked to someone at DAN asking them which tissues were being viewed on the sampling rate and was told they are not specific, but we can go back to our basic understanding of fat being slow, spinal cord being fast, etc. Thankyou so very very much for your feedback!!!

 

[hdugan]

Are you using Suunto's SDM to get your profiles? It has a graph that shows tissue loading. If you move through the profile with the mouse you can watch the graph change. It should have 9 bars (Those model suuntos use a 9 compartment alogarithim), the taller the bar the more load in that compartment. Which bar causes the deco? With your profile it should be about the 2nd bar.

 

[Willis]

Howdy - I'm the buddy Deb's talking about here.
Just wanted to clarify, I actually did clear deco obligations, at 33 mins into the dive - 5 minutes after they were incurred. Max ascent time called for was 4 minutes. By the time we got to ~15 ffw it called for 2 minutes - IE a safety stop. I cleared this and then some before surfacing.
Looking at the profile I show the 3rd and 4th bar rising slightly into the red - not sure if that's meaningful here or not.
Also of note is my computer samples at 10 second intervals, not sure if that would make much of a difference either. A majority of the dive was spent without lots of rise or descent.
I did have a rise violation, but only after the computer called for deco. I'd be interested to hear how rate of rise could itself incur a deco obligation?
Some interesting points made to be sure. Would be curious how Suunto may/may not be including SAC rate into algorithms.
It was a great training dive for me, highlighted some things I definitely need work on, and as usual some gear that would make life easier. Had one of us blown a SMB from depth and ascended on the line things could have gone smoother, particularly in the chop.
Would also be interesting to have Deb run the computers in tandem sometime, I just need to pick up a bottom timer as a backup for myself first. Hmm, more gear...

 

[SeahorseDeb]

hdugan yes, I am using SDM program. At 16 inutes, 20 seconds it showed tissue compartments 2 and 3 at 100% and compartment 4 at 99%. I enjoy studying about deco and tissue saturations so it's not strange to me which tissues "might" have registered at 100% but I do not beleive that my computer was accurate. I'm flummoxed. Thanks to my buddy for weighing in on this subject. I'm in a testy area with this problem, however if the rate of ascent was too fast, perhaps the bubbles would have grown larger, and that's why the ascent warning goes off on our computers. Also, I also would wonder how our SAC rate would/could be considered into the algorithm since these are "estimated compartments" according to DAN. As my buddy mentioned, we need more gear. Now for that Galileo wrist mount.......

 

[hdugan]

The ascent rate would effect the Next dives Total No Deco times only, it has no effect on the current dive. As long as the dive we're descussing is the first of a 24 hour period No warning apply.
Suunto Vyper/Cobra types don't measure gas consumption, they store start and end pressure only. SAC is calculated in SDM from the profile data, so that has no bearing on the problem.

I just looked up a similar profile to yours.

2:30 to 97'
102' @ 4:30
106" @ 6:40
100' @ 11:00
90' @ 14:00
85' @ 16:50 up and over a deck
95' @ 17:20
95' @ 20:30 DECO Warning
100' @ 21:30
100' @ 22:30
begin ascent for a 1 min stop @ 40', 1 min @ 30', 2 min @ 20' and 3 min @ 10'

I use a Vytec and for some reason SDM is not telling me what the RGBM setting was. I almost always use 50% however. This was the 25th dive of a week long Keys trip (the 'Duane' IIRC).
The Profile/Deco warn was similar to your buddies.

I think your Gekko had an Error, it acted like it was running an altitude dive or your personal conservation setting was not at P0. Fortunatly, it seems to have errored on the side of conservative.

 

[SeahorseDeb]

I'm thankful it errored on the side of conservative, however next week when I'll be in salt water and doing 2 dives at least over a 5 day period I'll be watching the data carefully. I'm going to write on my slate what the "square" profile would be, just in case! I couldn't figure how the Cobra 2 or the Vyper could measure gas consumption! Thanks!!!

 

[hdugan]

I couldn't figure how the Cobra 2 or the Vyper could measure gas consumption!

The Cobra2 is a very different computer from the Cobra. It is very similar to the D9 as far as software goes. The Vyper2/Air and Cobra2/3s models Do keep pressure data in the profile with each depth sample. I don't think they do anything with it however.