OP
Stages: 1/2+200 or 1/3rds
- Thread starter rjack321
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LiteHedded
Contributor
I dunno man.
seems like a good way for the reg to come out of the donees mouth. it sounds like an idea that might work better in open water than in a cave.
seems like a good way for the reg to come out of the donees mouth. it sounds like an idea that might work better in open water than in a cave.
SuPrBuGmAn
Contributor
...and if the cave doesn't allow side-by-side scootering. Some may be fine for single file, but not-so-viable side-by-side.
If you HAVE to set a standard, I'd think single file towing would be it...
... however, I can see where side-by-side could be easier to maintain contact and I wouldn't rule it out(granted, I'm admittedly very inexperienced with scooters and at this point, would simply rather swim).
IMO, the situation and site should have some dictation on methodology
There is no ONE way.
LiteHedded
Contributor
I can't imagine coming out of any of the popular scooter caves in that configuration.
difficult at best and complete and total charley foxtrottery at worst
difficult at best and complete and total charley foxtrottery at worst
PfcAJ
Contributor
Ya, scootering side by side while sharing gas is charlie-foxtrottery. You've got so speed match scooters, turning (ie dodging cave structures) must be timed precisely or you're going to lose it, the touch contact will be broken as soon as someone needs to add gas to their DS or wing (oral or by the inflator). Getting into a regular towing position lets one person do the driving. Plus, it puts your other scooter out of the way, so it can't pick up rocks/line or otherwise break (not as easily, I should say).
While most anything will work in shallow caves, things change when deeper. 1000psi in ginnie does not equal 1000psi in Eagles Nest. An entire stage will last a staggering 17 minutes at 280ft (.5 sac rate), and if you think you have a .5 when things are REALLY going wrong, you don't. You simply don't have the time to putz around.
For the sake of discussion, we are not all comparing apples to apples. A dive to mainland at ginnie, which would use 1 or 2 stages and your backgas to get to the end of it is WAY different than a double stage dive in a low flow, deeper cave.
Also, a distinction needs to be made between Out of gas (you have NO gas) and can't access gas. Those are two different things. Yes, the initial management is to donate whats in your mouth and get that dive gas, but after that, things change. Double roll off? Fixable. Closed isolator? Fixable. Switched to a dead reg? Fixable. A diver truly being out of gas is a rare event, esp with the isolation manifold.
However, diving thirds in stages removes flexibility. If you're on a 3 stage dive, and your buddy truly loses all of his backgas, by the time you're near the entrance, you've got 2 stages with 1000psi each, and another with somewhere around that. Slow. Slow. Slow.
Similarly, if you are on the same dive diving 1/2+200, and your bud loses all his backgas, having them exit on the stages results in multiple OOG (really OUT) unless they are super zen with that stellar sac rate they had on the way in. Not realistic.
Or... you put them on the long hose and tow out. Your double 104s have enough gas to cover 7-8 stages. Wow. (288cuft/32.5cuft used per stage = 8.somethin). Your buddy wont run out. You manage the stages, jettisoning them as you use them, and switching to your backup if the stage empties. This can all be done one handed while on the trigger.
Change gears now. We're doing that mainland dive, and my buddy suffers a rare double burst disk failure and loses all the BG at 4000ft in, and now we're sharing out. Diving thirds on stages and thirds in your back gets you almost to the stage cache' at 3000. Fail. Your sac rate and swim rate simply won't be the same. But... if we reserve 100psi per stage as I suggested earlier, you get to the stage cache with a few hundred psi reserve. Even if your sac increases, you'll make it. Awesome. You get on your stage and high-tail it out, leaving the empty stages as you use them (1 or 2, which ever).
Thank GOD total losses of backgas don't happen. The isolation manifold covers you and always saves half (or close to it) of your gas, no matter what. A freeflowing reg empties an al80 in something like 90 seconds at depth (something like that, I don't have the article in front of me). Thats no joke. Being able to shut that down and still access the gas in the tank is a huge plus. No futzing around with swapping regs and such, just the twist of the wrist.
While most anything will work in shallow caves, things change when deeper. 1000psi in ginnie does not equal 1000psi in Eagles Nest. An entire stage will last a staggering 17 minutes at 280ft (.5 sac rate), and if you think you have a .5 when things are REALLY going wrong, you don't. You simply don't have the time to putz around.
For the sake of discussion, we are not all comparing apples to apples. A dive to mainland at ginnie, which would use 1 or 2 stages and your backgas to get to the end of it is WAY different than a double stage dive in a low flow, deeper cave.
Also, a distinction needs to be made between Out of gas (you have NO gas) and can't access gas. Those are two different things. Yes, the initial management is to donate whats in your mouth and get that dive gas, but after that, things change. Double roll off? Fixable. Closed isolator? Fixable. Switched to a dead reg? Fixable. A diver truly being out of gas is a rare event, esp with the isolation manifold.
However, diving thirds in stages removes flexibility. If you're on a 3 stage dive, and your buddy truly loses all of his backgas, by the time you're near the entrance, you've got 2 stages with 1000psi each, and another with somewhere around that. Slow. Slow. Slow.
Similarly, if you are on the same dive diving 1/2+200, and your bud loses all his backgas, having them exit on the stages results in multiple OOG (really OUT) unless they are super zen with that stellar sac rate they had on the way in. Not realistic.
Or... you put them on the long hose and tow out. Your double 104s have enough gas to cover 7-8 stages. Wow. (288cuft/32.5cuft used per stage = 8.somethin). Your buddy wont run out. You manage the stages, jettisoning them as you use them, and switching to your backup if the stage empties. This can all be done one handed while on the trigger.
Change gears now. We're doing that mainland dive, and my buddy suffers a rare double burst disk failure and loses all the BG at 4000ft in, and now we're sharing out. Diving thirds on stages and thirds in your back gets you almost to the stage cache' at 3000. Fail. Your sac rate and swim rate simply won't be the same. But... if we reserve 100psi per stage as I suggested earlier, you get to the stage cache with a few hundred psi reserve. Even if your sac increases, you'll make it. Awesome. You get on your stage and high-tail it out, leaving the empty stages as you use them (1 or 2, which ever).
Thank GOD total losses of backgas don't happen. The isolation manifold covers you and always saves half (or close to it) of your gas, no matter what. A freeflowing reg empties an al80 in something like 90 seconds at depth (something like that, I don't have the article in front of me). Thats no joke. Being able to shut that down and still access the gas in the tank is a huge plus. No futzing around with swapping regs and such, just the twist of the wrist.
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FWIW-I teach gas sharing side by side in my cave DPV course. Both scooters running, which expedites the exit.
Speed matching was already done in the initial part of the dive.
If one person has a stage with gas, it of course is passed off after long hose deployment & things settle down a bit.
The receiver ALWAYS holds onto the long hose (if gas sharing)during the exit, just as with normal swim exiting.
If negotiating a restriction then gas sharing on the scooters is done "in-Line" with the donor in back. Once through the restriction, go back to a side by side exit.
Speed matching was already done in the initial part of the dive.
If one person has a stage with gas, it of course is passed off after long hose deployment & things settle down a bit.
The receiver ALWAYS holds onto the long hose (if gas sharing)during the exit, just as with normal swim exiting.
If negotiating a restriction then gas sharing on the scooters is done "in-Line" with the donor in back. Once through the restriction, go back to a side by side exit.
ucfdiver
Contributor
FWIW, 1/2+200 vs 1/3rds stage math really makes less than 2 minutes of difference at 200ft. I think these discussions come up so often that we can lose track of that. I think it matters, but if we spent as much time doing valve drills as we did arguing over 7cu ft of gas, we'd never have an OOA situation anyways.
For more perspective, if your SPG is off 2.4% through any of the dive, it's a bigger deal. If you don't account for how low you can breathe your tanks (IE you can't access gas at 100psi), that's a bigger deal. If you take an extra 7-8 seconds isolating a failure at depth, that's a bigger deal.
For more perspective, if your SPG is off 2.4% through any of the dive, it's a bigger deal. If you don't account for how low you can breathe your tanks (IE you can't access gas at 100psi), that's a bigger deal. If you take an extra 7-8 seconds isolating a failure at depth, that's a bigger deal.
OP
PfcAJ
Contributor
What happens when multiple scooters come into the mix? You can't speed match the 2nd scooter the same way while inside the cave without some stop and starts.
ucfdiver
Contributor
I think a very light tap on the "pitch hub" while moving allows you to match speeds effectively with very little stopping and starting.
Plus most double scooter dives I'm aware of would have multiple stage bottles in the cave and I guess you'd be off the long hose by the time you're back to the scooter drop, no?
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