T2T forum entrance requirements change

[sskasser]

sweet! looks like compusa has a bunch in stock. I'm gonna run over there after work

I hate that place. I always buy more stuff than intended. Almost as bad as Skycraft

 

[LiteHedded]

hey I got one! 10 bucks!
here's a cave dive we did on Sunday. I don't remember that big hill being quite so big lol

 

[PfcAJ]

And the week before

 

[TSandM]

You know, I look at pretty violently sawtoothed profiles like that and wonder -- there's a lot of opportunity there for bubble-pumping, and I don't think anybody's idea of depth-averaging validity extends to profiles that are swinging repeatedly between 5 ATA and 3; what ARE you guys doing for decompression planning?

 

[TSandM]

You know, I look at pretty violently sawtoothed profiles like that and wonder -- there's a lot of opportunity there for bubble-pumping, and I don't think anybody's idea of depth-averaging validity extends to profiles that are swinging repeatedly between 5 ATA and 3; what ARE you guys doing for decompression planning?

 

[LiteHedded]

You know, I look at pretty violently sawtoothed profiles like that and wonder -- there's a lot of opportunity there for bubble-pumping, and I don't think anybody's idea of depth-averaging validity extends to profiles that are swinging repeatedly between 5 ATA and 3; what ARE you guys doing for decompression planning?

just straight average depth for the most part. we do a little tweaking and nice long ascents from 20'

you should see the one from my last dive at manatee. that is some sawtoothing for sure

 

[PfcAJ]

You should see the Manatee graph. Its nutty.

I don't recommend this, but we deco based on the actual average with vpm+2 (modified for an S-curve) and call it good. Gas breaks are counted as total time. We typically take a ~20min surface deco, drink before, during, and after the dive, and try do a pretty slow ascent. Its been working so far

 

[lamont]

You know, I look at pretty violently sawtoothed profiles like that and wonder -- there's a lot of opportunity there for bubble-pumping, and I don't think anybody's idea of depth-averaging validity extends to profiles that are swinging repeatedly between 5 ATA and 3; what ARE you guys doing for decompression planning?

well taking 110 fsw as more of an "average max depth" since the excursions below that were minor, and i'm assuming 21/35:

4.3333 ATA * (1 - 0.21) = 3.423 ATA = 79 fsw

so you can swing between saturated at 110 and 80 feet without involving more than boyle's law expansion of microbubbles, you don't drive a gradient at all. the gradient that they were driving at 60 was probably 20% or less of the bulhmann limits in a fast compartment (blood) which circulated through the lungs and got cleaned up. then they went back down and recompressed. coming off the last excursion to 130 it looks like they did some deep stops and then they did a pile of time at 70 which again is going to clean up any fizzy mess in the fast compartments (and eyeballing it, it kinda looks like it might have been a little longer than necessary, YMMV, but i'm guessing they switched to 50% and drove a high ppO2 for awhile which can't hurt with any fizz). then after that, deco'ing the moderate-to-slow compartments using depth averaging makes total sense.

(oh I'm looking at PfcAJ's profile).

sawtooth near the bottom isn't as much of an issue as sawtooth with a larger driving gradient. if they were going down to 150 and then hitting 20 feet, that'd be crazy. i remember nick touissant posted some crazy profiles on gavinscooters which were worse than that and he talked about scootering through the shallow sections and being able to feel the bubbles in his legs or something....

 

[LiteHedded]

18/45 in both

 

[TSandM]

I remember reading a couple of Brian Kakuk's descriptions of his exploration dives, where he does a segment at 150, and then up to about 35 feet, and then back for a long segment at 150 -- not really a very healthy kind of profile, but if it's what the cave does, what can you do?

(Of course, my instructors would have me deco out the deep sections on the ascent to the shallows EACH time.)