Prism II or Se7en?

[RainPilot]

Hey Ken. Out of curiosity, what would you see those circumstances being?

Would like to avoid some of those user errors

 

[kensuf]

Telling your computer you have one % ean for DIL and in reality having another.

 

[RainPilot]

My unit analyses the dil during predive and will fail the test if it's more than a percent out. IF both the cells have failed in the exact same way, but then I would also have to have a corresponding impure O2 blend.

If the He percentage is off in the dil then it has no way of knowing.

 

[NAND]

...as a north European I shouldnt say it, but: Go for the Hollis

Personally, I cant deal with the se7en being a pure eCCR denying you from manual O2 addition and being delivered with a nasty looking paddle which indicates errors as numerical codes. Buddies out with me on dives were quite often repeating their linearisation tests until their O2 dropped so badly that the standard reply I got used to was: "Rather short dive for me, no deco this time- ok?", not mentioning those with CO2 Sensor fitted consuming their DIL OC upon descent to 5m just realizing the sensor may be moist. Proper dive planning was really often more luck than reliability...

I'm not a Hollis fan either (no experience with the Prism but bad experiences with my GF missing dives on an Explorer frequently) but the Prism comes with a Petrel2 on it, a unit which I concider the best CCR Setpoint controller on the market. Mainstream- yes. It is by reason you find Shearwater on almost all modern CCR.

Never dove a Prism2 myself, but looking through the Manual it seems perfectly straight forward. I would compare it to a JJ, rEvo etc. in terms of diving procedures.

(To be fair I have to say to be neither licensed for both units, speaking from general eCCR and mCCR experience)





https://www.hollis.com/media/wysiwyg/HO/manuals/Prism2_Manual_12-4072_rev7_12-12-13.pdf

 

[guruboy]

You can add manual valves to the lungs on the se7en.

As far as linearity test, was it their choice to repeat it so many times or was the test failing repeatedly? If the test keeps failing, I don't know that I would still dive.

I read the se7en manual and it does it on the surface and then again in the water (you can't get above 1.0 on the surface). If it fails in the water you can still dive it with the understanding that any reading above 1.0 cannot be trusted so the setpoint is capped to 1.0.

 

[688ClassRebreather]

If you use the m28 you cant control set point but you can change your OC gas if you switch to a bailout bottle. But I guess that's more money to spend.

I was reading a se7en faq and it will let you keep diving even if you get bent. What other kind of lock out would there be besides failing a system test? Why would you dive if a safety test fails?

Both Prism 2 and Se7en use the same O2 sensor currently.

When diving the Se7en with the M28, you can control the setpoint. If you are planning to dive only within recreational limits I am not sure why you would want to, but you can. I teach the Se7en at Hawaii Scuba University and adjust the setpoint during dives frequently.

 

[688ClassRebreather]

@kensuf I just saw a Pathfinder going for $3k as well which is a nifty unit.

@guruboy the ability to use solid state O2 sensors is already available for the Prism. You have to buy the CPOD and M28 and it can monitor the sensors. It can't drive the solenoids, but you may find that you don't want to blindly trust the computer to maintain your setpoint in favor of a hCCR upgrade, or just run the unit manually with the solenoid as a parachute. The cost of upgrading to the M28 with the SS sensors is going to be quite steep. As it stands, we don't have a date or cost to do that upgrade, but I would expect the end of this year at the earliest but likely early 2018, and an upgrade cost of at least $4k, likely $5k. It will require being sent back to the factory or the service centers for the upgrade. It requires a new O2 board in the head itself, it's not something you can just drop right into the head in place of the current cells. The new board should be backwards compatible with the galvanic cells, but it still requires a new board. M28 will be required as well, so it's not going to be a cheap upgrade.
Currently that service center in the US is Jeurgensen Marine who has not exactly made a lot of people warm and fuzzy with their service time, cost, and politeness. It is enough for me to avoid that unit alone.

The Prism II currently uses the Shearwater DiveCAN which is arguably the best eCCR electronics set on the market. You cited as not being able to support the SSS which is not true. The DiveCAN is a digital system and is able to accept a myriad of different upgrades. Those boards need to be designed by Shearwater and the CCR manufacturers no differently than the existing O2 boards. Poseidon plans on releasing these sensors to the wild after they have the CPOD's out and all of the Se7en's upgraded, so expect early 2019 before they're available to the public, and depending on how this Huish acquisition goes, we'll see how quickly they respond to getting an upgrade path, but 2019 is realistic for an option to go to SSS for most of the DiveCAN rebreathers on the market. Can't guarantee, but it's likely to happen for most of the units in a pretty timely manner provided that all of the early testing goes as well as we are hoping.


now, all of that said. What are your answers to Ken's questions? Why do you need or want a rebreather?

I agree with your comment about service. Turn around times are measured in weeks or months.

 

[tphelps]

Prism II or Se7en Rec package?
For use in mostly recreational diving in the near future.

A lot of good comments so far. Allow me to offer my input as both a Prism2 Instructor and Poseidon Se7en diver.

As @kensuf mentioned, the first questions in the CCR discussion you should have is WHY rebreather in the first place and what is your end goal with them? Your motives are shared by many; it offers a new challenging platform that gives new interest in diving.

In terms of end goals, both can take you as far as you want. I use my Prism2 on mesophotic dives with the California Academy of Sciences and we collaborate with Bishop Museum (including aforementioned Rich Pyle) who uses Se7ens. Collectively we are taking the units beyond the ranges of most, so you have done a great job of narrowing down your CCR selection to two very scalable units.

Personally I believe the electronics has too much impetus on the Se7en. Yes you can get manual ads but you are then paying more for something that comes standard with the P2. During my MKVI and Se7en training, I encountered glitches and was taught workarounds we had to do for the Poseidon units during the automated safety check. The frequency of these has gone down but I still hear about them from my friends that dive Poseidons. Although more time consuming, I feel more comfortable using the manual checklist when diving my P2. I am a big fan of Poseidon's sensor validation, and am very interested to see how the solid state sensor goes. It definitely will not be a cheap upgrade, similar to @tbone1004, I heard it would be about a $3,000 upgrade. I do not see myself investing in this until maybe the price comes down significantly. With annual replacement, we have had very few sensor issues with the galvanic cells considering the hundreds of hours they last through.

I am a fan of the cost savings we have on packing our own scrubbers with the P2. The downside is the Prism has a very tedious packing design, wish it was spring loaded like the Inspiration or others that have. The counter lung drains on the Prism are superior to that of the Poseidon, which is great for loop recovery if you had to. I am a fan of options and flexibility the M28 provides but keep in mind it is a very new computer. Just had a friend that had his cut out on him at 270fsw, no flood, it just glitched and shut itself off. Compare to the Petrel 2 that has been tried and tested, there is a reason why Shearwater has the best dive computers on the market.

Another key point that has been neglected so far is the work of breathing (WOB). Between the shorter hose lengths, over the shoulder counter lungs, and radial scrubber (which is far better than the axial design of the Poseidon) the Prism2 has arguably the best WOB on the market (especially when you add helium).

The standard counter lung sizes for both units are far too large, no one has that large of tidal volume! We upgraded to the smaller 2.5L lungs which allows for easier loop volume control, set point management, and faster dil flushes. I do not know if Poseidon offers a smaller lung option.

I do like the valve up cylinder orientation on the Poseidon. It makes valve drills and bubble checks more consistent from OC to CC, and is easier to detect/diagnosis leaks as opposed to the valves down on the P2.

In terms of bailout valve (BOV), Poseidon takes the cake, hands down. I am impressed by the cheap construction of the P2 BOV and have had more than a few issues with it free flowing. The vibrating mouthpiece and low profile HUD on the Se7en is fantastic. The new HUD on the P2 uses a modified Smither's Code which is far superior to the old HUD. Unfortunately the water contacts are very sensitive, constantly turning the HUD on which is annoying.

In terms of battery, I am not a fan of Poseidons'. The requirement of having to spend hundreds to dollars for a deeper battery would be frustrating for me. You do not have that issue with the Shearwater on the Prism2. And if your battery dies, it costs hundreds to replace. The P2 runs on two 9Vs, a 3.6V Saft, and a AA in the controller - all of which are far cheaper and easier to replace.

Take Away Message:
Every unit has its pros and cons, a "perfect rebreather" does not exist. What led me to invest in the P2 over my other unit certifications was: 1) superior WOB 2) Shearwater electronics 3) less electronics impetus (as opposed to the Poseidon) 4) accessory options (small counter lungs, back mount counter lungs, full face mask, and versatile head that allowed for multiple controllers). I want to emphasize the electronics again. It's more valuable skill to use a manual checklist as it will make you a more conscientious CCR diver, not relying on the machine to do all the checks for you. The ability to fly the unit manually will also make you a safer CCR diver. The P2 has been a reliable and dependable unit for me in extreme exposures, which is why I became an instructor for it.

After you have decided on which unit, my next recommendation would be to carefully select an instructor. Especially for rebreathers, I would not recommend a "cheap and quick" class. Find an instructor that actively dives the unit. And as @kensuf mentioned, I strongly recommend Mastering Rebreathers. Jeff Bozanic was my CCR instructor, his book is phenomenal. Best of luck in your decision and feel free to PM me if you have any questions.

 

[NAND]

@tphelps - Best advice I read for a while (as well better than my own). Would love you to be my instructor one day!

 

[Doc Ben]

As an experienced OC diver wanting to get rebreather trained, I appreciate the comments from those with experience. A quick true story...I Googled "rebreather training" and got Rusty Berry's Scuba Schools of America webpage and it stated Poseidon training for only $750...Rebreather Diver Training. But when he called me, he said the Poseidon was electronically unreliable and I should use the Prism 2 as it could be controlled manually. So why not advertise Prism 2 training and delete the Poseidon reference?? Well, apparently Rusty has a bad reputation according to this SB. Is this another "bait-and-switch" tactic?? Rusty wanted my credit card for an over $12,000 package deal after only talking with me for less than 30 minutes! So now I am very cautious as to what unit I will buy and with whom I will train. In San Diego, there appears to be few choices...A PADI Instructor wanting to use the Poseidon OR a NAUI Instructor using the Prism 2. Any advice?