Northwest Dive Club

loanwolf wrote: Matt
yes it does, if you have a oh shit moment and your air consumption goes up an alarm will sound and it will be telling you your consumption rate is high and changes the gas time at the moment and starts to penalize you with more deco unless you calm down and lower your breathing rate.

I've had a hard time understanding this. BTW this feature was one of the reasons I originally bought my AI Vytec.

The way I understand it the computer gives you air time calculations based on your current breathing rate. So the computer thinks you're fine until you hit that oh S**t moment when you had just enough air time left to get you to the surface/ deco bottle under the previous conditions at wich point it says oops, based on the fact that you're now half panicked at 130 ft and just donated to your buddy who went OOA you now don't have enough gas to make it. It's the dynamic part of this that concerns me. Maybe your computer uses some kind of algrythm to account for this (I'm pretty sure mine doesn't), if so I'd love to know how it works.

OTOH maybe I'm just not understanding the process by which the computer determines how much time you have left.

my transmitters point towards the tank as well. There is no instance where any of my transmitters are pointed "out" where they'd get sheared off. Whether on doubles, monkey, sidemount or the breather.

as lynne mentions, there are a plethora of other things to get line/kelp/etc... tangled around.

LCF wrote:The way Peter has his transmitter mounted on his doubles, it's pointed straight down at the manifold. It would take something very strange to hit it. I really don't think it presents any more of a leak hazard than a port plug, and it would take something very convoluted to get entangled around it -- your first stages are more of a hazard than it is.

Which is not to say I think they're desirable. Note that I never bought one, when the Vytec was MY computer. But I don't think you're inevitably going to die if you use one, either.

Now, when it comes to the Cobra . . . Well, I'm with Scott.

loanwolf wrote: it will be telling you your consumption rate is high and changes the gas time at the moment and starts to penalize you with more deco unless you calm down and lower your breathing rate.

This is anotherone I don't understand. What does your breathing rate have to do with your deco obligation?

depending on your algorithm (on the uemis its a ZHL 8+), if it's adaptive, when your consumption goes up, your deco will go up as well. the uemis takes this into account when figuring how much gas you need to get to the surface considering added deco due to consumption AND the increased consumption itself.

increased consumption implies heavier workload, heavier workload implies more ingassing... more ingassing implies more deco...

Mattleycrue76 wrote:

loanwolf wrote: Matt
yes it does, if you have a oh shit moment and your air consumption goes up an alarm will sound and it will be telling you your consumption rate is high and changes the gas time at the moment and starts to penalize you with more deco unless you calm down and lower your breathing rate.

I've had a hard time understanding this. BTW this feature was one of the reasons I originally bought my AI Vytec.

The way I understand it the computer gives you air time calculations based on your current breathing rate. So the computer thinks you're fine until you hit that oh S**t moment when you had just enough air time left to get you to the surface/ deco bottle under the previous conditions at wich point it says oops, based on the fact that you're now half panicked at 130 ft and just donated to your buddy who went OOA you now don't have enough gas to make it. It's the dynamic part of this that concerns me. Maybe your computer uses some kind of algrythm to account for this (I'm pretty sure mine doesn't), if so I'd love to know how it works.

OTOH maybe I'm just not understanding the process by which the computer determines how much time you have left.

ljjames wrote:depending on your algorithm (on the uemis its a ZHL 8+), if it's adaptive, when your consumption goes up, your deco will go up as well. the uemis takes this into account when figuring how much gas you need to get to the surface considering added deco due to consumption AND the increased consumption itself.

increased consumption implies heavier workload, heavier workload implies more ingassing... more ingassing implies more deco...

So then, when planning a tech dive wouldn't a person with a 0.3 RMV use a different set of tables than a person with a 0.7 RMV?

Also how does the computer predict at what point in the dive and by how much the air consumption will spike (in an emergency) in order to set aside enough gas for that situation.

Just telling me that my remaining air time is now less than it was before is of little help if I don't have enough gas left to get me (and maybe my buddy) to the surface/deco bottle.

Mattleycrue76 wrote:

ljjames wrote:depending on your algorithm (on the uemis its a ZHL 8+), if it's adaptive, when your consumption goes up, your deco will go up as well. the uemis takes this into account when figuring how much gas you need to get to the surface considering added deco due to consumption AND the increased consumption itself.

increased consumption implies heavier workload, heavier workload implies more ingassing... more ingassing implies more deco...

So then, when planning a tech dive wouldn't a person with a 0.3 RMV use a different set of tables than a person with a 0.7 RMV?

Yep.

Mattleycrue76 wrote:Also how does the computer predict at what point in the dive and by how much the air consumption will spike (in an emergency) in order to set aside enough gas for that situation.

Just telling me that my remaining air time is now less than it was before is of little help if I don't have enough gas left to get me (and maybe my buddy) to the surface/deco bottle.

ALL tech instruction is all about learning how NOT to end up in a situation like that. If you let your computer kill you, you're a fool.

i'm not 100% sure on that one. I think it would have to do with other variables including the surface area they have available for gas exchange, how fit they are (as in, is their higher RMV due to lack of fitness or are they just a bigger human, etc..) I know that some people say "lung size doesn't matter", but seriously, how many tiny women do you see outbreathing their big huge 6'6" dive buddy? if i breath at a similar rate as my supersized counterpart and my lungs are tiny, my consumption rate will be different, but he has higher surface area inside his lungs to in-gas off-gas. this one is better left to people much smarter than me to answer

but, back to the computer, the adaptive algorithms are basing it on an increased work load, above what you set as 'avg'. it is constantly calculating, so if your consumption skyrockets, it will calculate according to your rate at that given moment. it can't predict anything, it's basing it on hard numbers.

again, what it is telling you is simply a number based on what it has calculated you need for decompression (constantly being updated) and if you have set a 'reserve' (to be on the surface with pressure) how much time you have before you need to start your ascent taking into account deco and ascent time to make it to the surface with the amount of gas you asked it to calculate these numbers around.

if you think you'll need 2000 psi to get you and your buddy home from worst case scenario, then you tell the computer to warn you as you approach the psi that will allow that... Yes, it will mess things up bit if all of a sudden your consumption rate doubles (if your buddy is sucking down you gas), it's only as good as the data it's getting. by then you are not gonna be worrying about how many minutes the computer is saying you have, you are gonna be running for home... it will still calculate deco for you, ya, it may not be exactly correct, but it will be more conservative if anything.

Mattleycrue76 wrote:

ljjames wrote:depending on your algorithm (on the uemis its a ZHL 8+), if it's adaptive, when your consumption goes up, your deco will go up as well. the uemis takes this into account when figuring how much gas you need to get to the surface considering added deco due to consumption AND the increased consumption itself.

increased consumption implies heavier workload, heavier workload implies more ingassing... more ingassing implies more deco...

So then, when planning a tech dive wouldn't a person with a 0.3 RMV use a different set of tables than a person with a 0.7 RMV?

Also how does the computer predict at what point in the dive and by how much the air consumption will spike (in an emergency) in order to set aside enough gas for that situation.

Just telling me that my remaining air time is now less than it was before is of little help if I don't have enough gas left to get me (and maybe my buddy) to the surface/deco bottle.

I would just set the reserve gas on my umeis as the rock bottom value for me and my buddy at planned depth, that should take care of it.. unless I'm missing something?

ljjames wrote:depending on your algorithm (on the uemis its a ZHL 8+), if it's adaptive, when your consumption goes up, your deco will go up as well. the uemis takes this into account when figuring how much gas you need to get to the surface considering added deco due to consumption AND the increased consumption itself.

increased consumption implies heavier workload, heavier workload implies more ingassing... more ingassing implies more deco...

I have no idea what UEMIS has done in that box, but Bulhmann (ZHL 16 or midget versions with fewer compartments) doesn't care what your gas consumption is. In Buhlmann, higher consumption (just naturally or from a greater workload) does not = more deco. The ratio of inerts, O2, and the ambient pressure they are breathed at are the only real variables. While workload either on the bottom phase or during deco is a medically known minor component, I'd like to see the actual math on how this is intergrated into Buhlmann by UEMIS.

I don't have exact numbers but i do have a simple slideshow on the ZHL 8+ distributed by UEMIS that explains how the adaptive algorithm (the + part) works.

from the slideshow:

Adaptive Algorithm compensates for:

effort of the diver
skin cooling
local changes due to microbubbles present in tissues
changes in gas exchange due to microbubbles present in lungs

this is done by:

adapting tissue half time (saturation speed)
supersaturation tolerance
right to left shunt in real time

(this is not counting the deep stops and safety margins ---> next slide please)

CaptnJack wrote:

ljjames wrote:depending on your algorithm (on the uemis its a ZHL 8+), if it's adaptive, when your consumption goes up, your deco will go up as well. the uemis takes this into account when figuring how much gas you need to get to the surface considering added deco due to consumption AND the increased consumption itself.

increased consumption implies heavier workload, heavier workload implies more ingassing... more ingassing implies more deco...

I have no idea what UEMIS has done in that box, but Bulhmann (ZHL 16 or midget versions with fewer compartments) doesn't care what your gas consumption is. In Buhlmann, higher consumption (just naturally or from a greater workload) does not = more deco. The ratio of inerts, O2, and the ambient pressure they are breathed at are the only real variables. While workload either on the bottom phase or during deco is a medically known minor component, I'd like to see the actual math on how this is intergrated into Buhlmann by UEMIS.

There IS evidence that exertion at depth increases nitrogen absorption. This makes some kind of sense, because the muscles you use will request and receive additional blood flow, and therefore potentially absorb more nitrogen. That's why we're told that dives which are strenuous need to be worked on the tables as though they are 10 feet deeper.

On the other hand, baseline SAC rate has a lot to do with size and muscle mass. I'm almost half the size of my primary dive buddy; he is NEVER going to be able to breathe the way I do. But I can't carry all our gear down the hill at Flagpole, and back up, either. Exertion is calculated by deviation from one's own baseline gas consumption, not by comparison.

LCF wrote:There IS evidence that exertion at depth increases nitrogen absorption. This makes some kind of sense, because the muscles you use will request and receive additional blood flow, and therefore potentially absorb more nitrogen. That's why we're told that dives which are strenuous need to be worked on the tables as though they are 10 feet deeper.

On the other hand, baseline SAC rate has a lot to do with size and muscle mass. I'm almost half the size of my primary dive buddy; he is NEVER going to be able to breathe the way I do. But I can't carry all our gear down the hill at Flagpole, and back up, either. Exertion is calculated by deviation from one's own baseline gas consumption, not by comparison.

For sure, just like mild exercise increases offgassing. But Buhlmann no do workload. There must be some supplemental algorithm running on top, i.e. ala proportionally bumping up the conservatism in VPM. Not really being much into "trusting" computers without a decent grasp of what's behind it all. At the very least, I would personally shut off the UEMIS workload bits (temp compensation as well) until I knew what it was doing and how it was implemented.

richard and lynne, i'm emailing you guys the simple decompression presentation that UEMIS gives to us to run through at seminars and presentations...

you "shut off" the workload by not using the air integration...

Meh. It's all witchcraft, voodoo, and santaria, mixed up with a healthy dose of statistics and actuarial tables. I just leave a white candle burning on top of a white bible while I'm underwater, and if anything hurts when I get out, I rub a magic chicken bone on it until it feels better.

That said, Buhlman seems to work OK for me. I play around with Gradient factors a bit. And whatever vplanner does is pretty good too. I just add time to my shallow stops if I think I might have gotten too cold from a suit leak, or went to 6x my normal sac rate for a minute when I was working too hard or thought I was gonna die. I just don't think about decompression algorithms very much. It's like string theory, as far as I'm concerned. They're both obscure, arcane fields of knowledge understood by very few people. In the mean time, I try to keep my dives in that fat area of the bell curve, where the fewest amount of divers get bent.

where's the like like like button!

nicely said

Yes, great post, Josh. Since nobody really knows what's going on inside us, the little fancy tweaks probably aren't worth much. The middle of the bell-shaped curve is the place to be.

LCF wrote:Yes, great post, Josh. Since nobody really knows what's going on inside us, the little fancy tweaks probably aren't worth much. The middle of the bell-shaped curve is the place to be.

Yes, and you can't triple stamp a double stamp let alone account for all the CO2 generated during the o'snap moment....

Mongo wrote:

LCF wrote:Yes, great post, Josh. Since nobody really knows what's going on inside us, the little fancy tweaks probably aren't worth much. The middle of the bell-shaped curve is the place to be.

Yes, and you can't triple stamp a double stamp let alone account for all the CO2 generated during the o'snap moment....

This thread's almost a year old.....and I don't get the point you're trying to make.....

Yeah, I don't know either. {sigh} It the result of an iphone, the Tap-Talk app and alcohol.

drinking and Tap-Talking.... is that legal?