Been having a significant itch that needed to be scratched; changing from backmount CCR to chestmount CCR. According to my "heart" it means a rebreather that is:
- lightweight for travel and logistics;
- is flexible for configuration be it sidemount, backmounted twinset/doubles diluent, even single cylinder recreational;
- can do moderate deeper trimix dives (smaller scrubber than backmount);
- and will work in caves and overhead restrictions (simply flip forwards and push though)
That's a tall order with big claims made. Wonder if there's any drawbacks (aside from the positive pressure breathing)?
A test dive is by far the best way of checking out these claims, so arranged a dive on a Triton chestmount rebreather in a local diving lake under the supervision of the owner and another diver.
Used an XDeep sidemount harness with a couple of 8.5 litre steel cylinders configured with my normal sidemount regulators. For the first dive, I dived purely on my sidemount open-circuit configuration with no Triton attached so I could ensure weighting and kit is all dialled in. That diving lake is very intolerant of poor finning with any mistakes punished with a cloud of silt.
I'm a moderately experienced rebreather diver with around 400 hours on my "hybrid" Revo rebreather in the sea on wrecks (down to MOD2+ depths, ~70m/230ft) and caves (have CCR Cave certification). Have plenty of open circuit experience with trimix and overhead, mainly in the sea. My Revo has a Petrel and Nerd HUD.
The Triton rebreather is fully manual with a Petrel monitor and the Triton flashy-light HUD. The unit is attached to the harness with four boltshaps, two on the top chest D-rings and two boltsnaps on bungees to D-rings on the harness waistbeilt. Diluent is supplied via an offboard BCD connector on the LHS running from the LH sidemount cylinder which has a regulator on a short hose with a bungee necklace). Oxygen is supplied onboard from a 2 litre steel cylinder clipped to the bottom of the Triton.
The dive.
For the test dive, I kitted up into the sidemount harness and attached the cylinders in waist deep water on a ramp. The Triton was then clipped on, offboard diluent connected & tested and pre-dive checked -- pretty generic rebreather checks.
The first descent was interesting. Firstly, the oxygen and diluent injection was unfamiliar, so I was too slow to get the system into equilibrium. On a rebreather there's the drysuit and wing for buoyancy, plus the rebreather with the loop volume and oxygen content to manage. As the ramp ends at 3m/10ft it was easier to just stop on the bottom to sort things out; at least I wasn't underweighted! On a dive like this there's no need for excess weight to be managed by the wing, so the drysuit is easier for buoyancy adjustments... but only if I could find the drysuit inflate hidden behind the chestmounted rebreather with its myriad hoses and cables.
Getting the loop sorted was easy enough, just getting used to where the oxygen manual add button was (it's a manual rebreather, so no solenoid) and the diluent button on the ADV (automatic diluent valve) which has a shutoff for the ADV. All fine after a few seconds to sort out the controls and get minimum loop established. Then find the drysuit inflate and get neutral in the water.
Gently lifting off, it wasn't too bad. Finned towards a sunken cement mixer for a few minutes. Was difficult as it's my first time with that unit, but nothing an hour or two on the unit would resolve.
We ascended to get our bearings and get to another platform. This is where sidemount is a royal PITA as the wing is over the small of your back and when inflated on the surface it pushes you face down with the chestmount dragging you even more forwards. Had to flip over and lay more-or-less on my back whilst we worked out where we were going and swimming towards a marker buoy. A backmount unit would counter-balance the wing buoyancy keeping the diver more vertical on the surface. Swam over and descended next to the rope to the platform 6m/20ft below. This descent was fine; I had got the hang of the manual adds and had worked out where my drysuit inflate was hiding (was difficult to find throughout the dive). Once at the platform, did the standard thing and backed away from the platform using the edge for a reference. Was stable but uncomfortable as there's no finesse to managing the loop volume which is very much a learned skill.
Trim.
I normally dive pretty flat in the water, especially in silty conditions as you would stir up the bottom if not flat. I found that I was definitely head down, maybe 10 degrees, with my legs pooling gas around my feet. As ever, this makes dumping gas difficult as you need your legs below your torso to get the bubble out of the shoulder dump. I think that there's some work to be done with the position of the Triton relative to my torso; maybe moving it down a bit would help to place it to get my centre of buoyancy shifted downwards. If there is a next time I know to spend more time faffing -- the definition of sidemount! One other 'theory' I've had is that maybe the Triton was too high on my chest; maybe I subconciously added more gas to my drysuit to counteract the trim.
Breathing.
With chestmount the counterlungs are below your chest, so you breathe out to inflate the counterlungs but these are deeper than your own lungs, therefore there's some pressure on your mouth, so inhaling is simple, exhaling on chestmount requires a little more effort than on a backmount rebreather. I spent about 30 mins on that 6m platform doing some vertical movements to see how things worked with changing depth. Was fine, but would be a lot better with a little practice.
Blocked nose.
I did notice that my nasal cavity blocked up by the end of the dive. I use my nose to vent gas from the loop when ascending or adjusting minimum loop volume. This was kind of like a cold which I didn't have; these symptoms disappeared about 10 mins after the dive. I've never had this before (OK, had that on a dive within a couple of weeks of Covid!). I have a feeling this might be due to more pressure on my soft palate with the additional lung pressure. Open to suggestions.
Training.
Generally very happy with the Triton try dive. Would absolutely hate to do a crossover course if I've not got a few hours on the unit beforehand just to get the basics sorted. OK, the instructor/mentor would be able to do some faffing for me, but half of the fun is working stuff out for myself.
From the try dive experience, it is clear that coming to a chestmount rebreather from backmount needs some time to get the basics sorted and dialled in. The rebreather monitoring and injection is pretty much the same as for backmount aside from the configuration.
Should I buy a second hand Triton, I would definitely do a crossover training course which I believe is 3-ish days depending on how things go. However, I'd much prefer to split that into two; the basics (build, checks, mounting, basic shallow diving) which would allow time to get used to the unfamiliar configuration and sort out trim, etc. Then a few weeks later the advanced skills (drills--high/low O2, flushes, dewatering, etc-- flipping forwards, removing & remounting underwater, use in restrictions, etc.).
Things I learned...
- Chest space is crowded
- There's a substantial amount of faffing around required to get the unit and basic skills dialled in. As a reasonably experienced backmount rebreather diver, it's strange to go back to basics.
- Can't easily get to drysuit inflate valve as there's hoses in the way
- Think the necklaced regulator would interfere with the mouthpiece and loop hoses
- Was surprised to find that it was difficult to move my head around with the loop pressing against my head/neck. On backmount it comes over your head; chestmount it floats up.
- The field of view isn't great; I couldn't see the oxygen gauge as the loop and HUD was in the way. Maybe the unit was too high on my chest.
- Found the controls awkward to access, especially with the opposite hand (the Revo's "trumpet" manual add is genius!)
- Snotty nose is a real issue; need more time to find out if this is normal or not; if it is, it's a dealbreaker.
- Definitely dislike the flashy light HUD and really miss the Nerd which has all the info you need right in front of your face, especially the compass! However, a Nerd would be a pain when bailed out as the loop would be stashed behind your head. Thus a backup wrist-mounted Petrel would be essential for decompression calculations.
- AI transmitters just make life so much easier as oxygen pressure is important but very much secondary information. Logging gas consumption is very useful for later reference.
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Edits:
- Split post into two, moved the summary to another post as hit the 10k character limit
- Added pic
I'd spend some time sorting out the mounting.
