Hold that line boys! How precise should you hold depth?

[Rick Inman]

I like 20' (especially now that I'm on the CCR and "enjoying" the buoyancy properties of lung-less control). The stupid HammerHead forces a 10' stop, but it will go away after staying at 20' for a few years. Computers...

Pete, sounds like you are having a blast! Way to go, man!?!!!!! Sure beats installing tires, huh???????

 

[RJP]

My gut feeling is that 1/2 the resolution of the model is fine (in other words +/-5' for the schedule you posted above).

HOLY CARP! Are you kidding?

+/- 5' = 10' swing. That's the equivalent of going up and down from one stop to the next!

If you need a +/- 5' variance for holding a depth you really should not be deco diving.



EDIT: read through the rest of the thread, and am now hoping you are suggesting a +/- 5' window for where you elect to MAKE the stop, not that you are willing to vary +/- 5' once you are DOING the stop.

 

[Blackwood]

EDIT: read through the rest of the thread, and am now hoping you are suggesting a +/- 5' window for where you elect to MAKE the stop, not that you are willing to vary +/- 5' once you are DOING the stop.

Yah, that's what I meant.

 

[Peter Guy]

HOLY CARP! Are you kidding?

+/- 5' = 10' swing. That's the equivalent of going up and down from one stop to the next!

If you need a +/- 5' variance for holding a depth you really should not be deco diving.

(Serious question here.) Is there any evidence that wondering up and down this depth (+/- 5 feet) is dangerous from a Deco perspective? (Note, I am aware of the issue of being on a line in surge and going up and down significant distances in very short periods of time -- i.e., shaking the soda bottle and THAT is not what I'm talking about. Nor am I talking about PPO2 issues.) If, for example, you are doing your deco along a wall, as long as you do your time and have a general upwards trend, does it really matter that the line is jagged?

 

[RJP]

(Serious question here.) Is there any evidence that wondering up and down this depth (+/- 5 feet) is dangerous from a Deco perspective? (Note, I am aware of the issue of being on a line in surge and going up and down significant distances in very short periods of time -- i.e., shaking the soda bottle and THAT is not what I'm talking about. Nor am I talking about PPO2 issues.) If, for example, you are doing your deco along a wall, as long as you do your time and have a general upwards trend, does it really matter that the line is jagged?

Given how little "evidence" there is (in the strictest "evidence-based medicine" aspect of the term) in deco theory and planning, I'd prefer to keep as many constants as possible since there are so many other "+/-" factors going on. (eg: individual variances in anatomy and physiology, levels of hydration, fitness, metabolism, etc.)

Probably matters less if you're simply "diving your computer" since it will modify your schedule on the fly - though every computer will let you bend yourself. But if you're diving a schedule and are varying some of the stops by as much as 10' you're doing a different dive than the table you cut. So what depths and schedule are you supposed to follow for subsequent stops?

 

[Garth]

I hope everyone has good eyesight. Because if you move your wrist too close to your face you might move up and down a foot (per your computer). Makes me wonder why we don't strap our computers around our necks to keep the monitor constant. whatever you do don't put your hand (which has your computer on it) down by your waist, you'll fail the DIR class. haha. good luck in your classes and your technical diving. i'm just not there yet, not even close

 

[RJP]

whatever you do don't put your hand (which has your computer on it) down by your waist, you'll fail the DIR class.

No, actually you won't.

You see, since you should be HORIZONTAL your whole body would be at the same depth. So your waist won't be DOWN anywhere...

 

[Gilldiver]

(Serious question here.) Is there any evidence that wondering up and down this depth (+/- 5 feet) is dangerous from a Deco perspective? (Note, I am aware of the issue of being on a line in surge and going up and down significant distances in very short periods of time -- i.e., shaking the soda bottle and THAT is not what I'm talking about. Nor am I talking about PPO2 issues.) If, for example, you are doing your deco along a wall, as long as you do your time and have a general upwards trend, does it really matter that the line is jagged?

I am not aware of any studies done on divers bobbing up and down due to surge, swell, and just plain wave action. But I have seen a number of divers with torn shoulder tissues from doing the anchor line yo-yo.

In most cases you can let the line run through your hand, but in conditions where there is a lot of scope and/or current you need to put a tighter lock on the line or you will run up over time. In such cases the jon line works well and can be a real benefit to keep from having a dislocated shoulder, which I know of at least one case, or being bashed into other divers equipment and tanks, which I have seen many times.

The jon line dampens out the oscillations and should even out the deco depth/pressures issues.

So will say, "well I just scooter" or "we drift" etc. but how many divers actually have scooters and what if you are in an area where the boats anchor?

 

[rjack321]

Yah, that's what I meant.

I'm not doing 25ft on 100% O2, but otherwise I generally agree.

 

[Doc Harry]

(Serious question here.) Is there any evidence that wondering up and down this depth (+/- 5 feet) is dangerous from a Deco perspective? ...... Nor am I talking about PPO2 issues.).....

Uh.... it is a ppO2 issue, amongst other issues.

The deco algorithms are based on an ascent profile and deco stops. If you don't follow the algorithm then you might as well make up your own schedule. Deco is Voodoo Magic anyway, I'm not going to make it Double Voodoo Magic by introducing my own untried and untested and unproven schedule into the scenario. If the algorithm says stop at 20 feet for 7 minutes, then that's what I'm doing. Not 25 feet for 7 minutes, not 20 feet for 6 minutes............No, I'm doing 20 feet for 7 minutes.

You want scientific proof? Never going to happen. You'll never be able to design a prospective study in which you intentionally push the limits and intentionally get people bent. A retrospective study would be extremely difficult because it would involve intimate cooperation from all deco divers. And even if you could, how would correct for confounding factors such as obesity, alcohol consumption, dehydration, varying ascent rates, yo-yoing at deco stops, etc? Even then, your n of bent divers would be so small that it would lack statistical significance.

All you can do is follow the algorithm as closely as possible and keep your fingers crossed. Intentionally fudge that algorithm's numbers (+/- 5 feet, etc.) and you're in uncharted waters. I suppose if you were using a computer for deco then your variations are automatically taken into account. But who does their deco based on their computer? I think most people cut tables and dive their plan.