Hollis Prism 2 eCCR Review: A Rebreather That Wants You to Fly It

The Hollis Prism 2 is a closed-circuit rebreather for the diver who wants to learn the machine, not just trust it. It rewards that mindset with a long-duration radial scrubber and a control system built on electronics most tech divers already know. If you want a unit that hides its internals and asks you to trust a black box, this is the wrong rebreather. This one expects you to understand every gas path before you ever put it in the water.

I dive a CCR most weekends off Riviera Beach and Jupiter, so my bias is toward units I can set up, tear down, and troubleshoot myself. The Prism 2 fits that bias, with caveats worth spelling out.

What it is

The Prism 2 is an electronically controlled closed-circuit rebreather, sold in front-mounted (FMCL) and back-mounted (BMCL) counterlung configurations. Hollis ships it without cylinders and suggests two 3-liter steel bottles on board, one oxygen and one diluent. The first stages are color-coded to keep that straight on the bench: green for oxygen, black for diluent, both running an intermediate pressure of 140 to 145 psi.

The numbers that define the envelope: the unit is tested and qualified to 328 ft (100 m) and for water between 39 and 93 degrees Fahrenheit (4 to 34 C). Oxygen control comes from three galvanic O2 sensors with a one-year service life, read by a low-power 0.65-watt solenoid that stays normally closed and only fires when the controller calls for gas. The electronics are Shearwater: Hollis points you to the Shearwater Petrel manual for the head unit, which means the handset logic will feel familiar to anyone who already runs a Shearwater on open circuit.

Two facts you should sit with before buying. First, the scrubber is a user-packed radial design, and the Prism 2 carries no CO2 sensor, so scrubber safety lives entirely in your packing discipline and your respect for factory durations. Second, a fully flooded loop turns the unit roughly 17 pounds (7.7 kg) negative before any added weight, which sets a hard floor on how you balance buoyancy.

What it does well

The radial scrubber is the reason to look at this unit. Gas enters the center tube and radiates outward through the absorbent toward the bucket wall, which gives the granules a long contact path without driving up work of breathing. On a drift along the Jupiter ledges at 90-plus feet, where I want a long, calm bottom time and steady trim in current, that low work of breathing is what keeps the dive boring in the good way. A scrubber you have to fight is a scrubber that ends dives early.

The counterlung choice is real, not marketing. The back-mounted version clears your chest entirely, which matters when you are shooting macro at Blue Heron Bridge and want nothing between you and the sand. The reduced volume of the rear lungs also makes minimum loop volume easier to hold and horizontal trim easier to settle into, which is exactly what a slow BHB muck crawl demands. Front-mounted lungs trade that clean chest for easier in-water access to the bags and drains. Picking the geometry to match the diving you actually do is a privilege most rebreathers do not offer.

The dual independent monitoring is the design choice I respect most. The solenoid system runs on two 9-volt alkalines wired in parallel; the heads-up display runs off its own Saft 3.6-volt lithium cell in a separate compartment. Flooding is the chronic weakness of any rebreather with an opened battery bay, and Hollis answered it by giving you two electrically separate systems. If one battery compartment floods on a dive, you switch to the other display and end the dive in control instead of guessing. That is the kind of redundancy you appreciate at a 20-minute deco obligation, not on the surface.

Where it falls short

No CO2 monitoring is the headline limitation. The manual is blunt that the Prism 2 has no technology to detect dangerous CO2 in the loop, and that exceeding scrubber duration for a given absorbent will eventually injure or kill you. This is not a defect, plenty of capable units share it, but it removes any margin for sloppy packing or pushing consumables. You pre-breathe, you watch yourself for symptoms, you bail out at the first doubt. If you are the kind of diver who likes to stretch a fill, this platform will punish you for it.

The breathing hoses are fixed-length 15-inch rubber and cannot be cut. For a tall diver or someone with an unusual harness setup, that removes a tuning knob other units give you. You fit yourself to the hose, not the other way around.

The unit is fussy about power and service in ways that add cost and planning. Hollis bars rechargeables outright and insists on name-brand alkalines for life support, and recommends lithium once you are diving near freezing. The solenoid, the first-stage relief valves, and the high-pressure oxygen-clean components are not user-serviceable, so an accidental flood of the oxygen system means a trip to an authorized technician before the unit is safe again. Budget for annual service and oxygen-clean discipline as a standing cost, not an occasional one.

One more practical friction: the sensors are fragile and intolerant of shock. The manual notes a single three-foot drop can cut sensor output 25 to 100 percent, and recommends pulling the cells before any rough transport. For a South Florida diver loading and unloading a six-pack charter in chop, that means handling the head like glassware every time.

Compared to the JJ-CCR

The JJ-CCR is the unit most buyers cross-shop against this one, and the contrast is mostly philosophy. The JJ is a back-mount, one-configuration machine known for getting a new diver into clean horizontal trim quickly, with a fixed layout that leaves little to decide. The Prism 2 hands you choices the JJ does not: front or back counterlungs, and a user-packed radial scrubber instead of a pre-formed cartridge. That flexibility is a feature if you want to tune the unit to your diving and a burden if you would rather the manufacturer make those calls for you. Both run Shearwater electronics, so the handset experience is a wash. Pick the Prism 2 if you value configurability and want to own your scrubber packing. Pick the JJ if you want fewer decisions and a layout that is famously forgiving out of the box.

Who should buy this

Buy the Prism 2 if you are a committed tech or CCR diver who treats setup as part of the dive, not a chore to rush. It suits divers who already live in the Shearwater ecosystem, who want to choose their counterlung geometry, and who will hold the line on scrubber durations and annual service without being nagged. It is a strong fit for warm-water technical diving in the range it is rated for, and the dual-monitoring redundancy earns its keep on real deco dives.

Skip it if you want a rebreather that minimizes decisions, if you cannot commit to disciplined consumable management, or if you need a CO2 sensor in the loop to sleep at night. The Prism 2 is a capable, serviceable, configurable machine for a diver who wants to be the primary control system. It assumes your brain is the safety device, and it is honest about that from the first page of the manual.