O2ptimaCM and Trim

[LFMarm]

It is standard procedure on the ChOptima to close in line shut off valve after reaching the bottom for the exact reasons mentioned in this thread.

 

[addohm]

It is standard procedure on the ChOptima to close in line shut off valve after reaching the bottom for the exact reasons mentioned in this thread.

That's not what I was taught and also not ideal in a sawtooth dive profile. I think the MAV is better then the ADV\MAV in this regard. For square profiles, its super easy. None of my dives are "super easy". lol I found today that using the MAV was better for my dive and I actually don't have to use it very much. Certainly not as much as I hear the ADV\MAV firing.

Also, I did started closing my o2 during deco and just manually adding to keep a 1.6-ish PO2.

Today I did a little experiment after a 2.5 hour dive. I bailed out after my deco was finished and my trim and buoyancy was very good. I wasnt head up, or head down. I was just neutral, comfortable and relaxed. The moment I switch back to the rebreather, my buoyancy and trim are all over the place. I did my best to make sure I wasn't adding loop volume when I switched back. So, I know I don't need to adjust my kit. I just need something in my brain to click; some deep, thorough and technical understanding. Here a clip: (ready to be trashed).

Note: I am holding onto my bailout deco cylinder in my left hand to offset the buoyancy of my short hose sidemount cylinder.

 

[mr_v]

Also, I did started closing my o2 during deco and just manually adding to keep a 1.6-ish PO2.

Why close O2?

 

[addohm]

Why close O2?

So I know exactly when gas is being added to the loop, and how much.

 

[LFMarm]

That's not what I was taught and also not ideal in a sawtooth dive profile. I think the MAV is better then the ADV\MAV in this regard. For square profiles, its super easy. None of my dives are "super easy". lol I found today that using the MAV was better for my dive and I actually don't have to use it very much. Certainly not as much as I hear the ADV\MAV firing.

Fully agree, only for square profiles.

 

[LFMarm]

Also, I did started closing my o2 during deco and just manually adding to keep a 1.6-ish PO2.

During deco I also manually control pO2 but instead of shutting off the solenoid, I switch to a low set point (0.5-0.7) so that the solenoid becomes a parachute but never fires if you keep pO2 high manually.

 

[addohm]

What things do you guys do that helps you find that perfect neutral buoyancy sweet spot on the rebreather for sawtooth dive profiles? I can never seem to find it. Always just slightly negative or slightly positive or worse. Even with the MAV and closed o2 I struggle to find that perfect buoyancy when still.

 

[PEDiver]

The crack pressure on mine is set to the "maximum" (e.g. lungs have to be collapsing for it to fill) but it still causes problems like Tracy stated. My instructor\course director suggested I go full MAV to help isolate areas that I need to address.

FWIW, when I had my Choptima, I switched to the MAV and got rid of the ADV. Most of the other Choptima divers in my circle also did the same thing.

 

[addohm]

FWIW, when I had my Choptima, I switched to the MAV and got rid of the ADV. Most of the other Choptima divers in my circle also did the same thing.

I have already switched to the MAV and it's just better for the profiles of my dives. I don't see myself ever switching back.

 

[lostsheep]

What things do you guys do that helps you find that perfect neutral buoyancy sweet spot on the rebreather for sawtooth dive profiles? I can never seem to find it. Always just slightly negative or slightly positive or worse. Even with the MAV and closed o2 I struggle to find that perfect buoyancy when still.

No ADV, minimum loop volume, tiny adjustments and practice.

Edit: with practice you’ll just instinctively anticipate needed changes.

When I’m close, sometimes I’ll swim TO the depth the rebreather wants to be at.