Stand alone secondary computer use

[broncobowsher]

I'd be bending my backup if I did that. For my diving, with both my live deco and my standalone on 50/70 GF I would have about 10-12 more minutes of deco at 1.2 vs 1.3 on the standalone.
eg if I run 1.3 on the wreck and follow my live deco shearwater then my standalone set at 1.2 will be bent around the 20ft stop and continue to be bent all the way to the surface. Usually the deeper stops are close enough that I can clear them within a minute but the longer slower tissues are not clearing as readily and it adds up to a total of ~10-12mins more typically spread across the 30-10ft stops.

I don't see that as a problem. If you are switching to the stand alone you are having major problems (controller died). And extra 10 minutes of deco would probably be a good thing. That would be a lot better then if things were slightly the other way, computer saying all is good when you really should be spending another 10 minutes at the last stop.

 

[rjack321]

shrugs, I dont know what you would intentionally set the standalone to a setpoint you aren't following. Some people only use a standalone for deco, I did that for almost a year. I set it to mimic my actual setpoint. I dont want to bend the standalone on dives when I follow my primary live deco. It would hate me for repetitive dives and serves no purpose to bend it.

 

[jale]

I personaly don't use a live computer.
I just have a ppo2 monitor and a SA computer.
I try to keep my set point at 1.2 avg and set the SA at 1.0. On the way up, in the upper deco section, i reset the setpoint to 1.3-1.5.
If I dive with OC, i am qute close to them...

 

[tbone1004]

@rddvet mine is set for manual switch from 1.0 to 1.4. I try to run 1.1 *the least annoying HUD setting on my Meg*. My backup computers are set at 1.0 to give a bit more conservative deco and since I run between 1.0 and 1.1.
The "high" setpoint is 1.3 for deco and I switch when I start deco. That one is a bit complicated since I try to do as much of my deco at 10ft, so have a max of 1.3. Rare to have any big gap in the two, always less than 5 minutes.

I would consider starting out with a loop full of O2 if I were you. Easier to deal with your 1.6ppO2 check at 20ft, but also minimizes risk when using hypoxic dil.

@broncobowsher if you can't remember to change your computer from CC to BO you shouldn't be diving a CCR. That should be ingrained in your bailout procedure. Shut DSV/BOV and switch to OC. Turn off O2. Change computers. Signal buddy you've bailed out and O2 is off.
If you are diving at depths where your dil ppO2 may be .7 or .8 and that is a massive difference in deco obligations.

 

[doctormike]

I've also had a few people tell me that they run their backup in OC mode with whatever BO gas they're carrying. The thought process being that if the crap hits the fan you may forget to switch a computer to BO mode, thus affecting the deco obligation. Doing that seems silly to me.

Yup. If you do that and are diving to 110 feet, running your manual CCR at PO2=1.0 and your deep bailout is EAN32, then your backup will think that you have been diving at PO2=1.4, right? If you have to bail out and follow the backup, you will be skipping a lot of deco...

 

[doctormike]

if you can't remember to change your computer from CC to BO you shouldn't be diving a CCR. That should be ingrained in your bailout procedure. Shut DSV/BOV and switch to OC. Turn off O2. Change computers. Signal buddy you've bailed out and O2 is off.

I never learned to shut off the O2 as a routine for bailout, but I'm always willing to consider new things. I would be concerned about forgetting that it was off if you went back on the loop, but I guess if you were watching your PO2 you would pick that up.

Is that to keep it from filling the loop and affecting buoyancy? I guess it depends on what the issue was. If it was a stuck open solenoid, or some other internal leak, that might be an issue between loop vents, right? I think that the JJ defaults to low setpoint if it loses the controller, so as long as the cells are working, that shouldn't be a problem if you are bailed out.

 

[tbone1004]

@doctormike if you're on mCCR's you need to shut the leaky valve off. If on eCCR, and remember that my primary diving is in a cave, the ups and downs of the cave can cause an eCCR to go a little haywire with ppO2. If you're going to get back on the loop, you'll check the ppO2 anyway so why run the risk of having the unit try to mess with your buoyancy control on top of it

 

[doctormike]

Yeah, that’s what I figured, a tradeoff. Diving eCCR in the ocean only, that never came up in training but it makes sense. Of course, you could have a breathable PO2 with the O2 off, though, but you should see it drop and figure it out. That was the point in the thread about the instructor shutting off O2 in training....

 

[JonG1]

I am in the process of including a back-up standalone too and have a thread running on a UK forum. It is quite popular over here to run a similar target PPO2 on the back-up, but set the gradient factor to 90/90 or 99/99. That way you always have a known minimum deco plan available that can always be padded if needs be.

GF99 monitoring is possible via the SW, but this is realtime as opposed to having a structured set out escape plan on min deco.

Plus should never bend the stand alone!

 

[doctormike]

If you can afford it, NERD is a good backup. It knows your real PO2, it’s great to have all that info at HUD level, especially for photographers. And you can use it even if you have to go off the loop...

AFIK, it should work for deco even if the CANbus gets cut, it’s powered outside of the rebreather.