Silent Running, Andy

Thank you for the post, questions, and testimonial!

In working on the re-engineering of the Prism, our first objective is to bring all the wonderful aspects of Peter’s Prism forward, with slight changes, to allow us to manufacturer the Prism more efficiently.

Our determination to do this with Peter’s Prism is in a large part based on input from divers like you who have a depth of experience in open circuit systems. Time and again we have been told of the durability of the Prism, and its ability to be field serviced so no dives are missed. Peter makes the excellent point about the oxygen sensor driven analog Secondary Display, that in the event of a loss of the system electronic oxygen set point control, the dive can continue as planned, just using manual control.

The Prism2 counterlungs will be attached just like the Prism counterlungs. There will be a Velcro gator and side release buckle at the top and the lower attachment will be another side release buckle that will attach to the harness waist strap, and the counterlungs will act as the shoulder strap. We will add a 2 inch D-ring on the outboard side of each counterlung at the middle of the length of the counterlung. We will retain the integral weight pocket.

Regarding bail out cylinder mounting; the envisioned configuration is to clip the valve to the D-ring on the outboard side of the counterlung and the lower attachment point is a D-ring mounted where the waist strap meets the backplate. From looking at Jill Heinerth’s video about side mounting on a rebreather, the Prism2 would be adaptable to that system too. We agree with you regarding drag, streamlining, and ease of use. Also comfortable, efficient, and enjoyable are all good words to use in safe dive equipment design.

We are going to change the waist strap to 2 inch webbing, with an optional cummerbund, and some pocket options including ditchable weight pockets, similar to the waist harness on the Hollis HTS. Based on input from Tech divers we will be using a crotch strap, rather than the thigh straps the original Prism uses, but the system will adapt to thigh straps. We are working on a design that will allow lots of customization. We should have this done in 6 weeks or so. We are also investigating an adapter to allow the use of tech metal backplates; we will have to revisit the counterlungs so they can be attached to the backplate’s shoulder straps.

We are working on tweaking the BC. Our concerns echo yours; we want great balance for horizontal trim, and a BC that is not going to get pinched when the Prism2 is placed on a bench in a vertical orientation for donning.

We like the analog Secondary Display too. We have a design effort underway to develop a battery powered digital Secondary Display, and we will continue to make the oxygen sensor powered analog Secondary Display that you like. It is indeed impressive to hear divers discuss an electronic mixed gas rebreather where a failure in the electronics is no big deal.

We are keeping an eye on servicing the Prism2 during our redesign efforts. We expect to deliver the Prism2 with most items user serviceable, and some items would require returning to a competent service facility, and some items would require returning to the factory. Most items can be swapped out; we will have spares readily available. Replacing some items, like the solenoid, would require access to the electronics housing, not something done casually. Calibration of the depth transducer would require specialized equipment, and would probably require returning the Prism2 scrubber head/electronics housing to the factory or specially set up service center.

We are planning on an optical data out port to transmit real time PPO2 to a dive computer. We are also planning for onboard logging of time, depth, and PPO2. We will have download of this data by USB, just like a dive computer with a PC application to save and display the data graphically and in analog mode. We do not want to disclose the algorithms we are considering at this time, one is new and revolutionary, one is established and well tested. It would not be too hard to make a black box that would convert the optical output PPO2 to a voltage value that would mimic an oxygen sensor.

We plan to have comfortable carrying handles on the top and bottom of the Prism2. One change from the Prism is where the cables plug in. We will use 90° fittings on the cables to attach to receptacles on the bottom of the electronics housing. This will let us rout the cables away from the carrying handle. With the exception of the cable to the Secondary Display the other cables will be well protected.

In regards to scrubber duration, the 255 minutes (4 hours, 15 minutes) was the average of several runs done by the NEDU in Panama City. The dives we done with an injection rate of 1.35 SLPM of CO2, a RMV of 40, water temperature of 40 F, at 60 FSW. The time given is the time it took to reach 0.50% CO2 SEV. Scrubber duration is very dependant on depth, water temperature, work load, and varies lot to lot of scrubber material. Shallow warm water where the diver is just observing marine life will yield the longest time, and deep cold dives swimming into a strong current will yield the shortest duration. The 245 minutes looks like a typo, thanks for pointing it out.

We have all of the injection molded components for the breathing loop in hand and are working with our suppliers to correct minor non-conformities in the components. The design package will be finished this week, which is delaying our schedule to build the first Prism2. With luck we will assemble a Prism2 in the later part of July or early August. Then the testing begins.

Hollis