Computers & DIR

[Scuba_Steve]

Of course. But following that logic, how far can you take this? Does 5 mins at 130 followed by <g> 5 mins at 10 equal 10 mins at 70??

LOL Yeah I find myself and my buddies regularly doing a profile like that

I would suggest the next step after that profile would be ending the dive at minute 22 or so anyway, and not worrying about much else. (Ascent time noted)

We usually follow that dive up after a 10min SI and do a quickie 200ft for 5 minutes and another 5min at 10ft.....

Just havin' some fun, bein' a miscreant and all

 

[doole]

Right. <Slapping forehead>

Would that be the only factor?

 

[Soggy]

Use some common sense. There are situations where depth averaging works, and situations where it has to be tweaked. Engaging your brain a little bit will do wonders. Your 10 mins @ 130' followed by 10 mins @ 5' example is not 20 mins @ 70', it's 10 minutes at 130' followed by deco stops, followed by an ascent to the surface.

 

[lamont]

For everyone preaching tables an BT, how many of you folks out there use VPM B ? those who say I, what is wrong with the VPM B VR3? the argument of "it puts in rediculous stops my tables are better" is out the window.

I've tried running that maximum decompression example on the WKPP website through v-planner (VPM/B) and I get roughly 2x the deco no matter how I futz with it. So, on the far end of the scale, a computer still doesn't work. It also still doesn't allow you to tweak your deco by moving minutes around at stops and trying different strategies, like lengthening high ppO2 stops and shortening low ppO2 ones.

 

[lamont]

Of course. But following that logic, how far can you take this? Does 5 mins at 130 followed by <g> 5 mins at 10 equal 10 mins at 70??

No.

If you notice on the examples I posted of how I do it, you can't do it with a reverse profile. You also need to have roughly similar depths.

If you want a technical discussion of how I think about it, the steep part of the exponential curve is nearly linear and the steepness is roughly proportional to the difference in depth. So what I'm doing is adjusting for the increased gas loading in the beginning of the dive while deep by increasing the depth that I wind up at and then using the table value there.

On the example where the 60 foot stop is extended coming up from ~100 fsw, I don't use depth averaging. I mentally take the controlling compartment at 60 feet and load it at 2x the rate for time spent around 100 fsw and then add the time at 60 fsw and compare against the NDLs. This is sufficiently conservative that I ignore details that the computer would take into account like that the controlling compartment will be a little bit faster, etc.

I don't suggest trying to do this kind of mental arithmetic approach to recreational diving if you aren't familiar with the models and can't make decisions about where the approximations apply and when they don't. I've taken so many college level math and physics courses that I find it intuitively obvious where approximations are valid and where they are not. If its not obvious to you that 5@130 + 5@10 != 10@70 then this isn't for you.

Also, at a minimum I do 1 min stops from 1/2 max depth to the surface, and usually throw in at least 3@ 20, 3@10, or sometimes up to 15 mins coming up from 30 checking out stuff at shallow depths and practicing hovering or other drills. Any small mistakes I make in the NDL which results in a small deco ceiling will get fixed there.

 

[FIXXERVI6]

I've tried running that maximum decompression example on the WKPP website through v-planner (VPM/B) and I get roughly 2x the deco no matter how I futz with it. So, on the far end of the scale, a computer still doesn't work. It also still doesn't allow you to tweak your deco by moving minutes around at stops and trying different strategies, like lengthening high ppO2 stops and shortening low ppO2 ones.

WKPP forces bubble growth on purpose to get out of the water faster, there is no dive computer / program on the planet ever created or that will ever be created that does this, and there is NO way in hell I'd force bubble growth on the shallow stops just to get out of the water faster, and the other thing is I doubt there are any people on scuba board that performs dives of this level so I dont' see how it really applies, the VR3 wasnt' designed to break records on getting people out of the water, its meant to get you out of the water alive and as clean as possible in balance with getting out in reasonable time.

How does a computer not work? If I follow VPM/B and stay in the water 2X longer tan GI did and get out alive, that means it did not work?

I have messed with v-planner and tweaking the profile by putting in deep stops as a level for like 1 to 3 minutes to see how it reacts, sometimes it gets trippy other times it will do what I expect.

If I stay in the water 15 minutes longer than someone else on the same profile that means the computer did not work?

My only argument I can see as being valid against computers is people will turn their brains off, if their computer blows then they are in deep do do, anyone doing deco in my opinion should be able to fudge some deco curve based on understanding of deco theory, if their computer blows and they can't fudge at all, then yea the computer was real bad for that person.

 

[RTodd]

Fascinating thread, you bunch of miscreants.

I've been using a computer for years but never stopped doing post mortems on dives with the tables, a drill I highly recommend for rec divers on computers. You begin to understand how aggressive computers can be.

Be that as it may, the averaging deal you guys speak of has got my head reeling a bit. Can you really say that 10 mins at 40 plus 10 mins at 100 is equivalent to 20 mins at 70?

The only way you can make a computer "agressive" is to dive ridiculous profiles from a decompression standpoint that the computer does not understand and therefore won't heavily penalize you for. Multiple bounce spearfishing dives with older computers is a great example. And, those of us that aren't using computers don't dive that way anyway. In all other circumstances, every computer out there is more conservative than what many of us can do safely in our heads.

Personally, I don't use depth averaging and most of the other tricks explicitly for recreational "no deco" dives. Because a lot of our recreational profiles tend to force us to push the limits on surface interval, I carry a couple of buhluman based multi-level, multi-dive profiles that I have created that basically serve as a reminder of where the model limits are with the few general profiles I would ever dive. The "all in your head" tricks are harder for me to use with very short surface intervals. Granted, short surface intervals aren't a good idea but are sometimes dictated by logistics. And, using a table does not give me enough control over what I want to see from the models. I use depth averaging and other stuff to modify my ascent strategy for each particular dive based on the surface interval (pre & post dive) and actual profile.

Like a lot of things, until you have started really paying attention to your profile and experminenting with this stuff, what I just said won't make much sense.

 

[boomx5]

and the other thing is I doubt there are any people on scuba board that performs dives of this level so I dont' see how it really applies, the VR3 wasnt' designed to break records on getting people out of the water, its meant to get you out of the water alive and as clean as possible in balance with getting out in reasonable time.

Actually there are people here that do dives like that. Regardless, one of my good friends was diving with a guy a few weeks ago who was using a VR3. He told me that after a 240' dive the VR3 was calling for 30 minutes more deco than the standard Ratio Deco profile they ended up doing.

 

[FIXXERVI6]

Actually there are people here that do dives like that. Regardless, one of my good friends was diving with a guy a few weeks ago who was using a VR3. He told me that after a 240' dive the VR3 was calling for 30 minutes more deco than the standard Ratio Deco profile they ended up doing.

I'd be curious what difference the VPM/B version would have had, no matter what tho I suspect computers will always require more deco.

 

[RTodd]

WKPP forces bubble growth on purpose to get out of the water faster, there is no dive computer / program on the planet ever created or that will ever be created that does this,

Uhm, if the profiles were designed to force bubble growth a lot more team members would have been pretzeled or killed. That is not what WKPP deco methods do at all. They actually minimize bubble growth. More conventional profiles cause more bubble growth. The longer stop times of these strategies help treat that. Weinke is the anti-bubble master and he generated a lot of the profiles the team used in the earlier days since it was one of the few groups willing to actually dive his stuff.

Part of where you are confused is that the team does rely on people in very good shape who can get away with microbubble offgassing after the final stops. But, most commercial and military deco diving operations do the same thing by simply washing out the people that can't handle that. Most deco dives invovle microbubbles anyway. It is just a matter of being able to handle it. If you do not have PFO type issues and are in great cardio shape, this is just another way of accelerating deco. If you do have these issues, you will eventually get badly whacked no matter how long you stay in the water.

If someone that can actually explain this stuff better cares to jump in here, that would be great because I have just glossed over huge amounts of relevant info.