First CCR dive after certification, 145 days since last dive.

[Mastow1]

Pre-dive:

Reviewed all course work and detailed OptimaCM & NomadLS BC at home. Took on and off several times. Studied Shearwater manuals and configured computers, practiced dive planning with DiveCAN and Petrel BU computer. Executed survival and preflight checklist several times. Neighbors are wondering what I was doing in the garage.

Dive: Pre-staged aluminum 40 diluent and OC cylinders with mask and fins on the distant dive platform. Briefed none CCR diver on air sharing procedures. Tangled DiveCAN wires while suiting up. Verified survival checklist and conducted preflight and breathed CCR while on surface. Immediately noticed that 6 pounds of weight in spine of Nomad is too heavy. Trim was excellent, but buoyancy control was a bitch because of air to compensate for excess weight. Buddy noticed I vented a lot of air on dive (I didn’t think Rebreathers produce bubbles). ADV worked predictably, but vented to reduce loop volume and turned off the ADV for part of the dive. Practiced with all vents and dive valves. Need to build proficiency in finding valves. Face mask with purge valve worked perfectly. Butt tightened considerably when I couldn’t quickly locate ADV slider to turn on, several (BUT LONG) seconds after I needed it. Compensating bubble in BC made for unpleasant buoyancy control issues.

ADV worked on descent, but activating required hard suck. PPO2 went above 1.2 setpoint, so I stopped and added diluent. I may have changed the setpoint prematurely. HUD came loose twice and was not ideally positioned in my view.

Other than sloppy technique, the only significant error I made was to leave backup computer on bailout. Ended dive after 47 minutes because of boredom. Video of diving indicated struggle with buoyancy control, mediocre fin techniques, relatively large bubble in back of BC and showed the aluminum tanks almost perpendicular to my body. Should be parallel at side. Could not locate the .19 PPO2 setting immediately after the dive. DiveCAN may have been too wet. Surprised the CNS after dive was 21%

Dive accomplish all I wanted E.G. familiarization with system. Very impressed with and have great confidence in equipment. Mistress is great fun, expensive and demanding of attention, but did not try to kill me, this time.

To do: Replace DiveCAN and HUD batteries. Do leak down test of diluent ADV. Remove 2-4 pounds lead from BC. Practice and develop muscle memory for all controls. Re-rig aluminum cylinders to stay parallel to body.

 

[_Ralph]

It gets easier the more you dive

You’ll use less DIL, less O2, less bubbles....

You’ll develop the muscle memory to find your valves, MAV, shutoffs, etc.

As you get more comfortable, you will know how to control that extra weight better... I remember being a few pounds heavy on the first day of training... got it sorted on the second day, then added 3 bailouts on the last day and was able to manage that extra weight just fine....


_R

 

[broncobowsher]

The .19 PPO2 issue is common. Thinks you are still in the water and blocks that option. Were you truly out of the water or still bobbing on the surface? I have to be truly out of the water for a couple minutes.

Everything else sounds just like when I started putting hours on a couple years ago.

 

[tbone1004]

the ADV doesn't vent, only adds. The OPV vents. That is a function of you not being comfortable and not paying attention to min loop volume.

Order of operations with the CCR for me with regards to buoyancy
Min Loop-This is the one that will try to kill you if you aren't careful with potentially wild ppO2 swings, but is also the most frustrating to deal with. Keep min loop under control. ADV off if you have a MAV or make it stiffer if you don't so you don't have to shut it off. Put your primary focus here
Drysuit-if you have one, maintain min volume on drysuit.
BCD-after you keep the other two under control, THEN you pay attention to your buoyancy on the BCD. You'll add and dump a LOT while you get used to this thing, but you want to do everything you can to maintain buoyancy from the BCD instead of the other two.

Focus on min-loop and ppO2 stability more than anything while you are on this journey. Only once you are able to control those without getting task loaded will you be able to get your buoyancy/trim/propulsion under control.

Surface setpoint is going to be an issue. Set the unit to 0.7, and O2 flush when you get to the surface. It will keep the unit calm until you're fully out of the water.

CNS sounds about right if you were running that high of a ppO2, it racks up quick.

If you have a high ppO2, and I assume it wasn't above 1.6, then just breathe it down. It will take a while, but if it's 1.3 or 1.4, just breathe it down. No sense in wasting dil and O2 to get back to "perfect setpoint". If you're going to drop it back down for practice, or if you have it a lot higher than you're comfortable with, make sure you dump gas from the loop first. Get back to min loop if you aren't there already, then exhale some portion of a breath from your lungs, then add dil. Over time you will learn how much of a breath you need to make the change *1/4, 1/2, etc depending on depth and how high the ppO2 was as a function of the ppO2 of the dil*.
f you add dil before you vent, then you have a less effective drop in ppO2 because the dil has more gas to dilute so you have to add more to get it down, but then you have to vent a lot more total gas out of your nose to get back to min-loop volume. This also compounds buoyancy issues as you are changing the loop volume and if you're shallow can cause you to feel like you're on a merry go round.

 

[rjack321]

If you only have an al40 just use your drysuit for buoyancy control. If you step up to an al80 start splitting the buoyancy between suit and wing. As you add more BO use your wing for the big changes and fine tune with your suit.