Scooter multiple stage gas management

[phillip1]

Not to hijack the stage thread, what gas management do you prefer on multiple stage scooter dives? and why

[jj1987]

Not to hijack the stage thread, what gas management do you prefer on multiple stage scooter dives? and why

1/2+200, don't touch back gas. This way I can have 7 stages fail and still exit using back gas, or lose all of back gas in a ceiling bump and still exit using stages. Unless it's high flow and not very deep, I prefer to tow a scooter as well, swimming out racks up way more decompression than expected (up to 3x the deco on a deep dive), and often times you'll need more stages to exit than you can comfortably swim anyways.

For high flow caves like Ginnie/Manatee/Jackson Blue with a buddy who I know has practiced towing a diver, I'll use back gas, as I can swim out on equal gas to scooter in. To what degree depends on the buddy, current conditions (esp at JB with changing flow).

[LiteHedded]

backgas in reserve, half plus 200 in stages, one or more tow scooters in nearly all cases.
safeties depending on what the cave is like and what we're doing

[chilldive]

Backgas is not touched - just for reserve. Depending on situation and cave logistics, I will tow a spare scooter - everyone I dive with at that level knows how to properly tow a diver and has practiced it with me.

For a two stage dive, I'll breathe one stage going in and the 2nd coming out - again, never touch backgas.
For a three stage dive, I'll probably breathe one stage down, then drop the empty and one full. I'll proceed on the last stage and dive 1/2 plus 200, then turn dive. Never touch backgas.

Beyond that, I'm probably in a team dive mode doing exploration and there will be safety stages set and possible safety scooter set. Also, other stages to be used will be placed by support divers. Still, never touch backgas.

Nothing wrong with the half plus 200 method on stages, I just prefer the smoothness of breathing a stage down then turning or clipping off the empty, depending on how many stages I'm diving with. All this also assumes I'm never diving solo and I have a buddy who is proficient at sharing gas and towing a diver, and we've practiced it.

[RN]

1/2+200, don't touch back gas. This way I can have 7 stages fail and still exit using back gas, or lose all of back gas in a ceiling bump and still exit using stages.

What size cylinders for back gas are you basing this on? I'm guessing you're assuming the scooter doesn't fail with the 7 stage failure. I'd venture to say if you have 7 stages fail your scooter will also likely fail and back gas will not be enough to get you out from the penetration you made with 7 stages. I always plan enough reserve to swim out regardless of anything else. Even with a tow scooter or buddy with a scooter. They only thing you can depend on is your own propulsion, and for some people even that's not true.

[PfcAJ]

You can't always plan so swim out, your deco gas requirements would be completely absurd, especially on deeper dives. Take a tow scooter and a buddy.

[jj1987]

What size cylinders for back gas are you basing this on? I'm guessing you're assuming the scooter doesn't fail with the 7 stage failure. I'd venture to say if you have 7 stages fail your scooter will also likely fail and back gas will not be enough to get you out from the penetration you made with 7 stages. I always plan enough reserve to swim out regardless of anything else. Even with a tow scooter or buddy with a scooter. They only thing you can depend on is your own propulsion, and for some people even that's not true.

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.

[kensuf]

It depends on the dive. Typically don't touch back gas, and use stages to 1/2+200 as others have suggested. If it's a longer dive (3000'+) or deeper dive (120'+) make sure to carry a spare scooter, and possibly go a little more conservative on the stages. On the exit, breathe stages until they're empty then switch; if a problem happens you can jettison the empty stages while keeping as much gas in reserve.

[aainslie]

Work out your speed on a scooter then work it out swimming. With my Magnus the ratio is approx 3. Then plan gas accordingly.

Having a backup scooter obviously makes this unnecessary. All the other rules of thumb may or may not work.

An interesting aside is, should you plan for scooter failures AND needing a double reserve? If you do, you end up taking an awful lot of gas.

For instance ginnie would require me to have about 240 cu ft available and untouched between the Henkel and the exit. Going back to 5000 feet requires about 400. I happen to have that much on repeat dives (I prestage) but will go lighter than that on a single quick dive.

My advice - do the math ( arithmetic really). Don't trust rules of thumb like " don't touch back gas" this rule will sometimes leave you with too much gas, sometimes too little. If you are in a no flow cave with no backup scooter, have something powerful like a Magnus, and want to have double the gas necessary to exit, you should only use 1/7 of your gas. Yup, it's like being an intro diver all over again!

Most of the posts above do not achieve this.

I suspect one of the problems is, few people have realized that scoots like the Magnus seriously change the game. You need a LOT more reserve gas on a Magnus than on a uv26 or Gavin.

DO THE MATH!!!!!

[jj1987]

Work out your speed on a scooter then work it out swimming. With my Magnus the ratio is approx 3. Then plan gas accordingly.

Having a backup scooter obviously makes this unnecessary.

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 suspect one of the problems is, few people have realized that scoots like the Magnus seriously change the game. You need a LOT more reserve gas on a Magnus than on a uv26 or Gavin.

DO THE MATH!!!!!

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.