O2ptimaCM and Trim

[grantmac]

AL80s for dil and offboard bailout and AL13 o2.

I was thinking perhaps lp50s, which would trim heavier in the feet.

 

[justinthedeeps]

Thanks for your detailed response. I actually changed my ADV\MAV out with an MAV only valve to counter this. I thought the same thing. Too much air in the loop causing my torso to be very buoyant. At least, that was the idea. Yesterday I did a 2.5 hr dive and shifting the unit downward definitely did not help, but having an MAV only definitely helped keep the loop volume at minimum. I don't like having to press another button, especially with my already busy hands leading cave dives, but I managed. Im going to continue on with the MAV anyway. Using a drysuit down here is really not an option for me.

How would deleting the ADV 'fix' buoyancy/trim/WOB?
If an ADV is acting up on a well designed rebreather, it might be a good indication that *something else* needs to be fixed instead?

 

[Tracy]

How would deleting the ADV 'fix' buoyancy/trim/WOB?
If an ADV is acting up on a well designed rebreather, it might be your best indication that *something else* needs to be fixed instead

The ADV on the Choptima isn't ideal due to positioning. When your entire rebreather is below you, you can't mount the ADV in an optimal position.
For that reason, it needs to be turned off after the descent or it will continue to leak throughout the dive.

 

[justinthedeeps]

there's no chance for me to be wearing my dry suit. Its just too damn warm down here

I just did 20 shore dives in a drysuit with 28-30ºC air and water temps every day as an experiment, it wasn't so bad. Wear the thinnest thermals you can find, cut down on lead, and soak the suit as soon you zip it up (evaporative cooling)

This not uncommon in some places (SE Asia)
Buoyancy is great at all depths
It is cleaner (but always flush the p-valve!)
Dries faster (trilam) But keep it out of the sun/UV (as with any gear/skin you care about)

 

[justinthedeeps]

The ADV on the Choptima isn't ideal due to positioning. When your entire rebreather is below you, you can't mount the ADV in an optimal position.
For that reason, it needs to be turned off after the descent or it will continue to leak throughout the dive.

Can the crack pressure be adjusted, instead of completely closed/deleted? How is this managed on other chestmount CCRs?
But also to the point, should we be closing/modifying/deleting ADVs before addressing other fundamental aspects of trim, unit positioning etc?

 

[Tracy]

Can the crack pressure be adjusted, instead of completely closed/deleted? How is this managed on other chestmount CCRs?
But also to the point, should we be closing/modifying/deleting ADVs before addressing other fundamental aspects of trim, unit positioning etc?

Yes, it can be adjusted, but it is still going to be overly sensitive due to being 3" below your lungs.
I would guess most don't have an adv? I don't think the triton or FX have an adv and it is optional on the OptimaCM.
Closing the ADV when you get to the bottom is standard practice across every unit I have been trained on. On conventional units, personally I detune them and leave them on all the time but that doesn't work on the CM. It isn't a standard backmount unit, you can't just assume it is and dive it that way.

 

[justinthedeeps]

Thanks for sharing your thoughts and tips on ADVs
It doesn't sound like that fixed the OPs problem, but I guess it could help to isolate it.

Symbios seems to have ADV?

Cutting the Wires on Halcyon’s new Chestmount Rebreather

Halcyon Manufacturing is close to rolling out its innovative new chest mount closed circuit rebreather (CCR), which will be on display at the annual DEMA diving trade show this month. Tech and cave instructor John Kendall, who has been working with the new unit, and helped steer it to launch...

indepthmag.com

 

[Tracy]

Thanks for sharing your thoughts and tips on ADVs
It doesn't sound like that fixed the OPs problem, but I guess it could help to isolate it.

Symbios seems to have ADV?

Cutting the Wires on Halcyon’s new Chestmount Rebreather

Halcyon Manufacturing is close to rolling out its innovative new chest mount closed circuit rebreather (CCR), which will be on display at the annual DEMA diving trade show this month. Tech and cave instructor John Kendall, who has been working with the new unit, and helped steer it to launch...

indepthmag.com

Sorry. I was referring to units that exist. As in something you can buy and go dive.

 

[Fat old english bloke]

Yes, it can be adjusted, but it is still going to be overly sensitive due to being 3" below your lungs.
I would guess most don't have an adv? I don't think the triton or FX have an adv and it is optional on the OptimaCM.
Closing the ADV when you get to the bottom is standard practice across every unit I have been trained on. On conventional units, personally I detune them and leave them on all the time but that doesn't work on the CM. It isn't a standard backmount unit, you can't just assume it is and dive it that way.

Triton has an ADV and it too gets closed.

 

[addohm]

Can the crack pressure be adjusted, instead of completely closed/deleted? How is this managed on other chestmount CCRs?
But also to the point, should we be closing/modifying/deleting ADVs before addressing other fundamental aspects of trim, unit positioning etc?

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.