Rebreather Evaluation and Review
Friday, January 16th, 2009Most of my tech diving buddies are now diving rebreathers, and I’ve been tempted by them for a couple of years now. You can make some serious dives with a lot less bulk and weight, the systems blend gas based on your partial pressure of oxygen, giving you an optimum blend at all depths. They are compact, making them easy to travel with, and because they use so much less gas than conventional scuba, the need for a large-scale gas blending operation on the boat or at home is virtually eliminated.
All these advantages, combined with the fact that they are just plain cool, finally convinced me to get one ordered and schedule the training. The only question that remained was which one to buy. I narrowed the choice down the three units.
The Inspiration by Ambient Pressure Diving
The PRISM Topaz by Steam Machines Incorporated
And the Megalodon by Inner Space Systems
I had direct experience with all of these units except the PRISM Topaz, but I had been hearing some convincing reports coming back from DEMA 2005, so I decided to include it in my product evaluation. Most of my friends are diving the Megalodon. They have all given it high praise, and recommended it strongly. For my part, I have always been very impressed with the quality of materials and workmanship on the Meg. The Inspiration was included mostly because of its wide distribution and the availability of zoomy electronics packages like the Hammer Head and Vision.
Since I was largely unable to find any literature comparing the benefits and drawbacks to these units, I needed to do a lot of research on each of them to make an educated decision on which one was right for my needs. With the hope that it will be useful to others. Remember that rebreathers are not right for all divers, and no single rebreather can meet the needs of all rebreather divers. I made my decision based on my needs and the type of diving I do.
The Inspiration
A LOT of people chose the Inspiration as the right rebreather for them. In fact, this unit has been in production for more than seven years and has, by far, the widest distribution of any rebreather available with somewhere between 4000 and 6000 units. It is also the only unit out there currently that carries a CE certification, making it a clear chose European divers. It was also the least expensive rebreather I evaluated, coming in at $5,200 for the basic package.
The unit, as far as I can tell, is top rate. It is rated to 300fsw, but I have personally seen divers exceed 400fsw using it, and those I know who dive them seem to like them. Among the features that people seem to enjoy most is the fully-automated calibration, whereby, at the touch of a button, the loop is flooded with oxygen and the unit is calibrated. Complaints tend to be few, but are generally centered around displays and harness system.
Ron over at tmishop has an excelent teardown of Kent Cedola ’s Inspiration.
Currently, you can get the inspiration directly from ADV in one of two configurations. The Inspiration Classic, which is the standard configuration that we are all used to, or the Inspiration Vision, which is the standard unit, with some very cool electronics.
Here is what you get with the Inspiration Clasic.
- 2 x 3 litre cylinders, one for oxygen, one for diluent (air or Trimix) with contents gauges for both.
- Two over-the-shoulder counterlung breathing bags - inhalation and exhalation.
- Mouthpiece and breathing loop hoses with hose-weights and built-in water-traps.
- A carbon dioxide Scrubber unit.
- A computerised Oxygen Controller system consisting of two micro-processor control units with digital displays and separate power supplies, three oxygen cell sensors and a solenoid oxygen injection valve.
- A specially designed harness and 16kg wings style Buoyancy Control Device with an Auto Air - emergency demand valve / jacket breathing valve / inflator - fitted.
- Manual diluent and oxygen feeds to the left and right counterlungs (ADV is an addon).
- There are two sizes of counterlungs, M or L and three sizes of harness, S, M, and L.
The inspiration Vision includes all of the above, with the following additions:
- Language Options
- Mixed Gas Deco
- Automatic Setpoint Switch
- Battery Status Indicator
- Head-Up Displays
- Software Upgradeable
- Logviewer Software
- APD Communicator Software and PC Interface
- Dive Timer
- Jacket BC
So, as you can see, the Inspiration Clasic is pretty much your basic ECCR, while the Vision electronics package adds some really nice bells and whistles, along with dive computer functionality. The downside to all this zoomy electronics is that it bumps the price up to nearly $10,000, which in my opinion, is far to much to pay for what you get.
Another option that gets you almost all of what is included in the Vision electronics is to purchase the Inspiration Classic, and upgrade to the Hammerhead electronics package from Juergensen Marine.
This system does a really good job of cleaning up all the wires inside the unit’s head, and replaces the standard Inspiration displays with two fully-functional dive computers to wear on your wrists. One of the greatest things about the hammerhead is that the software can calculate open and closed circuit deco, giving you the option of disconnecting the primary computer and using it as a standard OC dive computer. Not only do you get real-time P02 deco calculations while diving the rebreather, you get a nice, regular ol’ dive computer to boot… All for the low low price of only $3,000.
Had I chosen the Inspiration, the I would have gotten the hammerhead electronics along with it. Having real-time P02 deco is really nice, and the price is not too bad at $8,200 for the Inspiration Classic and the Hammerhead electronics.
I did not decide on the Inspiration, however, for the following reasons:
- I have never liked the shell. I have repeatedly seen divers break them, struggle with them, and generally hate life when dealing with them.
- The harness does not adapt well to slings. Divers do it all the time, but the system was clearly just not designed with the idea in mind that divers are going to sling 80 cf of bailout underneath their arms.
- There is no option for a metal backplate.
- There is no option to carry different sized tanks.
- The plastic used to make the scrubber is very soft and easily damaged.
- There is no standard HUD.
Again, the Inspiration is a nice unit, but it is mass-produced, and it looks it. It is simply not, in my opinion, designed to be flexible enough to easily accommodate the requirements of serious technical dives. This is not to say that divers are not making incredible dives on them… Just that it always seems to be a struggle to get the unit to do what they want it to.
The PRIZM
I had seen some photos of the PRISM coming back from DMEA, and it wasn’t too long before I started to hear some very positive things about it. In fact, one of the divers I admire most decided that the PRISM was the rebreather for him. Ergo, I decided that my rebreather evaluation would be incomplete without a good long look at the PRISM. Here are the PRISM specs, as well as a nice teardown of the unit.
PRISM stands for Peter Ready’s Incredible Steam Machine. Peter is, of course, the father of the PRISM, and head of Steam Machines Incorporated (SMI). Not only is this system incredibly well designed, it has two very nice features not found on either the Inspiration or the Meg. The first, of these, and the one that has everyone buzzing is the analog secondary display.
Sometimes called “the brick”, PRISM secondary gives a readout of battery voltage, as well as a PO2 reading from each sensor. “Big deal” you say. Every CCR on the market can do this, right? Wrong! The thing about the PRISM’s analog secondary that makes it so special is that it draws its power directly from the O2 sensors, and can continue to function even in the event of a total electronics failure. It is for this reason that the PRISM takes special, high output oxygen cells. Very very cool!
The second unique feature that the PRISM has to its credit is a radial scrubber. Unlike the more typical axial scrubbers in which the breathing gases move from top to bottom (or vise-versa) through the scrubber, the radial design moves the breathing gases from the middle to the outside (or vise-versa) through the absorbent.
TheRebreatherSite.nl is quick to tell us that “Only very complex tests show that the quantity of scrubber material, flow, form of the housing and many other factors determine the quality of a scrubber. Axial or Radial is not a general recipe for a good or bad scrubber.” Radial scrubbers do, however, have the added advantage of allowing moisture to condense on the much cooler inside of the scrubber bucket, thus, arguably keeping the O2 cells dry. Or at least that’s how the theory goes… It’s always hard to tell how well these theories translate to real-world experience.
The PRISM has some pretty nice other features as well. It is very light, which is nice if you have to hike to your dive sites. The solenoid exists outside of the breathing loop, meaning that it would not affect the PO2 of the breathing loop should it leak. The heads up display is by far the most well developed of any on the market, and there is an even cooler one as vaporware that will give a digital readout. The PRISM also has an optional shell if that is your kind of thing.
So what are the downsides? Well, in my mind, the fact that the analog secondary display relies on jeweled movement is a pretty serious problem. In the end, this is a millevolt meter that has been waterproofed and calibrated against the high-output O2 sensors to read PO2. As an electronics geek, I can testify that these millevolt meters break pretty easily when subjected to a shock. Even though I love the idea of being able to read my PO2 independently of the electronics, I worry that “the brick” just won’t stand up to the inevitable bumps and thumps on a dive boat. I also don’t like the little wheel it uses to select the individual sensors. I do a lot of diving in cold water, and I worry that this might be difficult to operate with thick gloves on.
The PRISM is made of plastic. Is this a bad thing? Most likely not, but I’m just not much of a plastic sort of guy. There is just something about nicely machined alluminium that makes me happy, and this rebreather doesn’t really have much of that going for it. It’s nicely machined, but it’s nicely machined plastic and to me, that’s a downside. Granted, there are some very good arguments for using plastic as a material. It makes the PRISM the lightest rebreather I evaluated, and plastic is wonderful about not corroding in salt water. Will the fact that the unit is plastic be cause for concern about the durability of the unit? Who knows?
The tanks are attached via velcro straps. This is really not a problem, but it’s certainly not as cool as the Tiger Gear hard mounts found on the Meg. From everything I’ve heard, the unit is very solid when put together, but I don’t think I would be able to strap aluminum 80’s into the thing.
Finally, and most importantly, there is something that bothers me about having only a heads up display and an analog secondary as instrumentation. Sure I can tell what the PO2 is by watching the HUD, and double check it against each individual sensor by toggling “the brick”, but I really want to be able to easily see each sensor’s readout on redundant digital displays. In my opinion, SMI has taken away from the usability of the unit in every day diving by making sure you can stay fully closed circuit even with a total electronics failure. It’s always a balance, and I certainly appreciate the fault tolerance, but I think they’ve planned a little too much for the worst possible case. This is, of course, all just conjecture, as I have never even dived the thing. It’s just how I imagine it would be.
So that’s my feelings on the PRISM Topaz. Remember, I have never even seen the unit, let alone dived it, so please comment if I have made any glaring errors.
The Meg
The Megalodon is made by Inner Space Systems, and is the brainchild of ISC owner and CEO Leon Scamahorn. I first got a chance to see the Megalodon on the Nautilus Explorer after a friend had bought one, and I was very impressed. It is a very serious looking unit and has a distinctively hand-made, one-off feel to it.
Unlike the other units I evaluated, the Meg is completely modular. There there are some standard configurations, but in the end, nearly everything is an optional addon to the basic envelope. It is built on the foundation of the outer housing, which is essentially an aluminum cylinder containing the standard axial scrubber, oxygen cells and electronics package. Two nice displays are attached to the head, as well as an optional HUD. Since the outer housing is constructed of aluminum, it is very rigid, giving you a number of options when it comes to attaching your oxygen and diluent bottles. The one I like best is the Tiger Gear setup, whitch provides a very elegant and tough mount.
The hoses, ADV and front-mounted counterlungs are all extremely well made, and the design on the unit gives it a very low profile. Leon spent 12 years with the Army Special Forces and it’s clear that he has built the unit with his military background in mind. The first thought that comes to mind when you see the Megalodon is that it is both incredibly rugged, and user friendly. The displays are large and easy to read, and apparently they tested the resiliency of the unit by dropping it from five feet onto a concrete floor. When a component broke, it was made stronger. When they were all done, the Meg was fine, but the concrete floor was broken. Did I mention that this unit is built to be tough?
The ISC website has a really nice breakdown of the Meg.
The list of things I like about the Megalodon is fairly long and detailed, but I’ll try to sum it up as best as I can:
- Solid construction
- High quality materials - Alluminum, ballistic nylon, acetal, etc.
- Water traps EVERYWHERE
- Corrosion resistant
- Easily readable handsets
- Low porfile
- No housing / shell nonsense
- Batteries sealed off from the breathing loop
- Modular design - Mount any cylinders, use any backplate / wing.
- Ability to use any scrubber you like - Megalodon, CisLunar, Extendair, and an SMI Prism.
There aren’t really many things I don’t like about the meg, but there are a few points I think might make it a little better.
- I wish it had a radial scrubber. While you can use the CisLunar or SMI Prism scrubbers, you have to purchase these seperately if you can find them.
- While the electronics package is great, it is only a loop controller. I wish the unit had the ability to do integrated deco calculations. This feature is coming in the next version of the software, but I would imagine that it will be a costly upgrade.
- I would like to see a slightly more readable HUD. It is only one LED that blinks codes for each sensor. This is fine once you get used to it, but the SMI Prism has a slightly better HUD in my opinion.
That’s about it. Like I said, these aren’t really complaints, but more of a wish list. The Meg is, after all, the unit I decided to get for myself.
The following are the additional options that I decided to get on my Meg:
- ADV (Automatic Diluent valve)
- HUD
- Mixed Gas Bypass - A must for TRIMIX, it provides the option to plumb in off-board gases
- Faber 20cf Steel bottles
- Stainless Steel back plate with continuous loop harness
- Drive Rite Aircel TREK wing
As I believe it will result in a system that runs with much less moisture, I have every intention of trying to find a CisLunar radial scrubber at some point. This is by far, the most advanced scrubber design ever seen in the world of rebreathers. For the time being, however, the standard ISC Axial scrubber should be just fine.
Conclusion
In the end, the Meg ended up winning the day. There are a lot of reasons for this. The Meg is an outstanding rebreather in just about every way, but perhaps the most compelling reason for my decision was the fact that most of the people I tech dive with regularly are using them. This is not to say that getting a unit simply because your friends are diving it is a good idea, but there is really something to be said for all members of a team using similar equipment.
After picking up my Meg and completing my training with Leon in Centrailia, WA last month, I continue to feel good about my decision. When he starts talking about the Meg, Leon sounds like a proud father, and the amount of thought and planning that has gone into every aspect of this outstanding rebreather becomes more and more evident each time I dive it. I am particularly impressed with the water traps in the “T” pieces and the drain valve in the exhalation counterlung. Assuming you aren’t doing summersaults, it seems virtually impossible for water to enter the scrubber canister.
I’ll be anxiously awaiting the Apecs 3 software which will have constant PO2 decompression software built in. Leon has established a relationship with deco guru Bill Hamilton, and word around the campfire is that the algorithm in Apecs 3 will be written by the man himself!
I’m still flying with clipped wings though because my VR3 does not do constant P02 deco. I have one of the original square VR3’s that came from OMS, and Delta P is telling me that there is no way to upgrade the code to do constant P02. That sounds a little fishy since I remember buying it with CCR constant P02 as an option. It kind of seems like someone is looking to sell another VR3. Weather I buy another VR3 or simply upgrade to Apecs 3 depends on the how much the Apecs 3 upgrade will cost. I can certainly see some benefit to having everything built into one nice package, but the redundancy you get from having a constant P02 VR3 hooked up to its own independent cell makes for some really nice fault tollerance.
I’m really quite happy with my Meg, and I’m really excited to start putting some hours on it. I thoroughly enjoyed Leon’s training program. I was able to meet some great new people, hang out with some old friends, see Ron, whom I had not seen in years, and meet a new dive buddy who lives near my home.
