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

 

[flymolo]

I was taught to dive stages and bring a backup scooter

 

[Seameadow]

Reference Manatee diver, In case you missed it:

Kens article

A great resource!

 

[rddvet]

I find it very similar to ccr planning. Figure out the radius of where you can safely get to and swim back oc if you need to. I know it’s not exactly the same but it’s a pretty safe way to do it. Funny enough gas planning was a very small subject in my class with a very famous instructor. In retrospect I think it should have been covered more and years later I don’t agree with that instructor’s planning strategy.
As has been said it’s a mixed bag and 10 instructors likely teach 8 different ways. It’s why people have gone to places like sweet surprise without enough gas and died

 

[Dsix36]

I find it very similar to ccr planning. Figure out the radius of where you can safely get to and swim back oc if you need to. I know it’s not exactly the same but it’s a pretty safe way to do it. Funny enough gas planning was a very small subject in my class with a very famous instructor. In retrospect I think it should have been covered more and years later I don’t agree with that instructor’s planning strategy.
As has been said it’s a mixed bag and 10 instructors likely teach 8 different ways. It’s why people have gone to places like sweet surprise without enough gas and died

It is very similar to CCR bailout planning with the exception that now you are using some of your bailout on the way in, so it is much more dynamic and hard to plan in advance.

 

[grantmac]

Is planning penetration based on battery capacity/run time really realistic compared to a failure which isn't based on capacity? Because it seems like any decent DPV will have the capacity to get you really far back in a cave without coming close to using even 1/3rd of it's capacity?
Although I must admit my DPV experience doesn't involve caves and is on a unit with any exceptionally long range.

 

[tbone1004]

I was taught to dive stages and bring a backup scooter

That's not a real strategy, recommend you actually do the math....

It is very similar to CCR bailout planning with the exception that now you are using some of your bailout on the way in, so it is much more dynamic and hard to plan in advance.

Not all that different. With CCR you set your radius based on gas you're carrying, with OC DPV you set the minimum gas needed based on your planned radius, so same formula just rearranged to solve for a different variable at least for the min bailout. You then add on what you actually plan to use on top of that.

Is planning penetration based on battery capacity/run time really realistic compared to a failure which isn't based on capacity? Because it seems like any decent DPV will have the capacity to get you really far back in a cave without coming close to using even 1/3rd of it's capacity?
Although I must admit my DPV experience doesn't involve caves and is on a unit with any exceptionally long range.

The batteries now are all pretty insane, we aren't planning based on Tekna's or UV18's anymore, the range on the modern DPV's is nuts, even the Blacktips will get you stupid far back and the lithium batteries are much more stable than lead was. The DPV's are also run very differently now than they used to be, variable pitch props was great for something easy to let you change speed but was not efficient since the motor still spun at direct battery voltage, now that they are true variable speed the efficiency improvements are wild.

 

[rjack321]

Is planning penetration based on battery capacity/run time really realistic compared to a failure which isn't based on capacity? Because it seems like any decent DPV will have the capacity to get you really far back in a cave without coming close to using even 1/3rd of it's capacity?
Although I must admit my DPV experience doesn't involve caves and is on a unit with any exceptionally long range.

The battery is not the limiting factor failure mode anymore compared to SLA scooters of yesteryear (apart from something like the Seacraft GO). Trigger switches, props and other less "minutes runtime" based factors are the limitations. Scooters can and will still fail. Backup scooters and having buddies with good enough scooters to actually tow 2 divers at cave speeds (150ft/min) is imperative.

Having one diver on a Seacraft or Genesis and the 2nd diver on an SLA UV26 and 3000ft back is super problematic since the UV26 can't tow 2 worth a damn. Having both on high end scooters which can tow impacts both diver's plans.

 

[flymolo]

That's not a real strategy, recommend you actually do the math....

Please tell me you're joking

 

[rjack321]

That's not a real strategy, recommend you actually do the math....

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.

 

[flymolo]

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.

Indeed