How do you calculate when to turn when using a scooter on OC?

[Dsix36]

I know that turning on thirds (or even sooner if conditions dictate) is the most common approch to OC cave diving but what changes when you scooter. Suddenly you get much further into the cave before you ever hit thirds. There is no way you have enough gas to swim out if the scooter dies. Knowing your SAC rate, swim rate, and gas amounts makes for easy calculation of the distance you can swim with given amounts of gas BUT Y0ou are using gas as you go into the cave (and this can vary from day to day and dive to dive) so how can you truly plan when to turn in a realistic manner that is acceptable,

Very simplified example: swim @ 50fpm, scooter @ 150fpm, SAC @ .5, 160 cf of gas @ 3000psi, 4ATA
Swimming =Thirds is at 2000psi in 20 minutes with 1000' of penetration
Scootering =Thirds is at 2000psi in 20 minutes with 3000' of penetration

Simple logic tell me that is an easy way to die so one must plan according having enough gas to swim out but it can never be a linear plan due to variables of each dive. Turning must be done on thirds of the lowest common denominator. Scootering to 1000' and turning will be way early of 1/3 of my gas supply and at the end of my dive is when I will finally reach thirds. Meaning I turned at sixths. Is there a simple magic formula to calculate proper turn time on the fly?

RB diving is simple since I never touch my OC gas and thus I still have full tanks at only penetration.

OK, let the keyboard warriors attack for asking for online training etc. I have thick skin and really do not care. It will be fun to see how the different replies tally up

 

[rddvet]

At this point I am starting to think OC with a scooter is just stupid when I can just take my rebreather. T

That's kinda where I'm at. I've been doing a little more OC diving lately and did a oc scooter dive to about 3000' in ginnie. Nothing crazy, but once I was around 2500' my brain started questioning whether going further is really a wise idea if I happen to get a scooter failue. Only difference is I was in a buddy team, but I would still prefer not to get towed out. Oddly enough when we got home one of our scooters had a battery error, but luckily it was a heat warning from being in the truck a little longer than it should have been. But it was a tiny little reminder of what can happen pushing distance (not that 3000' in ginnie is pushing distance in most peoples eyes).
But main point is, yeah I feel more safe scootering on the rebreather. Whether or not that's really safer or just a feeling is up for debate.

 

[tbone1004]

Please tell me you're joking

We aren't all diving Ginnie - sometimes swimming out is actually impossible. When you "must" scooter out you can rely on being towed (with the right buddy/scooter/cave) and/or bring backup scooter(s). The swimming gas consumption isn't relevant anymore.

Not joking at all, and rarely am I diving Ginnie. You can't just say "bring stages and a backup scooter" and you'll be fine. You have to actually plan the gas when you're on a DPV, same as a CCR. Sure you can have a team backup DPV which is great, but you don't always need or want stages, and you still aren't setting an actual penetration limit with that strategy. I've been on too many DPV dives where the exit was slower than the entrance, largely due to people towing a DPV with bad technique, you can't just go dive thirds on these things and hope it's going to buff out.
I do a lot of 5k+ ft penetrations, backup dpv's required, it's not coming from a lack of experience. I never said you had to plan the gas to swim out, I said you actually had to do the math. That math could well be 100fpm exit speed, but it damned well better not be 150fpm or more unless you're in wide open power cave. The ratios are a function of entrance speed vs exit speed and you can't rely on the exit being the same or faster than the entrance. I've had too many big cave dive exits drastically slowed down because of silt outs that were not seen on the entrance because the guys in back created a massive mess. Exit was still on a DPV but barely faster than we could kick because visibility was so bad.

 

[flymolo]

Not joking at all, and rarely am I diving Ginnie. You can't just say "bring stages and a backup scooter" and you'll be fine.

dude we know. nobody is saying just bring stages and a backup scooter and you'll be fine. that's kind of a ridiculous assertion.

 

[rjack321]

Not joking at all, and rarely am I diving Ginnie. You can't just say "bring stages and a backup scooter" and you'll be fine. You have to actually plan the gas when you're on a DPV, same as a CCR. Sure you can have a team backup DPV which is great, but you don't always need or want stages, and you still aren't setting an actual penetration limit with that strategy. I've been on too many DPV dives where the exit was slower than the entrance, largely due to people towing a DPV with bad technique, you can't just go dive thirds on these things and hope it's going to buff out.
I do a lot of 5k+ ft penetrations, backup dpv's required, it's not coming from a lack of experience. I never said you had to plan the gas to swim out, I said you actually had to do the math. That math could well be 100fpm exit speed, but it damned well better not be 150fpm or more unless you're in wide open power cave. The ratios are a function of entrance speed vs exit speed and you can't rely on the exit being the same or faster than the entrance. I've had too many big cave dive exits drastically slowed down because of silt outs that were not seen on the entrance because the guys in back created a massive mess. Exit was still on a DPV but barely faster than we could kick because visibility was so bad.

Huh? You had to tow the spare scooter on the way in, it makes no sense that towing it on the exit will be radically slower just because it's failed. Unless its flooded or something else is going on. A silt out isn't unique to OC or a scooter either. Like no kidding - 1/3rds is super aggressive. Adding a scooter and towed scooters doesn't change that.

 

[tbone1004]

dude we know. nobody is saying just bring stages and a backup scooter and you'll be fine. that's kind of a ridiculous assertion.

that's literally what he said....

Huh? You had to tow the spare scooter on the way in, it makes no sense that towing it on the exit will be radically slower just because it's failed. Unless its flooded or something else is going on. A silt out isn't unique to OC or a scooter either. Like no kidding - 1/3rds is super aggressive. Adding a scooter and towed scooters doesn't change that.

the diver in the back had bad technique and blew most of the cave out on the way in which mean that even though all gear was fully functional, we couldn't see so the exit was barely faster than if we had kicked in. If the gas planning had been done assuming 150fpm exit speed because we had a spare DPV and we had a 2x safety factor, i.e. 75fpm exit speed, it wouldn't have been enough because the exit was slower than that.

 

[flymolo]

that's literally what he said....

i definitely did not say that simply "bringing stages and a backup scooter" precludes the need for actual planning, and i find it a little strange that you are continuing to insist that i did

 

[tbone1004]

i definitely did not say that simply "bringing stages and a backup scooter" precludes the need for actual planning, and i find it a little strange that you are continuing to insist that i did

all you said was

I was taught to dive stages and bring a backup scooter

Nothing about dive planning in there at all, and since we are in a thread asking how you figure that out, since you didn't say anything useful in your post, it's safe to say the plan is you have a backup dpv and stages so just plan like you would any other dive. I'm not putting words in your mouth, just quoting your post

 

[flymolo]

all you said was


Nothing about dive planning in there at all, and since we are in a thread asking how you figure that out, since you didn't say anything useful in your post, it's safe to say the plan is you have a backup dpv and stages so just plan like you would any other dive. I'm not putting words in your mouth, just quoting your post

Yeah ok

 

[San Diego Climber]

I'm no mod but my third-party $0.02 on the tone here-

flymolo's original comment "dive stages and with backup" does imply that -that's- the plan (it clearly is the entirety of the post, and thus clearly lacks any additional context. this is fact as we can see that that's the post. full stop.) so I don't think jumping on tbone for making assumptions or "putting words into people's mouths" is warranted, nor fair (if he's supposed to make assumptions about what additional planning you're actually doing, then maybe he's also allowed to make assumptions about what additional planning doesn't exist?)

 

[flymolo]

I'm no mod but my third-party $0.02 on the tone here-

flymolo's original comment "dive stages and with backup" does imply that -that's- the plan (it clearly is the entirety of the post, and thus clearly lacks any additional context. this is fact as we can see that that's the post. full stop.) so I don't think jumping on tbone for making assumptions or "putting words into people's mouths" is warranted, nor fair (if he's supposed to make assumptions about what additional planning you're actually doing, then maybe he's also allowed to make assumptions about what additional planning doesn't exist?)

it's my opinion that if you want training advice you should get training and not expect others to give said training advice on the internet