Big Mistake

[Spectre]

Uncle Pug once bubbled...
BTW your SAC for that 15 minutes at 10' was something like .53.

How'd you get that number?

The dive plan description had times 30-42 @ 10, so 12 minutes not 15. I saw your .53 number, and it didn't fit with the numbers that I calculated out on friday. So I re-ran my numbers about 10 times.

What I see is that his Dive was a .73 SAC rate, with .727 working and .742 resting [based on an average dive depth of 49 feet using 2950 psi; and then the resting portion being 12 minutes @ 10 feet with a starting psi of 600 and an ending psi of 150].

 

[CuriousMe]

SeaJay once bubbled...
<snip>
No. My buddy pointed to his bottom timer and did the "open hands" signal, saying to me that we'd hit our turn time. I signaled okay, checked my 'puter, and signaled, "four minutes," if I remember correctly. He signaled back, "okay." I'm sure that his thought process was, "Okay, dude... Your choice. I've got gas." Of course, that's speculation, but that probably wasn't far from the truth.

Not to be overly picky (but after all, that's what a post-mortem on a dive is for though...to find the fault points?). but I think we have different defintions....If my buddy and I are planning on a twelve minute dive....I don't give the turn signal at twelve minutes, I give the thumb. We always turn the dive somewhere in the middle..now I'm not trying to split hairs here....it would just change how I responded to my buddy. I think that as you've already said, the primary mistake was deviating from the plan, but it could have ended right there if you're buddy held you to the plan you both agreed to.

SeaJay once bubbled...
We were centered around the upline, and about a minute later we began our ascent anyway... So the plan wasn't deviated far. Really, my only deviation from the plan was a hesitation of about a minute.

Now forgive me here...I'm not a math wizard (really, no sarcasm here...math's not my strongest point.) But from your account of what happened, you planned on 12 minutes, about 5 minutes into the dive you noticed your comp said that you had 16 minutes (when according to plan you should have had 7), you then started your ascent when your comp said you had 3 minutes NDL. To me that means you stayed down 6 minutes past your dive plan, not inconsequential at 91 feet...it was half again of your original dive plan.

SeaJay once bubbled...
But then I began to ascend very slowly. Too slow, in fact. These two, in combination, were the real deviation from the plan.

My point is that before you tear into me or my buddy, remember that it's not like we dramatically blew off all of our plan... We only deviated slightly. Soooo... Tear into me slightly. Don't overdo it. <snip>

No tearing here, just pointing out unemotional facts, we can't really all learn from this unless we do.

In my opinion though, it wasn't a slight deviation, especially when the fact that your buddy was essentially diving your computer is factored in.

Again, glad that everyone came out of it healthy.

Peace,
Cathie

 

[Big-t-2538]

I have a couple of questions in response to some of your concerns...I'm not trying to be a prick, but take this as you wish....

The 'troll' had 7 points, all of which in my opininon were valid....but you poitned out that #'s 2 & 3 didn't need to be seperate....(plan your dive, and dive your plan). In fact how can these not be 2 different points....I can plan dives all day, but diving them is a totally seperate thing...which is what wasn't done in your case and caused the emergency.

As for planning a dive with your buddy...how can the 2 of you not have the same plan? I don't care who is diving what gas where (so long as their not exceeding MODs) there is one plan per buddy group...

As for the SAC rate thing, like UP said, you don't want to fudge numbers down...you want to fudge them up...I have never had an OOA situation, but I sure as hell don't want to experience it. If I plan too low of a SAC, that just might be the case...

 

[SeaJay]

Uncle Pug once bubbled...

Don't try to fudge the numbers down.

Fudge them up.

Improve your actual rate of consumption but still take plenty of gas.

UP, I didn't miss that point. My "just trying to improve my numbers" comment was in reference to the SAC of .53... I was jokingly referring to the fact that I was nitpicking to see if I could get a lower number as an estimate for that last 15 minutes.

I completely see your point. I think you missed my humor.

 

[Cave Diver]

SeaJay once bubbled...
What about the fact that 400 psi in an empty tank is actually less volume than 400 psi in a full tank?

Let me see... If I remember my math correctly rated volume divided by working pressure = cubic feet per psi

So a 77.4 cft tank with a working pressure of 3000 psi:

77.4 / 3000 = .0258

.0258 cft x 400 psi yields 10.32 cft of air.

Using 400 psi will mean using 10.32 cft of air regardless of whether it is the first 400 psi you use or the last 400 psi...

Am I missing something here???

 

[Uncle Pug]

Spectre once bubbled...
How'd you get that number?

Wading through the posts I found several different sets of figures but the ones I was using were from a post where he simply said he spent 15 min @ 10'.

so:

15 minutes @ 10'
600psi to 400psi
AL80 77.4cf @ 3000

so:

77.4/3000=.0258 cf/psi
10' = 1.3ATA*
600-200=400psi

so:

.0258 *400=10.32/1.3=7.9/15=.529

But I'm not good at math so feel free to correct it.

However when I just looked at the post where he detailed dives one and two I guessed his SAC for dive one at around .5 but his SAC for dive two at around .7

This made me think that perhaps his planning was off because he credited himself with having a better SAC than he consistently has.

But who knows with these kinds of post where they give the information in drips and drabs. Sometimes it is best to step back and just look at the bigger picture rather than get emeshed in the details.

I think that the best thing you can learn from this is to not over estimate yourself.

 

[SeaJay]

Spectre once bubbled...


How'd you get that number?

The dive plan description had times 30-42 @ 10, so 12 minutes not 15. I saw your .53 number, and it didn't fit with the numbers that I calculated out on friday. So I re-ran my numbers about 10 times.

What I see is that his Dive was a .73 SAC rate, with .727 working and .742 resting [based on an average dive depth of 49 feet using 2950 psi; and then the resting portion being 12 minutes @ 10 feet with a starting psi of 600 and an ending psi of 150].

Hmmmm... Spectre, I'm not sure how you got your numbers, but according to my software, which took all of the above into account, I had a SAC rate of .58 for the entire dive... And while it doesn't show me individual rates from one point in the dive to the next (it only shows me overall SAC from beginning to end), I'm confident that I lowered my SAC at the very end of the dive as much as possible.

Either way, .73 is not accurate at all. According to Suunto, my average depth was 53 feet, my starting pressure was 3100 psi, and my ending pressure was 150. Total dive time was 42:40, and max depth was 98 feet. This was the second dive of the day, having started one hour and six minutes after the first one ended. According to Suunto, my average SAC on this dive was .58. Since I was "working" at the bottom, but not during my stop, I believe that my SAC at the stop was probably in the mid 40's or so.

 

[SeaJay]

Uncle Pug once bubbled...

This made me think that perhaps his planning was off because he credited himself with having a better SAC than he consistently has.

I'm getting my numbers from the actual data taken on my past 100 dives or so... My Suunto software's got a place where it tells me average SAC per dive.

 

[Uncle Pug]

SeaJay once bubbled...
Either way, .73 is not accurate at all.

you didn't post the complete print out of your Suunto dive manager log but gave us snippets... from that we did our best to come up with figures... don't come back saying that we are not accurate. Of course we are not accurate... you didn't give us accuracy to work with.

garbage in garbage out dude.

 

[Uncle Pug]

SeaJay once bubbled...


I'm getting my numbers from the actual data taken on my past 100 dives or so... My Suunto software's got a place where it tells me average SAC per dive.

Your average SAC will have a whole range of values above that number and if you use it to plan your gas consumption you will continue to do things like this.

You should plan using your highest SAC. Forget trying score a better average dude.

My average is .46 but I plan .7 working and .5 resting.