Keeping in mind that I did not have access to any TRIMIX I decided that I would not go much deeper than 155 feet, which is the point on rebreathers where you really should start using Helium in your mix. This is not only to buffer the narcosis, but because going deeper than 155 using air diluent at a 1.3 setpoint causes you to actually incur more decompression obligation than if you were simply breathing straight air.

The other thing to remember when doing deeper rebreather dives using air diluent is that the effects of narcosis can be much more troubling than when diving open circuit. When you are breathing off a tank, you feel a bit of narcosis in your head and you know exactly what it is and, assuming you have acclimated yourself to it slowly and over progressively deeper dives, how to deal with it. You can accept the narcosis and go on about your dive.

On a rebreather, however, you are breathing off a recirculating loop which is monitored by oxygen sensors. You constantly check the status of this loop and you depend on the sensors to give you accurate information, quite literally, with your life. Should you have too little or too much oxygen in your loop, your body will give you very little warning before you either fall asleep or go into convulsions. For this reason, you are not only constantly monitoring your loop, but also how you are feeling. In deep water, it becomes easy to ask yourself if the narcosis you think you are feeling might actually be lightheadedness from a C02 breakthrough or impending hypoxia.

Anyhow, to make a long story short, I really wished I had some helium, but I didn’t, so I was stuck going not much deeper then 155. On the first dive of the day, Rich and I went down the shotline, snaked around the outside of the canyon wall, and headed down the gentle-sloping topography. As we descended, there were a lot of little rock platforms that came up about 10 feet off the sea floor. We made our way from one of these to the next until we finally found ourselves at the top of one in exactly 150 feet. We hung out for a while, looking at several white-tip reef sharks, but finally decided to head back up into shallower water. We met up with our friends at about 80 feet where we all started making our way back to the line. The entire dive lasted 50 minuets and it was the deepest dive I had done on my Meg to date.

The second dive of the day was supposed to be at a site called “The Boiler“, a stone pillar jutting up from the seabed, and peaking just slightly below the surface of the water. It is an extremely exposed site, and it became clear on the boat ride out that there was no way we would be diving it. At one point the skiff broke loose from the Nautilus and the crew had to go rescue it. I’m also sad to report that a very nice camera took a digger because of the high seas, breaking the dome and bending the lens. Overall, it was a very bad boat ride!

Cutting our losses, we returned to the Canyon, which was in fairly protected waters and still very divable. The Nautilus anchored directly at the dive site, so we could splash right off the back and stay down for as long as we liked. The divemasters had also rigged a trapeze underneath the Nautilus at about 30 feet, allowing divers to pull themselves from the dive deck on the stern to the main anchor line on the bow. I made my way down the line, and as before I rounded the wall and headed down the bottom, making my way from platform to platform. On this dive, I decided to go alone and stay down a little longer than before. I stopped when I arrived at 160 feet, and stayed there for about 5 minuets. As before I saw some sharks, but little else, and finally decided to head back. I saw a few other divers on my way back, but not wanting to get into too much deco, I decided to leisurely make my way back to the anchor and complete my decompression.

All told, I stayed down for an hour and decompressed for 20 minuets, adding about 10 extra on pure oxygen just for safety. Many of the other divers decided to do one more dive before we pulled anchor and headed back to Cabo, but I was happy to stay dry. My last dive had been great fun, and I thought it a great way to say goodbye to the Revillagigedo Archipelago.

That evening, we began the long, 27 hour journey back. The next day we spent cleaning gear, settling tabs, sharing pictures and videos and generally chatting about a great trip. The ocean was quite rough, so I spent a great deal of the ride back with a twinge of seasickness, but nothing too bad. We finally arrived in Cabo San Lucas at about 10:30 PM. We all wanted to get off the boat pretty badly, so a bunch of us headed out to Cabo Wabo to see if we could find Sammy Hagar, or at least some burritos and tequila. Luckily we found both, but we headed Sten’s warnings and stayed away from the police and the people looking to make “new friends”. Cabo really is just a big old party.

We made our way back to the boat by midnight, and headed out to the airport the next day at 9:00AM and just like that the trip was over. It was wonderful diving and wonderful people. I highly recommend the Socorro Islands to anyone who loves diving, and loves large sea creatures!

So it was that I found myself on open circuit SCUBA gear again that morning, which was just as well because I was tired and groggy thru-out the entire first dive and there was a LOT of current. It’s hard to say if it was because I was tired and not paying close enough attention, or simply because there was not much to see, but the first dive at “Cabo Pierce” was fairly uneventful and my photography endeavors resulted in little other than a few pictures of fish and an Octopus. As with many dive sites at the Revillagigedo Archipelago, this “Cabo Pierce” is a lava flow that takes the form of walls. The dive site itself starts at about 80 feet, making it a fairly deep dive if your intention is to avoid decompression obligations. My maximum depth on this dive ended up being 100 feet, but I stayed down for 45 minuets and racked up a little bit of deco… I was breathing air after all.

After getting back to the boat, drinking a little coffee and eating breakfast I went to work straight away on putting my rebreather together and pre-diving it. Diving Rebreathers is a form of technical diving and it requires a lot more work and attention to detail than open circuit diving. Because of this, rebreather divers are frequently the target of taunting and snide comments by open circuit divers. You almost get to the point where you stop hearing it when people say “my, those things certainly are a lot of work”, or “seeing how much work those things are to dive, I think I’ll stick with my traditional SCUBA gear”. Perhaps they’re just jealous. Technical diving is not for everyone and since most people don’t want to do long, deep dives, they’re probably better off with standard equipment and techniques anyhow. All told, I spent about an hour getting my rig ready to dive and finished just in time to make the second dive of the day. Not wanting to fight with the strong currents we encountered on the first dive, I decided to do this one by myself and explore the lava formations inside the large cove near the island itself. I jumped right off the back of the Nautilus, descended to the sandy bottom at 100 feet and started swimming towards the island, keeping the sun at my left for reference.

As I neared the island, I found myself in about 50 feet of water, both hearing and feeling the songs of Humpback Whales. We’d heard Humpbacks on many of our other dives, but in the case, the sounds were amazingly loud and I could actually feel the low frequency waves travel through my body and head. I can only imagine that the creature itself must have been very close, but despite constantly looking, I was unable to see it. The sounds diminished as I neared the island, and I found that the shore was not so much the sheer wall I had imagined, as it was a series of walls that were formed by lava flows. I didn’t see much in the way of animals, but thoroughly enjoyed exploring the flows and lava formations. At one point I even found a small cave which started in about 40 feet of water and ended roughly 40 feet back and 30 feet deep. All told, I stayed down for 1 hour and reached a maximum depth of 100 feet.

For the third and last dive of the day we went to a site called “La Pitite Boiler”. This site is a small stone pillar that begins on the sea floor at 130 feet, and extends up to about 5 feet below the surface. It is named for the way the water seems to boil as the waves pass over it, briefly exposing the peak and then submerging it again. We descended directly to the bottom at 130 feet and basically swam laps around the towering stone getting shallower and shallower on each pass. The surface was fairly rough, but there was little to no current and the dive was extremely fun. We saw quite a few Moray eels, although the larger animals eluded us. It’s hard to say exactly how many laps I swam around the pillar, but I stayed in the water for an hour and enjoyed every second of it. When I did decide to surface, I did so mostly because I didn’t want to keep the other divers waiting and because it was getting dark. I could have happily stayed down for another hour!

We pulled anchor and started heading back to the island of San Benidicto for our last day of diving before dinner. The seas were rough, which made for some interesting displays of plate and cup handling skills during our meal. I had a couple of Gin and Tonics and headed off to bed. Since we were going back to “The Canyon” I had designs on doing some deeper dives in the morning.

John, however had mentioned the night before that we WOULD see more creatures today, and that there was simply no way around it. We joked with him that he had sent out a telepathic signal to them, and that they were surely swimming toward us now, but unlikely to arrive before our departure. We all had a chuckle at the idea of hundreds of confused Pelagics swimming around island several days later, wondering where John had gotten off to. Telepathy or not, whatever he did worked because the number of large animals we saw on day two at Roca Partida made the first day seem like diving in a sterile lake.

Because I was still diving open circuit, and had little to devote my attention to other than just diving, I decided to try my hand again at photography. Unlike the day before, but camera worked perfectly and most of my underwater shots from the trip are from this day. I even took a video of one of the Mantas that came in close and interacted with us.

The first dive of the day was wonderful. I still found myself looking down into the depths, wanting to dive to the peak of the submerged volcano at 250 feet, but the fact that we saw a large black Manta and a group of Hammerhead sharks right way made staying in shallow water a great deal easier. I actually only went to a maximum depth of 85 feet on this dive, but there was so much to keep my interest that I stayed in the water for nearly an hour.

The second dive was much the same, although I descended to 95 feet this time in hopes of finding some more Hmmerheads. I found a great number of Silky Sharks, but the Hammerheads eluded me. I ascended to around 50 feet where I had another wonderful interaction with a black Manta and found a lot of large Tuna. I finished out my 1 hour dive in the 40 to 50 foot range and enjoyed taking in the scenery.

There really is something about doing dives that don’t have a visible bottom that makes you feel like you can fly. Many of the divers described the Mantas as Sirens that call you out into the blue away from the visible topography, and I can attest that they most certainly do. I think of myself as a very disciplined diver who maintains awareness of his surroundings and topography at all times, but when a large Chevron Manta showed up on our third and final dive at Roca Partida, I was amased at how, after only what seemed like a kick or two towards him, I was much further from the island than I expected to be. This is not to say that I could not see the topography, but it made it very clear how one might get into trouble swimming with Mantas. As I was still fairly close to the island, I decided to simply hover at 85 feet in the water column and let the giant Manta make several passes at me. As an added bonus we had some large Silvertip Reef Sharks make passes by us as well. All told, I stayed in the water for an hour, and reached a maximum depth of 90 feet. It was a wonderful way to say goodbye to this amazing dive site.

That night we pulled anchor and headed back to Socorro for another day of diving. I was tired, so I slept well despite the constant rumble of the boat’s engines.

Because of the remote and exposed location of this dive site it is important to have good weather or the swell becomes too large, and the site undivable. So, when the weather report came back fovorable for the next few days the decision was made to pull anchor and begin the 60 mile trip to Roca Partida, where we would spend the next few days diving. Because these islands have not been re-charted since the advent of GPS, the moving map displays on the ship are not always totally accurate and the crew prefers not to maneuver the boat around the tiny island at night if it can be avoided. I, myself, got somewhat confused at one point when I turned on my little Garmin GPS and found that it had me placed right on the beach of Socorro when I was quite clearly standing on the deck on the Nautilus Explorer! Anyhow, the trip would take about 12 hours, so we decided to leave Socorro for Roca Partida after dinner so that the sun would be up by the time we arrived.

To my surprise, the dive briefing that night included very little of Sten’s humor and joking, but instead a lot of stern warning about not loosing visual reference to the topography and the importance of surfacing near the island. Because it is basically an open-ocean dive site and there is no shotline, a diver that surfaces very far from the Zodiac or skiff is difficult to see, and can easily become lost at sea. While we all carried surface marker buoys (SMB’s) and mirrors to mitigate the risk, the warning was clear. “Never lose the topography underwater. If you become disoriented, surface without a safety stop and inflate your SMB.” Sten saved the most chilling warning for last, reminding us that if we became lost the only Boat looking for us would be the one we were on, and that if we were not found by dark we would not be found.

That night I did not sleep well, and woke up entirely too late to get my rebreather configured to make the first dive. Instead, I lounged around, drank coffee, and leisurely pre-dove my rig. Rich, on the other hand made the first dive and mentioned that maintaining counterlung volume was difficult above 30 feet because of the substantial swell. We both made the decision to dive open circuit at this site and I carefully packed up my Meg beneath my bunk.

My first dive of the day was great fun, but something in my brain forgot what it was to dive standard SCUBA gear, and I emptied my tank to 500 PSI after only 45 minuets in the water. You can breathe as hard as you like on rebreathers, but not so on open circuit. I had borrowed my gear from the boat, and was surprised to look down and see that my borrowed dive computer, a TUSA IMPREX, read that I was at 155 feet! My trusty VR3, a dive computer that I have depended on for years, and one that has been used on many a gnarly tech dive read only 100 feet, so that was the one I decided to trust. The IMPREX racked up quite a deco obligation, so I went ahead an cleared it while playing around in 30 feet of water or so. The 30 foot level turned out to be the most interesting anyhow because we saw a large Manta, some White Tip Reef Sharks and some large Tuna towards the end of the dive. It was difficult to maintain a constant depth, however, because of the strong surge and swell.

The second dive of the day was much the same as the first, except my camera ran out of batteries about half way through the dive and I did not consume nearly as much gas. By this time I had ditched borrowed regulator in favor of another borrowed regulator, and no longer had to suffer the greatly exaggerated depth displayed by the IMPREX. I swam a total of two laps around the island at a maximum depth of 100 feet, but saw little other than a few sharks and large groups of bait fish. The entire dive lasted about 45 minuets.

By the third and final dive of the day, it was getting dark, and again, we saw only sharks. My camera was working perfectly, but I had too little light for much other than macro shots on the rock. I did get some interesting pictures of little shark dens where juvenile White Tips would gather to rest, sometimes among Moray Eels. Again, I circled the island two times at a maximum depth of 120 feet, and the dive lasted 45 minuets.

Roca Partida did seem to be a great dive site, but at the end of the first day my feeling was that it had been hyped quite a lot. We had only seen Mantas on the first dive, and I was a little unhappy that I didn’t have any helium with which to dive down to the are where the pillar leveled off at 250 feet. The conditions were rough, but not nearly so difficult as had been let on, and a part of me wished we were not spending two days there. I had no way of knowing at the time, but the next day would do a lot to change my mind!

Actually, while on the topic of Dive-master Sten, I should say that I have never in my life experienced such detailed and thorough dive briefings. A tall and very quick-witted Sweed, Sten’s briefings were hilarious and entertaining on top of being incredibly informative!

Our first dive involved tediously pulling ourselves down the shotline against a very strong and troublesome current. Normally this would make for a difficult and disappointing dive, but in this case an incredibly friendly dolphin decided to join us as we pulled ourselves against the current. Mockingly demonstrating how easy it was for him to swim against the strong current, the dolphin situated himself next to us on the line, blowing the occasional bubble from his blow-hole, and practically begging us to touch him.

Now, of course, finding such a friendly and interactive dolphin is somewhat of a dream come true for many divers, and as the dolphin flirted with us, the already crowded and chaotic shotline became a sort of underwater trainwreck with divers packed tightly against each other. Being the big baby that I am, I admit to having some concern that my rebreather would get scratched or dinged, but it escaped unscathed, and I was forever grateful to have had such a wonderful encounter with this amazing creature.

The dolphin followed us to the bottom where the lava flows provided some protection from the strong current, but the surge was still quite strong. Rich and I followed the wall out to a maximum depth of 100 feet, where we found the surge to have let up quite a lot. We did not stick with the larger group, but they reported that they saw a group of Hammerhead Sharks. The entire dive lasted 45 minuets.

The second dive of the day did not feature such a flourish of wildlife as the first, but at a maximum depth of 140 feet it was my deepest dive yet on the Meg. I decided to do this dive alone, and descended to the bottom of the wall with the hopes of finding some sharks. in the end, however, I only managed to find a large yellow Tuna, and a lobster. I enjoyed the dive greatly though, and spent an entire hour exploring lava flows and looking into the blue beyond the wall.

The third dive of the day was much the same as the second, although we saw some large Silky Sharks. I did not descend to the bottom of the wall this time, choosing instead to swim about 20 feet above the sandy bottom at a maximum depth of 120 feet. I exited the water after 45 minuets, and decided to change out my scrubber material and skip the last dive of the say. That night we pulled anchor and headed off to Roca Partida, the smallest of the Revillagigedo Archipelago.

My first dive at The Canyon was enjoyable, but never having used my rebreather with anything other than a drysuit, I was unsure how much weight I would need with my new 5mm wetsuit, and the 12 pounds I added made me grossly over weighted. I also experienced trouble sealing the membrane between my nose and throat, so I was constantly, albeit slightly, breathing in and out through my nose. This effectively resulted in me drinking whatever saltwater came into my mask, giving me a burning sensation in my sinuses and a queasy feeling in my stomach.

Not much worse for the wear, however, I stayed down for 35 minutes and descended to a maximum depth of 90 feet, but did not get to see the group of Hammerhead Sharks that my buddy Rich saw. All in all, it was a great shakeout dive, and seeing the Manta was a real treat. It was clear, however, that I would need to remove quite a lot of weight from my rig.

The second dive was much better, although we did not see any Mantas. My nasal membrane sealed up much better, though not perfectly, and the 6 pounds of weight I had removed resulted in much better trim. I descended the wall to a maximum depth of 120 feet, where we encountered a fairly large group of White Tip Reef Sharks. We stayed there for a while to watch them, but decided to head back after we had incurred about five minuets of decompression obligation. On the way back to the shot line, we saw a large Stingray, and a couple of Moray Eels. The entire dive lasted 45 minuets.

The third and final dive of the day was much the same as the second. By this time I had removed all the weight from my rig, and found that it was trimming out perfectly. We descended to a maximum depth of 100 feet, and encountered a group Silver Tip Reef Sharks. I had been struggling all day with finding a way to use my new Jet fins, but even diving with sneakers on, I found that my right, big toe was killing me on this dive. The problem was that fins were sized for my DUI rock boots, and both the wetsuit boots and sneakers moved around too much inside them. After this dive, I decided I would switch to my Scubapro Twin Jet fins. I only stayed down for 35 minuets on this dive because I was getting tired and my toe was hurting so much. It was a great dive though, and I was looking forward to getting some sleep and diving the next day.

Because of the extremely remote location, only a select few dive boats are even capable of running trips to the Revillagigedo Archipelago, and of these, only two have been granted the licensees required to do so; the Nautilus Explorer and the Solmar 5. Our trip was on the Nautilus Explorer.

While we spent a total of nine nights and seven days aboard the Nautilus, it takes about 24 hours to reach the Northern most island of San Benedicto, meaning that two full days and nights must be spent at sea. This left us with five days of intense diving, usually making four dives per day, and sometimes even snorkeling with the sharks at night. Needless to say everyone slept very well at night!

The diving at these islands is really quite nice. The water temperature was running about 70 degrees F, which matched up perfectly with the 5mm wet-suit I brought with me. While the deepest dive I made was only 160 feet, I chose to dive my Megalodon rebbreather on all the dives except those on Roca Partida, which had so much surge and swell that maintaining counterlung volume became very difficult in water shallower than 30 feet.

The biggest draw to the Revillagigedo Archipelago is, of course the giant Manta rays, but for me the sharks were perhaps the most interesting. We saw countless White and Silver tip Reef Sharks, and Hammerheads were also quite common. The divemasters commented frequently that the Mantas were much more friendly in on prior trips, but a few did allow us to interact with them. For me, the most memorable experience of the trip was a very friendly Bottlenose Dolphin that swam up to me and practically begged me to pet it.

Again, because of the remoteness of the location, as well as the cost of helium in Mexico we did not make this a technical diving expedition. While there were a number of times I desperately wanted to descend below 200 feet, this trip served as a great opportunity for me to really put some hours on my rebreather, and get myself geared up for some more aggressive diving in the coming season. I find that every dive I am trusting the CCR technology more and more, and diving the unit is starting to become second nature.

Stay tuned. In the coming days I will write about each of the dive sites we visited, and the animals we saw there.

Revillagigedo Archipelago Facts

Indeed, a number of enterprising divers have totally re-invented the housing and harness system. Janwillem Bech’s Travelframe is a good example of this type of innovation. It allows the entire rebreather to fit into a carry on bag, and adapts it to a Hogarthian backplate and harness system, making the use of side-mounts much much easier.

The latest in the series of these custom-made Inspiration / Evolution frame systems is called the Titanbox, and it is truly a work of art! Designer Michael Hearn at Dive Designs must be a master craftsman because the his frame is not only very well built, but absolutely beautiful as well. Hearn writes:

When I started diving the Inspiration rebreather a few years ago, I noticed the original case of the inspiration is limited when it comes to use bigger cylinders or attaching extra accessories such as battery’s.

As I was searching the web and dive shows for a scrubber assembly case, I never found what I was looking for.

So I decided to design and built my own case in one of the most indestructible, non corrosive and affordable metals of all: titanium. As titanium is very expensive and difficult to work with, I also built a hard anodized aluminium version.

He is offering them for sale, but as one might expect in the world of rebreathers, they don’t come cheap. The titanium model can be had for just under $2,000, while the allumnium version comes in at a little under $800.00. As far as I can tell it’s worth every penny though if you have an inspiration. I know I’d have my order in if I’d gotten one instead of my Meg.

Well done!

More info and tons of pictures can be found at Michael’s website.

Hat Tip: TheRebreatherSite.nl

When building these systems, many people decide to incorporate quick disconnects at the supply side to facilitate quick changes in gas for making custom blends. This allows for the adaptor to stay connected to the industrial gas cylinder, while making it easy to move the whip from gas to gas. This is a great design in theory, but these connectors tend to develop leaks over time, which can be frustrating and costly, especially when working with helium.

In order to maintain the flexibility of quick disconnects without the problem of leaky connections, Keith had the brilliant idea to standardize the entire system on SCUBA DIN connectors. This makes switching source gas nearly as easy, but results in a much more solid and leak-proof connection. A male DIN connector is at each end of the fill whip, and all bulk cylinder adaptors have a female DIN connector on the whip side. Connecting up your source gas becomes as easy as screwing in your SCUBA first stage.

In the interest of being thorough, I decided to get the system with just about every type of cylinder adaptor imaginable. For the time being, I really only plan on doing transfils from industrial gas cylinders for my gas blending, but at some point I may decide to hook it up to a booster. My rebreather tanks are only 20 cf, so I can’t really justify the cost at the moment, but if I ever start making TRIMIX in anything larger, I will have to invest in some type of booster to make the helium go further.

Innerspace Systems is poised to release their own version of the Cis-Lunar scrubber, but as of now, they are not selling it to the general public, and there is really no word on when they will. If you want a radial scrubber in your Meg your only options are to wait for someone to sell their Cis-Lunar scrubber and be prepared to take out a second mortgage on your house to buy it, or build your own.

As it happens, building one is exactly what Ken (skipbreather) over at rebreatherworld did. Not only did he build one for himself, he also published all of his shop drawings so that, with a few tools, we can all build our own. He estimates that the materials cost about $300, but unless you have a pretty well-stocked shop, you are likely to need some new tools as well… Darn. Don’t we all just hate to buy new tools.

Anyhow, check it out. Depending on how much the ISC version costs, this may be the direction I go.

The cool thing about rebreathers is that you can talk into them, and people can understand you. Sure, if sounds like you have a mouth full of rubber (which you do), but you can still be understood. I’m guessing that these guys found a pretty serious thermocline, and the water got a great deal colder than they anticipated.

Pyle is clearly disturbed by this unfortunate turn of events, and spends quite a lot of time swearing and complaining about the cold water. I guess we can’t really blame him for not piling on the thermal protection though. He was, after all off Christmas Island in the Central Pacific Ocean. It’s only five degrease north of the equator, so the water should, in theory, be pretty warm.

]]> http://spiralbound.net/2006/06/02/dont-swear-into-helium/feed 0 http://spiralbound.net/2006/04/05/rebreather-evaluation-part-5-my-decision http://spiralbound.net/2006/04/05/rebreather-evaluation-part-5-my-decision#comments Wed, 05 Apr 2006 15:06:32 +0000 cliff http://spiralbound.net/2006/04/05/rebreather-evaluation-part-5-my-decision/ 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.

Rebreather Evaluation – Part 4: The Megalodon >

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.

Rebreather Evaluation – Part 3: The PRISM Topaz >
Rebreather Evaluation – Part 5: My Decision >

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.

Rebreather Evaluation – Part 2: The Inspiration >
Rebreather Evaluation – Part 4: The Megalodon >

The wreck sank in 1981, but slid into deeper waters because of a storm in 1985. It currently sits in water ranging from 145m to 160m, and perhaps even deeper. The two divers ventured to 160m on TRIMIX, which is admittedly a very deep dive.

The team plans to return to the Yolanda in August to dive even deeper in search of other parts of the ship. Cunningham works as a TDI Instructor Trainer, and Andrews is Technical Director at the London School of Diving.

More information can be found here.

Well done guys!

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. Thanks to Elite Divers for the breakdown.

• 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.

Rebreather Evaluation – Part 1 >
Rebreather Evaluation – Part 3: The PRISM Topaz >

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, and am publishing my product evaluation in a five-part featured series. 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 links below will become active as each part to the series is published.

Rebreather Evaluation – Part 2: The Inspiration >
Rebreather Evaluation – Part 3: The PRISM Topaz >
Rebreather Evaluation – Part 4: The Megalodon >
Rebreather Evaluation – Part 5: My Decision >