Rebreather: Decisions, decisions!!!

[emeraldvideo]

Hi everybody! I'm a new member of this forum. I'm in the market for a rebreather, and I found this site while trying to educate myself. A little background...I'm an avid cold-water diver here in Vancouver, British Columbia. I have 400+ O/C dives, mostly cold-water (I spent eight months in Cozumel). Last summer I managed to buy myself a digital video setup, so that's my main focus. Which leads me to the rebreather...

I'm drawn to rebreather diving because of the silence, the warm moist air, and the extended bottom times. I like the idea of being able to lie in wait for the video opportunity to present itself eg. sea lions gliding through kelp forests.

Here are the three contenders so far:Inspiration, RB80 or Dolphin. (There's a local guy making one called the KISS, but I'm not sure....) What I understand about these units:

Inspiration: constant PO2 nitrox/trimix CCR
pros: -best mix at all depths
-zero bubbles (except ascents)
-CE approved, diver tested
cons: -electronics + saltwater = potential disaster

RB80: Nitrox or trimix SCR
pros: -no electronics
-ideal gas extension 10:1
-huge scrubber
-mechanical alarms (breathing resistance)
cons: -training only by GUE (could be great but pricey and limited course offerings esp. in my area)
-same deco obligations as O/C

Dolphin: Nitrox SCR
pros: -no electronics
-very popular and affordable
-Draeger has been building rebreathers since early 1900's
cons: -Nitrox only (I've heard of people modifying to CCR trimix, but frankly this scares me!)
-therefore, limited range
-no warning of nozzle failure (PO2 monitor?)

I would really appreciate any suggestions or comments that could help me make this decision. I'm about to invest an awful lot of money, so I obviously want to make the most informed decision possible. Am I crazy for considering rebreathers...are they impossible to travel with? Do I have to dive on exclusive RB charters? Also, any suggestions as to RB/Computer combinations would be appreciated.

Thanks everybody!

 

[caveseeker7]

Welcome to the board.
I'm not sure how much you have read about RBs, but on several threads here on the board you'll find books and websites you should go through as they'll help your decision.
The 3 RBs contending are vastly different from each other in the way they operate. Hence very different pros, cons and limits. The first thing you ought to consider is your needs. So I'm going to start on the low end and work my way up with some thoughts:

Dolphin: No electronics is only partly a pro. There is no way to monitor the mix you're actually breathing without them. If you decide on the Dolphin I strongly recommend to get good O2 monitoring. Those come in two forms: An O2 monitor such as Dräger's Oxygauge, or a computer that gets info from an O2 cell, displays it as well as calculates NDL and deco with it. Pretty much made for the Drägers is the Uwatec Air XO2 with Oxy2 (the dual O2 cell sensor) and the DeltaP VR3 with SCR link. The Oxygauge gets plugged into a breathing bag that has the plugs receptor build in and has one fuel cell. The VR3 has the same set-up, but as mentioned is a full featured computer (that can be upgraded from Nitrox to Trimix and is also available with an Inspiration CCR link, calculates both FO2 and PO2 as needed-up to ten mixes). The Air XO2 can also be used OC, with or without Uwatec's wireless pressure sender. The Oxy2 is also wireless. Very neat, but it might get interference from strobes is you use those. Anyway, as the actual mix in the bag differs with your O2 consumption, you should really have a way to monitor it. First rule of RB diving: ALWAYS KNOW WHAT YOU'RE BREATHING ! Can't be said often enough. Even if waiting is what you mostly do, going against a swift current or chasing after marine life (or away from it) will happen sooner or later ... . That and the supersonic nozzle are the best two arguments against the Dolphin, the latter has to be perfectly clean to work as designed. On the plus side I put availability, there are plenty of places to get trained, parts, supplies and even rental units. That might eliminate the need to travel with the RB. Then again, the Dolphin is pretty small and light. Just need to make sure they have Nitrox and a bailout tank at your destination. Or get an H-valve, so you can hook-up a bailout demand valve on the main tank ... or better yet both. If you go past 130ft/40m, the stock Dolphin is out. If you stay within the recreational limits the Dolphin should work fine for what filming. Not quite as quite as a CCR, SCRs should get you closer to marine life, and the warm, moist gas will help as much as it does from a CCR. Training is shorter and less expensive, the unit is also the least expensive of the three. Using it is less involved as either of the other units. Limits are lower than either of those two, too.

RB80: Awesome rig with such an extreme (cave exploration) record ... wouldn't mind one of those. But price, size and weight is up there with CCRs (the Prism is smaller, lighter, less expensive ... ). The passive addition design is better than the active as the mix is more stable, it does have the increasing breathin resistance with depleting gas supply, and is more gas efficient. Scubber size I don't know, 4hrs is all I need per day, but that's just me. If you plan 8hr dives I'm sure it comes in handy ... . But the price is too high for me to justify. Also, neither the hardware to mount and hook-up tanks nor a bc or means to hook-up a diver (you) is part of the package. By the time you added that, training and an O2 monitor you probably spend about 12 grand (US). Add travel expenses to FL to get the trainig ... or Hawaii. There are a couple of IANTD insructors for the RB80, one of them in HI . Last time I checked GUE's website they had two RB80 instructors, so there should be about half a dozen worldwide. Parts/service or the unit I don't know about ... . At least you can change gases with the standard switch block, that solves most deco problems and depth restrictions. Also the DSV, while huge, offers OC-bailout. A feature upgrade I strongly recommend for any RB, there are several good ones available for both Dolphin and Inspiration (Bob's DSV is my favorite). Gas extension, by the way, ought to be 8:1. As this unit is strictly DIR you will not need a dive computer, that safes you about two grand.

Inspiration: It's my first choice. It just offers more than any SCR, for a reasonable price (for dives up to 2hrs the upcoming Evolution should be great as it's a smaller unit). Too many people go from SCR to CCR, I have yet to meet someone who went the other way... . Good availability of units, parts and training, extensive track record (not perfect, but at least the info is there), good support from the factory (and users), plenty of parts to upgrade and customize the unit as needed (same goes for the Dolphin, too). Very probably the best allround CCR off the shelf. As I mentioned above, the VR3 works well with it, likely the most used computer with the Inspiration. Can either be used on- or offline. The same goes for the HS Explorer, also a 10Gas FO2/PO2 Nitrox/Trimix computer that is now available with a RB link. APD offers the Buddy Nexus, a Nitrox FO2/PO2 computer for use with their RB. Go with either VR3 or Explorer with the RB link for online O2 monitoring and calculation, another source to know what you're breathing. And on a CCR you really need to pay a lot of attention to the unit and the mix you're breathing. (The wristmounted computers help here as they will be only a glance away once you hold your camera - the Inspiration's displays need a hand to pick them up. Although I saw one diver on an early unit with longer cables velroing them next to the monitor of the camera he carried on a 'short leash' around his neck).

You need to habe your camera skills down. You need to get your RB skills down. Don't even think about taking your camera anytime soon with your RB, no matter how tempting it is. Especially with a CCR. Take a lot of time to get aquainted with your rig so you know it inside out in any situation.

Stefan

 

[bill harvey]

What are the prices on these three units?

 

[caveseeker7]

... are about:
Dolphin - about $3600, including weight-integrated bcd and inflator-mounted bailout dv (both by the company that makes them for the Inspiration, too, AP Valves) and 40%, 50% and 60% jet nozzles and lowmeter. Not including tanks (4 or 5 ltr. steel), bailout tank (is needed as the bailout 2nd can't be used on the Dräger 1st stage) nor the 32% jet or O2 monitor.

RB80 - about $9000 for the RB only, including above mentioned integrated OC/DSV (OC 2nd stage bailout switchover mouthpiece) and gas switchblock. Not included is the frame, manifold and hardware to mount tanks, bcd (supposed to be used with (Halcyon) bp and wing) or O2 monitor.

Inspiration - $6995 (according to Silent Diving Systems, the new US importer :upset: that just went up in the tune of about $500 and includes some kind of service contract ... no clue what that's supposed to be) So far the unit was complete with 20cuft OMS tanks, APV bcd & bailout 2nd, just about everything included but the certification and a computer. Hope that stays the same.

 

[padiscubapro]

Personally don't like SCRs and wouldn't dive any rebreather where gas composition monitoring isn't available.. there is no such thing as a failproof design although the RB80 for an SCR comes the closest.. It does have one potential failure mode (not likely though) that can give an unbreathable mix without warning.. The biggest drawback here is the high breathing resistance..

The only ccr unit out there that can be truely called a production unit.. Its not without its flaws but the support is good and its the mostlikely unit (other than the drager scr) that you will see in your travels.

A unit that I would keep my eye on is the megladon.. its not a real production unit yet but leon has shipped some units and the quality level is high and has some nice ideas incorporated into them.

as a student you are probably still in a preferred range of experience for an instructor to teach.. You are not too new being unconfortable in the water and not too experienced where you have too many bad habits to break you of..

there has been a price increase on the inspiration as noted in an earlier message (I prefer to sell it wih a larger wing than the unit that was quoted earlier)

Regardless of what rebreather you decide to choose.. You are starting from scratch again.. a new diver.. your prior experience means nothing on the new unit..

I'll second an opinion voiced earlier.. I know many people that went from scrs to CCR but none that have gone the other way.. Once the person becomes confortable on a CCR there is no turning back... SCR diving is much closer to OC diving than to CCR diving

 

[db8us]

padiscubapro once bubbled...
Personally don't like SCRs and wouldn't dive any rebreather where gas composition monitoring isn't available.. there is no such thing as a failproof design although the RB80 for an SCR comes the closest.. It does have one potential failure mode (not likely though) that can give an unbreathable mix without warning.. The biggest drawback here is the high breathing resistance..

Hi,

i would not say the RB80 has a high breathing-resistance.
After 15 hours i still had no urge to switch to OC during deco !

To the "higher resistance" when running out of gas. That is also not exaclty the way it is. If you run OOG on a constant-volume SCR the volume gets smaller every breath, the resistance does not change.

What potential failure-mode do you mean ?

Michael

 

[padiscubapro]

db8us once bubbled...


Hi,

i would not say the RB80 has a high breathing-resistance.
After 15 hours i still had no urge to switch to OC during deco !

To the "higher resistance" when running out of gas. That is also not exaclty the way it is. If you run OOG on a constant-volume SCR the volume gets smaller every breath, the resistance does not change.

What potential failure-mode do you mean ?

Michael

A gas leak between the two chambers.. You can potentially get a hypoxic mix and it probably wouldn't be detected in predive checks.. its not a very likely scenario but neither is getting hit by lightning...Why rishk it when simple solutions are available either by integrated dive computers (explorer and VR3), oxygage or a simple panel meter bases unit like Mike m@ www.ppo2.com
I think a simple PO2 monitor is in order (also if you look at Navy tests on the same types of units) breathing rate does effect the loop composition but not to an enormous degree..
I saw a Navy report form not too long ago testing SCR like the rb80 in design (but not the RB 80) it suggested the PO2 consistency was acceptable and with predicted variations (its not as close as you think but its still pretty stable) but the breathing resistancy was too high.. The report was written by Nukols...(not sure of spelling)

What you call high breathing resistance is debatable.. at shallow depths most rebreathers breath well as gas density goes up so does the breathing resistance.. a 4 times increase in gas density results in about 2 times the breathing resistance.. so the higher the initial resistance the greater the effect will be at depth which in turn increases the risk of hypercapnia. most DIR people avoid this because they switch to helium pretty shallow. switching to a 50% helium mix degreases breathing resistance by about 25%.

Don't get picky with the numbers.. I don't feel like going through the calculations to give exact results... they are close enough for the intended point and are in the ballpark and besides the packing density of the scrubber will also change this.

Most people don't notice relatively small increases in exhalation resistance(but you do get effected) but do notice increase in inhalation resistance.

A split OTS counterlung will always give better inhalation reistance in the normal diving position with slightly higher exhalation resistance, the opposite is true for back mounted counterlungs..

in an inverted position back down/stomach up, most ots systems will only notice a small change since they have gas on both sides of them..., back mounted counterlungs will typically get chipmunk cheeks.. since all the gas wants to get to the highest point.

 

[db8us]

a Split-over-the-shoulders-CL i would not like.
I never saw a clean configuration so far.

To the failure mode:
Yes, if you would have a "shunt" between the bellows tahts right, but you would immediatly hear the unit "not venting" and therefore also "not injecting" at least as long as you do not use an Aquazepp (one of the reasons why they are crap).

I used to to the first hundred hours with an Oxygauge and also on some longer dives, but the electronics either flooded or the sensors gave up after a while.
While they were functioning the reading was as expected.

A VR3 and other computers i do not need, Oxygauges we have in the corner and we use them to visualize drop-speed during
Rebreather-weekends were we "sharpen" our people.
We plug in a hypoxic mix and they can see the pO2 drop.

But on an exploration dive who should watch the Displays every Minute like suggtested for the BI ? This would slow us down dramatically and we have to be focused on the buddy and the job(cave).

I never saw any measurements, so my statement about the WOB was only from my feelings and that is all i can say.
If one would say the RB80 breathes bad every Ray and Dolphin i would subscribe as "undiveable".

The best position however for the RB80 is "scooter-position", so if you are fully vertical it is not perfect. But still you can breath it.
Also when head down...
But we (the DIR-dudes) are horizontal almost anytime anyway


There is one more "theoretical-caution" with the RB80:
When going up slowly and steadily the volume might expand and so the unit will not vent and therefore not inject.
Due to the pO2 dropping anyway this might be a problem.
But again:
Who is not doing Deep-Stops should not use a RB80.
Who does not know this and act accordingly has no business using an Rb80 (or any unit IMHO).

So these problems are somehow theoretical. This is like isobaric counterdiffusion. It exists, but plays no role in our way of diving.

By the way we check the inner counterlung for overpressure and underpressure prior to every dive !

Michael

 

[padiscubapro]

I don't personally like the drager products and definately wouldn't dive one without PO2 monitoring, sonic orifices can clog too easily..

I also agree on the ascent its a potential issue, but unless the person is trying to end the dive before a deco obligation due to some issue it is a remote possibility..

If an SCR was acceptable to me it would be something like the RB-80.. I wouldn't pay that much for an SCR though..

I much prefer the constant PO2.. if you can multilevel a dive the deco savings are incredible..

for photography the RB-80 sytle may be too noisy for some critters, and a CCR or ughh! a mass flow unit may be necessary..

Spli OTS definately aren't the cleanest solution but they do offer the best breathing performance.. Its all a matter of tradeoffs..

 

[db8us]

I much prefer the constant PO2.. if you can multilevel a dive the deco savings are incredible..

So far everytime i had been in the same caves with constant-po2-dudes there bootom-time was substantially shorter, they went maybe a 10th of the distance and yet i was already completely undressed and packed when they came out.

I never did any constant-pO2 decodive, but i think it might be related to trusting the stupid algorithms in the dive-computers.

So it might have been the users and not the units. I can not comment on that.

Michael