Scooter multiple stage gas management

[DA Aquamaster]

I did the math, and I need the same amount of reserve gas to swim out from 3000ft on a Magnus, UV26, XKx or Gavin.

Obviously he referenced a context other than the fixed distance context in your post, but it's fun to pull people's chains now and then.

In the technically absurd it could even be argued that a diver would actually need a bit more gas doing fixed 3,000' penetration on a Mako or Gavin than a Magnus, as the Magnus gets you to the scene of the max pentration failure (gas or scooter) a lot faster with more remaining gas at the time of the failure.

[LiteHedded]

you can outrun your reserves pretty easily on that thing I would imagine. perhaps just not at ginnie :P

[apitkin]

I did the math, and I need the same amount of reserve gas to swim out from 3000ft on a Magnus, UV26, XKx or Gavin.

Now you're thinking like a rebreather diver. Which is probably the best way to plan for a single scooter failure.

[aainslie]

A minor point, but you need more than 3x the gas in some cases, as your "rock bottom" requirements from back gas to get to the first deco bottle go up as well as the gas to exit.



I did the math, and I need the same amount of reserve gas to swim out from 3000ft on a Magnus, UV26, XKx or Gavin.

Obviously he referenced a context other than the fixed distance context in your post, but it's fun to pull people's chains now and then.

In the technically absurd it could even be argued that a diver would actually need a bit more gas doing fixed 3,000' penetration on a Mako or Gavin than a Magnus, as the Magnus gets you to the scene of the max pentration failure (gas or scooter) a lot faster with more remaining gas at the time of the failure.

Wow.

[RN]

1/2+200 results in using around 33.4 cu ft per stage. Overfilled 104's (3600) hold around 280cu ft So, that leaves us with 33.4*7 = 233.8 cu ft used going in with 7 stages, slightly more than an equal amount is reserved. I'm sure on any dive of this magnitude safety bottles would already be in the cave.

Swimming out just isn't an option in my opinion. There's the fatigue/cramps issue, the deco issue, nutrition/hydration planning for increased workload and time, etc.

Let's assume going into a 240ft deep cave with no flow until you reach the 5000ft mark. On a dpv we can cruise in and out at 150fpm, so we're looking at 33.3 minutes in and 33.3 minutes out, for a 67 minute dive time. Using 20/70/120 deco gases you're looking at 179min of deco on VPM. Now assuming you had to swim out (50fpm), that becomes 100 minutes just to exit, plus 33 minutes to enter, so deco becomes 358 minutes. Consider now that you're looking at 26 minutes of back gas deco up to 120 vs 13, so rock bottom doubles, sac rate is at least 20-40% higher, etc.

Even considering a .5 sac, which is very low for that amount of gear in an emergency, you're going to need 413cu ft of gas to get out plus rock bottom for the 180-120 deco. With a scooter that's 140 using the same SAC rate, and realistically a lower sac rate makes it even greater differential, with half the gas from 180-120 needed. I would say that gas isn't the answer, tow scooter is.

For Ginnie, sure, I'll swim out. For Eagles Nest, Morgan, Cream, etc, I'll take the 2nd scooter.

While this didn't happen on a dive where my primary scooter failed, I did have the 2nd scooter fail. I don't count on it.

And for the record, I'm referring to relatively shallow dives in regards to gas management. Anything that's deep enough to require tons of gas really needs to be done on a rebreather. This way you only need to bring gas to get you out.

[LiteHedded]

While this didn't happen on a dive where my primary scooter failed, I did have the 2nd scooter fail. I don't count on it.

And for the record, I'm referring to relatively shallow dives in regards to gas management. Anything that's deep enough to require tons of gas really needs to be done on a rebreather. This way you only need to bring gas to get you out.

in a buddy team you'd need three scooter failures to start swimming.
on deeper stuff if 'rock bottom' becomes a concern take a deeper bottle. I know i would be blowing off those 'deep stops' if I had an issue without even thinking about it

[donlabbruzzo]

Seems there some consistancy in general terms regarding complex scooter dive reserve gas planning. I must be old school, I always do the dive swimming first, track my gas consumption very closely and then decide just what risk level I'm willing to take when using a scooter(s). I did the math from a few recent dives, albeit in very shallow caves, and I still carry and drop move gas than any of these forumlas would indicate.

Since we're all posting our thoughts, I must assume we're all alive, so whatever our bailout strategy is, it's worked okay up until our most recent dive. The next dive could be different unfortunately.

What's been the real life experience out there, don't we all tend to hold the trigger down too long and have far less run time on the scooters than we calculated in the plan. The drag with doubles, 4, 5, 6 or 7 stages and one back up scooter, even with practice is an enormous drain on the batteries at any speed.

I think I'll stick to knowing exactly how much gas I really need to ge the hell out of Dodge and live to post another day. Diving in more shallow caves as we have in Mexico is also a good idea, which I realize isn't something your Florida guys can do.

[LiteHedded]

Seems there some consistancy in general terms regarding complex scooter dive reserve gas planning. I must be old school, I always do the dive swimming first, track my gas consumption very closely and then decide just what risk level I'm willing to take when using a scooter(s). I did the math from a few recent dives, albeit in very shallow caves, and I still carry and drop move gas than any of these forumlas would indicate.

Since we're all posting our thoughts, I must assume we're all alive, so whatever our bailout strategy is, it's worked okay up until our most recent dive. The next dive could be different unfortunately.

What's been the real life experience out there, don't we all tend to hold the trigger down too long and have far less run time on the scooters than we calculated in the plan. The drag with doubles, 4, 5, 6 or 7 stages and one back up scooter, even with practice is an enormous drain on the batteries at any speed.

I think I'll stick to knowing exactly how much gas I really need to ge the hell out of Dodge and live to post another day. Diving in more shallow caves as we have in Mexico is also a good idea, which I realize isn't something your Florida guys can do.

swimming there first isn't always an option. it goes without saying tracking your burn time under load is critically important

[adam0321]

I once talked with a cave diver that claimed (and he was being serious) he could out swim divers on a uv-26. This was his justification for not planning on extra gas for a scooter failure.

[Dsix36]

I once talked with a cave diver that claimed (and he was being serious) he could out swim divers on a uv-26. This was his justification for not planning on extra gas for a scooter failure.

That diver was full of sheet!