O2ptima CM Review

I dove the O2ptima CM shortly before it’s release in 2020. I realized on that demo dive that the successor to the O2ptima rebreather – the chest mounted “choptima” rebreather – was a big deal. It was small, simple and light. It didn’t look quite as cool as other rebreathers underwater but it dove very comfortably and you could carry it around with one hand like a grocery tote.

The choptima earned it’s name because it’s a chest mounted Optima and choptima (or even chop) rolls off the tongue easier. Explorers who were using the backmount O2ptima (now called the boptima) needed something more versatile to navigate tight passages. They used existing boptima parts to fashion a variety of versions of chopshop style rebreathers. They settled on the chest mount and began tweaking and testing until the final form was released.

The really fun part of the choptima is understanding that this unit was created based on a need for niche exploration divers. The insane commercial success – internationally – was a byproduct. It is a representation of what every innovator wants, success based on an honest endeavor to create something good. This good happened to be enabling underwater exploration and the byproduct is a versatile and compact closed circuit rebreather. Dive Rite is an impressive group of innovators that drive passion project after passion project and deliver awesome products to the end consumers. Gimmicky dive gear and benefit-lacking “features” haunt our industry and these guys are chasing real function.

Pros

Human focused design. The chop has a no-tool assembly and disassembly. Bayonet style or hand wheel style connectors mean there’s no excuse to disassemble and reassemble the unit. It takes 10 minutes to teardown, clean and dry. Other units require tools or are even unable to be taken apart to get cleaned. You can inspect the mushroom valves visually, wash and dry the counterlungs, and get the cells dry easily. They did a great job making the unit easy to work with.

Simple operation. The chop doesn’t have any silly engineering solutions that make it complicated. There are 2 buttons. It attaches with a few boltsnaps and a LPI hose.

Extendairs. The choptima has the option to use paper scrubber. This solution is a drop in that requires no packing at all. I have really enjoyed not packing my scrubber but it is nice that I have the option to if needed.

Versatility. Pop it on any rig – sidemount, doubles, single and go dive. The unit is plug and play with your existing system.

Cons

Molex cells. The classic R22D style sensors use a molex connector. Molex connectors have a lot of wires and propensity to wear/corrode.  A coax connector would be an awesome improvement to the unit.

ADV/MAV integration. Points for simplicity are unfortunately paired with an extra step in this case. The integrated ADV and MAV is an extra step in operation when you need to press the dil button (assuming you keep the ADV off most of the time). This is a con, but it’s really not a big deal. I don’t think there is a clean way to accommodate a button mav and an ADV and I am not interested in getting rid of the ADV because it’s useful for ocean diving.

Wet unit. After long dives the unit is wet. It’s the nature of small units. The watertaps do a good job of trapping water intrusion but it’s a wetter unit than backmounted units from my experience.

Tight Spaces

One of the reasons I upgraded to the choptima is the versatility in smaller passages. There are endless debates on what configuration works best in small passages. Chest mount typically isn’t one of the top contenders in that debate. Split can vs sidemounted rebreathers are the standard front runners in the tight space category. Sidemounted rebreathers don’t allow for true sidemount redundancy and I haven’t been happy with any split can designs released. Keep in mind, rebreathers aren’t always the best tool. For shallow or short caves open circuit sidemount may be the better option.

In my opinion, the sidemount-capable-CCR debate is mostly to sound cool and not a product of necessity. I dove backmount CCR in caves and I swam everywhere I could fit – and a few places I couldn’t. Most cave isn’t tiny grindy sidemount-only passage. There are plenty of places where backmount works better because of the passage shape. When you talk to people who do very small restrictions they typically refer to it as “tight and nasty” or something similar. That’s because it’s not fun unless you’re going somewhere particularly cool. It takes a particular skill set, experience level, and mindset to dive sidemount passages and a specific needy to use a rebreather.  There are plenty of big cave passages and buying a unit (especially your first unit) for its ability to do deep sidemount cave dives is like buying an offroad truck with offroad tires as a daily commuter that you might one day take offroad. The gas mileage and wear on your tires make that a silly idea. Some people need a sidemount rebreather for specific dives which is why there’s a market for them but the risks and compromises don’t always weigh out.

With that said, a chest mount unit has many downside to tight passages. You have extra width below you and may need to remove the unit for a “chop-off restriction”. If that smaller area continues you would need to keep pushing the rebreather in front of you the entire time. If you plan to grind through 10in passages in an underwater cave then a chest mount unit wouldn’t necessarily be the best choice (if you actually want to do that then there are many free mental health services available. I suggest contacting them because you need to talk to someone about what you really need to feel complete.).

Despite these restrictions, I decided that the chest mount would work for me in the tighter passages I wanted to see. For small-ish passages, I’m still a thinner profile than a backmount unit. For small passages it works because they’re short (the ones I care about), a minimal part of the dive, and I can handle a little unit pushing in front of me. I am able to navigate those areas and then attach the unit and continue the dive without the compromises of the other options – lack of core sidemount cylinder redundancy or poor design quality. The choptima allows me to be flexible in my mission and I like that.

Takeaway: The chop performs well in tight places without the compromises of other styles of unit.

Chest mount units allow for the ultimate flexibility for gear setup. You can use sidemount, doubles, or even a single cylinder with the choptima. Which one is better? That depends on where you’re diving and your diving philosophy. Fundamentally, manifolded doubles offer the ability to access both cylinders in the event of a regulator failure. Sidemounted cylinders don’t offer this, the cylinders are independent. Isolator bars can fail, giving doubles a chance for catastrophic gas loss. While I’ve seen this failure occur, it is a low chance failure.

Outside of the fundamental differences in gas management between sidemount and backmount, there are two ways to look at configuration choice – surface mobility and underwater mobility. Surface mobility is your ease of entering and existing the water. Underwater mobility is how you manage moving around underwater. Backmount offers better surface mobility when diving off of most boats, especially for hotdrop situations. When penetrating wreck doorways backmounted doubles tend to have better underwater mobility – you can swim through the doorway without turning sideways or removing equipment. In general, it makes more sense to use the choptima with doubles when diving from a boat. When diving drive-up cave sites you can carry cylinders to the water independently – giving you lighter individual loads. For cave diving I prefer to use sidemount with the choptima because it’s easier trips to the water and gives me the ability to move through vertically short passages.

It’s very important to think about surface mobility. People fall over on boats. I’ve seen rebreathers break and people get hurt trying to haul a monster-rig into the water. I’ve also seen people forget important things because they’re too hot and stressed before jumping into the water. Choose equipment that mitigates risk when you get in and out of the water.

Takeaway: The choptima works great on both platforms.

Most of the benefits listed are general takeaways for chest mount units. Why choose the chop specifically? It wasn’t the first chest mount unit.

There are many differences between other chest mount units and the chop that make it superior, but a major reason is US support. Dive Rite is a US company that you can get on the phone and talk to. They’re located in the diving capital of the East Coast and have a history of great customer service and products. At the time of purchase most European chest mount manufacturers had little to no customer support or instructor base. At best it was one person who was “distributor” and instructor.

The chop also underwent years of testing and has independent 3rd party testing as well. Having a few test dives and a homebuilt style don’t tick the boxes to me.

Takeaway: The chop stands out as the superior chest mount unit.

Check out the links below for more information on training and purchasing a unit.