Scooter multiple stage gas management

[floridabob]

Ok. I get all the numbers. That was my point. I was trying to understand what you guys are proposing for gas reserve rules. Quite frankly, I find it hard to believe that you would, on a single stage scooter dive, dive only 1300 psi in penetration on an 80. Leaving all back gas for reserve. I gotta call BS on that, first point.

RN, as usual, gets it. We just differ on the approach explanation/understanding, but we are aligned.

I propose that you need your gas plus your buddy's gas at the point of max penetration in reserve. Additional gas would be great...but...

You have to know what it takes to exit, swimming, for your dive. Thats your reserve. Then you address your buddy's.

[floridabob]

Or not

[floridabob]

Sorry, poor joke.

Dive solo.

[Sludge]

Quite frankly, I find it hard to believe that you would, on a single stage scooter dive, dive only 1300 psi in penetration on an 80. Leaving all back gas for reserve. I gotta call BS on that, first point.

I do that all the time.

In Jackson Blue it gets me to p4,000', for a total run time of about an hour. My girlfriend likes me to limit my solo dives to the main line, and under an hour. It makes for a nice dive.

[floridabob]

I, too, do dives like that. I am surprised that, with buddies, people only dive that same dive as a rule.

And my point isnt that it isnt or shouldnt be done just that I am not sure I think most people plan a dive that way in a team. I have seen, with great frequency, divers at Ginnie dive to the Hinkle (or the bypass), with scooters and a stage. Drop the stage and scooters there and then switch to back gas and keep going. However far they go is past what most here are proposing.

To be fair, SAC is a variable that pushes numbers one way or another.

Whatever you guys do or not impacts me very little. And I'm not really concerned about it, just surprised to hear most people say that diving 1300p from an 80 is their normal dive with a scooter with a buddy. And a back up scooter, too, for that matter.

[Sludge]

I've scootered to the Henkel three times, each time with a buddy or two, and each time I breathed a stage only.

In fact, I'd venture a guess that 97 of my last 100 cave dives I haven't breathed backgas.

[floridabob]

Think my point is still being lost. What one diver does/does not isnt my point. In fact, polar opposite. I find it hard to believe MOST people are doing what youre doing as a RULE with buddies and a back up scooter. Which is what they said they were doing.

I'm fine if they are, just wouldnt have thunk it.

For me personally, I like to be in the water. I shoot for a 90 minute run time most dives. Plan gas/location/time around that. I prefer a 120 minute dive even more.

But that's me...If I'm driving 3 hours and $55 in gas then I'm going to be in the water.

[RN]

I don't think most people do that. I think most people don't really understand how to plan scooter dives and if they were to have an issue during the dive would likely be very close to empty when they hit the cavern...if they hit the cavern. One of the things I try to do with my DPV students is a stage dive with back or side gas being reserve gas only. I don't get to do it with all classes since different things dictate different classes, but we at least discuss it every class.

[LiteHedded]

I don't do a lot of ginnie springs/Jackson blue diving where almost anything will work.

My scooter dives are multi stage multi scooter affairs and I don't touch backgas.


Ginnie springs is a different beast.

[DA Aquamaster]

Think my point is still being lost. What one diver does/does not isnt my point. In fact, polar opposite. I find it hard to believe MOST people are doing what youre doing as a RULE with buddies and a back up scooter. Which is what they said they were doing.

I'm fine if they are, just wouldnt have thunk it.

For me personally, I like to be in the water. I shoot for a 90 minute run time most dives. Plan gas/location/time around that. I prefer a 120 minute dive even more.

But that's me...If I'm driving 3 hours and $55 in gas then I'm going to be in the water.

I can see a certain advantage in terms of convenience to the practice of not touchging back gas. For example, with 230 cu ft of primary gas, you could dive 3 stages to half plus 200 (using a total of 100 cu ft of gas for penetration) and then still have the full 230 cu ft of primary gas in reserve, leaving you twice your penetration gas to exit on the scooter in the event you "lost" the gas in all three stages (not likely), or a bit more than three times your penetration gas to exit in the event your scooter dies.

Which is to say that it may or may not be enough reserve for a 3 stage dive, but you would probably not have to worry too much about calculating the actual reserve requirements on a 1 or 2 stage dive, at least at reasonable nitrox depths where the deco obligation from swimming out would not be a major factor.

----

But in general I agree with you. Our purpose in taking a cave DPV course was to extend the area of cave we can explore, in more or less the same manner we've done before. In the near term this means scootering to the points we used to swim to on thirds, and then continue swimming from that point, turning the dive so as to arrive back at the scooter with, at a minimum, the amount of gas needed to swim out. In that regard, if we use a third or half of a stage scootering to that point, the gas left in the stage is just extra reserve on top of the reserve we have already calculated and included in our primary tanks.

Now, we could do the same dive using multiple stages to 1/2 plus 200 and keep all the reserve in back gas, but the reserve would be over kill on what are still fairly short p. dives and we'd end up swimming multiple stages for most of the dive, rather than just during the scooter phase of the dive. It's not a big difference if you scooter the whole dive, but it makes a difference if you swim the middle bits of the dive.

In doing dives where all of it on the trigger just to get more trigger time for Marci, we noted that the dives were pretty short, 45-60 minutes, versus 2 to 2.5 hours for our average swim only dives, given the need to maintain a greater gas reserve in the event of a scooter failure and with resepct to the limits of the battery.