Hollis Prism 2 CCR

[Lake_Tahoe_Diver]

Holis,

I am a current user of the Prism and I have one more request for a feature or add on for the Prism 2. What I will like to see is either a altitude adjusting feature in the set point software so we can calibrate correctly, or have a pressure pot that we can place the O2 senor in so we could increase to pressure to 1 ATM since the set point controller assumes when you press it you are at 1 ATM. So at 7000 feet a set point of 1.4 is more like 1.2 if you let the set point controller do the work since we are at .8 of an ATM.


I like the idea that you are thinking about a backplate add on, many of us are using backplates on the Prism and love it. There are few some nice examples of a compate plate that you bolt the head and strap scrubber bucket to, then attach it to a standard backplate like any other set of twins on another rebreather forum that a lot us of here visit also.

I look forward to seeing the new Prism 2 and seeing how it compares to the unit I have grown fond of over the years.

 

[sunnyboy]

Hollis,

Although I have only been diving a Prism for a year now, I love my unit and have some very definite comments on your post regarding the new Prism 2 and the direction you should pursue.

First and foremost, you should consider the rig a TECHNICAL rebreather and not bother with all the recreational BCD stuff. As soon as I got my Prism home, the BCD was completely removed and the DSS "Prism 6 bolt to 2 bolt adapter plate" was installed as well as their "Counterlung yoke adapter". This allowed me to ditch the BCD in favor of a stock backplate and wing (I use the Agir 38lb which is perfect for the Prism).

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.

This puzzles me. While much in the OC world can be of value to the rebreather diver, I would not necessarily seek out just OC advice.

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.

Please don't go this route. The counterlungs are NOT shoulder straps, and trying to make them do double duty is a less than optimal approach, IMO. My shoulder straps are provided by the stock backplate (single webbing design). The counterlungs attach at the top to the yoke adapter, and at the bottom I use the stock Prism web between the fastex on the bottom of the CL and have the harness waistband pass through. Since that opening is rather large, I have rubber innertube loops to reduce the opening thru which the waistband passes. Works great.

Under the counterlung d-rings (again DSS) are a perfect solution. Putting D-rings on the counterlungs will put stress on the counterlungs that is totally unnecessary. Let the harness do it's job, and let the counterlungs do their job - please.

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.

Again, please just let the counterlungs be counterlungs. Let the harness /backplate do it's job.

As for sidemount, once you have a harness/backplate, you can easily add sidemount to it, so there's no need to worry about it in the Prism 2 design (unless you want to do all this tomfoolery about the counterlungs and D-rings and such).

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.

Again - why not just ditch all this nonsense and provide a proper mount point (i.e. two bolts) for a backplate and wing of the owner's choice? You could supply one with the unit (most backplate/harnesses are pretty much the same from various vendors) and a good small (38lb) wing. (Whether you go donut or horseshoe is one of those "mine's better than your's debates anyway).

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.

AGAIN... a stock harness/backplate/wing will provide this without Hollis wasting time reinventing the wheel. This bit of the kit has pretty much been refined by now - just use something classic and proven.

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.

That is good news.

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.

I agree with a prior post - there is no reason the solenoid could not be user replaceable. The Prism currently uses molex connectors for the cells, so something similar could be inside the head for the solenoid.

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.

OK. Don't really care, but these type of options are common in most rebreathers now, so you have to offer them or risk being labeled "dinosaur". I prefer tables, a bottom timer and a brain, but others will have different desires and choices.

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.

Sounds OK. I have not had any problems with the cables or attachments, so I'm not sure this is really a big item, but if it improves routing without introducing a failure point, that's alright. Mind you, I've never had good luck with ANYTHING electronic and a 90 degree connector, but who knows - you might be the one to get that right. ;-)

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.

As long as you don't make major changes to the current radial scrubber or the technologies that keep the scrubber away from the small amounts of moister in the bucket, and still provide the duration, that's good.

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

Sounds good. Please post some pictures of a unit AFTER you have done the first dive or two on it. I'm looking forward to seeing the new unit.

ONE OTHER THING - it would be nice to offer the unit in two configurations - "ready to go" (that is, with wing, backplate and harness) and "almost ready to go" (no backplate, wing or harness but ready to attach to one of the purchaser's choice).

Cheers,

-S

 

[silent running]

This puzzles me. While much in the OC world can be of value to the rebreather diver, I would not necessarily seek out just OC advice.

Hi sb, as I said on RBW, given that his post was mostly a response to my earlier one, I'm pretty sure Hollis meant "a depth of CC experience", not "OC", as we had a prior conversation about my RB diving history, which is more extensive than my OC history.

Also, I think he said in the above post that there will be modularity to the Prism 2 harness to provide for traditional BP systems, such as the one you favor. He also said they will use standard 2 inch webbing for the waist and that the cumberbun will be an option and the unit will have a single crotch strap, no thigh straps like the SMI model. So, obviously they are listening to the tech divers who bought Prisms.

After taking my trimx class with a traditional web harness for the shoulders, I can't say I like the separate shoulder strap arrangement. I found that it was more complicated, less comfortable and required another person to help myself and even my instructors, get into it. The whole loop must be pushed up and behind your head when donning and I almost had my nose broken when I tried to do it by myself and that heavy brass ringed DSV came smashing down on my nose while doing the chicken wing to get into the web shoulder harness.

After trying 3 different harness setups, I have settled on something much like what Hollis is describing-2 inch waist webbing with CLs threaded through it and still functioning as the weight baring part of the harness. I had my velcro CL yoke sewn onto a DSS low profile composite harness plate. BO for me is side mount and more comfortable and much more streamlined than sling tanks. All that being said, I think carrying smaller-40 cuft-BO tanks sling style off of the CL mounted D-rings Hollis is proposing will be fine. Maybe steel 100's or 120's are too heavy above water for a CL attachment, but again I think side mounting is still the best way to rig BO, large or small. I can't really tell the difference btw a 40 and an 80 when I'm swimming, as there is much less drag.

With the CLs functioning as the shoulder straps/weight baring part of the harness, it may be less comfortable above water to attach large, heavy BO, but it is much easier to get into the harness to start with if all you have to do is slide in from underneath. This is why I like side mount BO best-easy to get into the unit and BO is stream-linned with no limits on how heavy the cylinders are.

But to each his own, though it still sounds like the Prism 2 will be much more easy to customize than before. -Andy

 

[Hollis]

Sunnyboy

Thanks for noting the OC which should have been CC !!

Lake_Tahoe_Diver

We will look into this and see what we can do to help out high altitude divers

Hollis

 

[Hollis]

Prism counterlung construction

We have gotten a lot of comments from folks regarding the counterlungs, the Prism’s harness and tech harnesses so I thought a little bit of information about the Prism2 counterlungs would be helpful.

Our first design goal in working with the Prism is to not loose the excellent performance Peter has designed in.

First and foremost we do not want to change the breathing characteristics of the Prism. The Prism did meet the Navy’s criteria and we think that is something to be proud of, Way To Go Peter!

Counterlungs are not just bags hanging in space that you swap gas with as you breathe.

The new method of counterlung evaluation that Dr. Dan Warkander (US Navy NEDU) presented at the DAN tech conference in Raleigh deals with 3 breathing factors that must be evaluated for closed circuit systems. Resistive effort is one; this is the difficulty of pushing or pulling gas in the breathing loop, the difference between a soda straw and a snorkel. Hydrostatic Loading is another; this is the relative difference between the pressure center of the diver’s lungs and the maximum and minimum pressure differentials when the counterlung is fully inflated and fully emptied. The last is Elastance; this refers to the change in shape of the counterlung as its volume changes during a breath.

Each of these 3 elements causes the diver to do work when breathing. You can have a mix of theses 3 kinds of work but at some point the diver will become fatigued just from the work needed to breathe. Lower work of breathing is a design objective.

In a normal swimming position the hydrostatic load of back mounted counterlungs produces negative lung loading, and chest mounted counterlungs produces positive lung loading. The hydrostatic load of over the shoulder counterlungs comes very close to reducing lung loading to zero. Less lung loading is less work to breathe.

Small diameter air passages have higher resistance to flow, or resistive effort. So do elbows, long tubes, flow direction mushroom valves, and thick scrubber beds. Using a sufficiently large diameter throughout the breathing loop, avoiding bends and elbows, using low durometer mushroom valves, and a radial scrubber all reduce resistive effort. Lower resistive effort is less work to breathe.

Elastance is related to hydrostatic load changes during breathing. A large flat counterlung (flat side down) would have lower elastance than a long narrow tube (tube vertical in the water column). Over the shoulder counterlungs seem to be a good shape tradeoff for low elastance. Lower elastance is less work to breathe.

If you look at the Prism counterlungs you will see a few features that are important.

First is that the counterlung is attached to a substrate made of two layers nylon cloth with a stiffener sandwiched between the fabric layers. This assembly is very strong. The Prism doesn’t really use the counterlungs as shoulder straps. When we attach items to the counterlungs we actually attach them to this under layer. This layer also helps keep the Prism counterlungs in an optimal shape.

Next are the 3 side release buckles. These hold the counterlungs down and keep the counterlungs near the diver’s lungs, not floating around or shifting when the diver changes position. This does require the use of thigh straps of a crotch strap to hold the Prism down on the diver.

We have discussed making counterlungs that would adapt to a tech harness by some form of attachment to the shoulder straps. We could slap on some Velcro and be done with it, but that may not do the job well. We need to be certain that once adapted for attachment to a tech harness shoulder straps the counterlungs will continue to work as intended. Remember the counterlung is not just a gas bag floating in space.

Our current time line has Prism2 initial production in late July or early August. This will be a small batch to shake out material issues, assembly requirements, in process testing, and final qualification testing for production units. These units will be used for unmanned testing in our hyperbaric lab and for some open water evaluation dives. Once we are satisfied that the rigs work as intended we will enlarge the user base to include some of the folks who have been advising us all long in this project.

Once we are sure we have reached our design objectives we will begin investigating adapting the design to tech plates and harnesses, while retaining the functionality we have worked to preserve.

We appreciate all the input we have gotten from the boards and from CC divers who have told us of their likes, dislikes, and wants. We think we have a great product in the making. We all want one for ourselves. It is difficult to bring a product of this complexity to market, safely.

Hollis

 

[sunnyboy]

Hollis,

Great post. I think the PRISM counterlungs are absolutely fantastic. Sounds like you are doing good things with the design.

As I said, my biggest suggestion is to leave the recreational BCD concept behind. I personally still prefer the single webbing "Hog" harness over anything else I've used. I'm still not sure I'm convinced about using the counterlungs (or the backing) as harness straps - if only because it negates the "single webbing harness" concept, but I'll wait until I see the finished unit.

Mike - I think sidemount is great for bailout - I'm still refining mine. Maybe Hollis could offer sidemount as an option for the new Prism.

Cheers,

-S

 

[Hollis Gear Nick]

Hi All,

Thanks again to everyone for all the comments and suggestions. We are looking forward to bringing the final product to market.

Regards,

 

[sunnyboy]

Hi All,

Thanks again to everyone for all the comments and suggestions. We are looking forward to bringing the final product to market.

Regards,

So what do we have to do to participate in the trials of the new Prism down the road?



-S

 

[Hollis Gear Nick]

So what do we have to do to participate in the trials of the new Prism down the road?



-S

Hi Sunnyboy,

For a complete list of Hollis dealers in your area that will be carrying the new Prism 2, please visit our website. They will be able to provide you with any info on a demo/first look at this unit.

Thanks,

 

[sunnyboy]

Hi Sunnyboy,

For a complete list of Hollis dealers in your area that will be carrying the new Prism 2, please visit our website. They will be able to provide you with any info on a demo/first look at this unit.

Thanks,

Actually, we had this conversation (dealers) once before. You don't have anyone in my area. In fact, you have no-one yet outside Ontario according to your website.

Although is is possible to purchase from the USA, it is essentially "mail order" and has it's own difficulties.

I would really like to see a dealer on Vancouver Island but I doubt that's in the cards.

Cheers,

-Richard