DPV Diver

[floridabob]

I can appreciate your rationale. Do I like to scooter, yeah it can be fun,just like I enjoy taking my motorcycle for a spin. Since a majority of my diving is research based, and looking at species, carrying an oversized food processor blades near imperiled species is a little counter intuitive.

Laugh out loud.

Yet again.

I excitedly await yet another post......

[Nitrogenius]

I think you're forgetting that you can take two scooters instead of one for dives where swimming out becomes impractical.

Well there is a lot of opinion out there that also with a backup scooter you should have Rock Bottom Gas to make it out swimming..

[nakatomi]

IIts easy to swim out from the Hinkle on an 80. Same in JB on the aforementioned dives.

Well that may work for you, not so much for me. Let's try the math

Assuming one should swim back to the exit at 50 feet/minute from 4000' (the JB example) and at an average pressure of 3.7 ATM. A sac rate of 0.4 may be a little optimistic considering one would be on the clock, but let's just assume...
So, it's 4000 / 50 = 80 minutes of swimming. Let's say you're fast and can even do it in 60 minutes and still maintain the sac rate of 0.4, which is pretty much not going to happen.
Anyway, that would be 60 x 0.4 x 3.7 = 88.8 cuft of gas.
So Edd would need to recover a dead body about 8.8cuft short of the cavern, right around the first breakdown?

Remember, this started about "would you do it again, is it worth it, and why" rather than a look at me.

The example on how to plan a dive was just that, an example. Please provide better examples, I'd love to learn how to plan safely and yet get to see more.

[midway]

You are correct, it is comparing apples to oranges. Both dive plans are very different. DPV diving requires different planning than swim diving, which is why the class is so helpful. ...

Understood. I was just trying to relate the gas calculations to Frank's original question to floridabob. Since he's not directly answering the question, here's my take which provides a rough estimate:

With a DPV you get to dive further, safely (even applying the same 1/3 rule as swimming), but the additional distance depends primarily on one's RMV swimming and the speed of the scooter. There's even a formula one can arrive at.

Simplifying assumption: assume constant depth and suppose that using x cubic feet of gas (cf) you can swim a distance of a * x feet. Obviously there may be nonlinearities but this is just a first-order approximation. Constant a depends on RMV for the cave in question.

Suppose when scootering you can travel a distance of b * x feet where b > a. b depends on DPV speed and how inefficient a swimmer is.

Applying the same conservativeness factor 1/3 (it can be easily generalized to DPV planning as noted by Oliver) and assuming L is the total gas volume available (ignoring deco planning), the distance penetrated using DPV is b * x and we want at the turnaround gas volume to have enough has to swim twice the distance penetrated (the standard 1/3 rule). This means solving

a * (L - x) = 2 * b * x

which yields x = a * L / (2 * b + a). If b = a (for example, we're not using DPV), then x = L / 3 which is the standard 1/3 rule.

To estimate how much further we can penetrate using a DPV, we divide the distance reached by scootering by the distance gotten from swimming:

b * [a * L / (2 * b + a)] / [a * L / 3] = 3 * b / (2 * b + a)

If b = a, then the ratio is 1 as it should. When b > a, then the quantity is upper bounded by 1.5. Hence even if your DPV is super fast and your RMV lousy when swimming, you can't expect to penetrate 50% more with a DPV compared to swimming. As Oliver noted, when applying more relaxed gas planning for DPV dives, the distance can be further increased. But the more north of 50% one goes, the more one may be pushing it. The above is in the case of solo diving and a single DPV.

[floridabob]

Edit....

I had a great post then discovered Gag Season runs till Dec 3. Much better use of my time.

bob

[nakatomi]

With a DPV you get to dive further, safely (even applying the same 1/3 rule as swimming), but the additional distance depends primarily on one's RMV swimming and the speed of the scooter.

Yes, you nailed it and that is the core of it. A super fast scooter and an incredibly low SAC rate (swimming) will enable a diver to penetrate the farthest.
A slow scooter will obviously not provide as much benefit and a high SAC rate will be a further issue, which of course can be compensated to some extent with more gas to begin with.

[Nitrogenius]

...which of course can be compensated to some extent with more gas to begin with.

Well but then with more gas you can simply swim farther as well being my initial point..
The scooter just makes it easier to drag all that gas into the cave
The other thing is I guess how honest one is to himself planning on SAC rates and swimming speeds and their combination..


Seems to be a bit similar issue as to Breather Bailout planning creating quite a spread between what some people think they can make it out and a sound and safe planning..


I ve seen folks thinking 2 40s is gonna do anything at 330feet dives.. Well after having myself experiencing my SAC rate to skyrocket after a mild (!) CO2 hit, I do think way different..


With the aftermath I had a SAC of 2.5 cft/min for full 3 min.. Then dropping to 1.4 for 15 min or so until stabilizing to normal levels..

[jj1987]

Well but then with more gas you can simply swim farther as well being my initial point..
The scooter just makes it easier to drag all that gas into the cave
The other thing is I guess how honest one is to himself planning on SAC rates and swimming speeds and their combination..


Seems to be a bit similar issue as to Breather Bailout planning creating quite a spread between what some people think they can make it out and a sound and safe planning..


I ve seen folks thinking 2 40s is gonna do anything at 330feet dives.. Well after having myself experiencing my SAC rate to skyrocket after a mild (!) CO2 hit, I do think way different..


With the aftermath I had a SAC of 2.5 cft/min for full 3 min.. Then dropping to 1.4 for 15 min or so until stabilizing to normal levels..

There is no way that you'll ever be able to swim as much gas as you can scooter with.

[midway]

A super fast scooter and an incredibly low SAC rate (swimming) will enable a diver to penetrate the farthest.

It's the opposite. That is, assuming your swimming efficiency is lousy -- high SAC rate -- but when scootering it improves significantly (low SAC rate), then, with a fast DPV, you can go much farther safely relative to swimming (not using a DPV). It's not difficult but not necessarily intuitive.

Two recent DPV related incidences, one at Ginnie resulting in fatality and the other at JB where the diver was saved by stage bottles (and Edd finding the diver and scootering out together) that you and Rob had deposited, if I'm not mistaken, are both out-of-gas situations (as opposed to heart attack etc.). Based on some of the discussion I've seen thus far, just wondering if there is not as clear cut rule for DPV planning that, perhaps, is contributing divers to push the envelop unknowingly.

[rddvet]

Iand the other at JB where the diver was saved by stage bottles (and Edd finding the diver and scootering out together) that you and Rob had deposited, if I'm not mistaken, are both out-of-gas situations (as opposed to heart attack etc.). Based on some of the discussion I've seen thus far, just wondering if there is not as clear cut rule for DPV planning that, perhaps, is contributing divers to push the envelop unknowingly.

I definitely don't believe the story you've heard about that incident at JB is accurate. I won't share what I know as its not my place, but I can say I can reliably say its different.