My experiences in rebreather diving

[Dive-aholic]

Okay, I’ve had my KISS GEM PSCR for a few weeks now and have done a few dives on it since training. I’ve had some requests to start a thread about my experiences with the GEM, so here it is.

Let’s start with why I chose the GEM. I’ve gotten to a point in my diving where my dive time is limited by the amount of gas I can carry. While my RMV is fairly low (.35-.45 range), I’ve found myself having to bring along a couple of stage cylinders in addition to my sidemount cylinders. Adding a 3rd stage cylinder isn’t really practical, so a rebreather seemed the appropriate solution.

In discussing this with some people, the first response I usually get is, “you still need to bring enough bailout to get out of the cave.” I’m well aware of this, and what those people don’t understand is that not all cave penetrations are necessarily linear. In other words, just because I’m doing a 3-4 hour long dive in a cave doesn’t mean I’m 1.5-2 hours from the entrance. Caves are mazes and one can spend a lot of time in the 3000-4000’ penetration area. I have swam out of Jackson Blue, average depth 85-90’, from 2500’ penetration on an AL80 while pushing a scooter in front of me during low flow and still had plenty of volume left in the cylinder. I’m diving my GEM on a set of cave-filled LP 85s, one of which is about 1.5 times the volume of an AL80. One LP 85 alone is enough bailout. Add the 2nd one that’s plumbed into the GEM and that’s more than enough gas to get out from 4000’ back in a 90’ deep cave a couple of times.

As many of you know, I typically dive sidemount, and not just for the configuration, but also for the passages I dive. One of the key considerations in choosing a rebreather has always been the ability to sidemount it. My reason for wanting a rebreather, as stated above, was gas extension. While I do deep dives on occasion, I much prefer to spend more time diving and less time decompressing. While CCRs can be somewhat advantageous on deep dives, I’m fine doing those dives on OC. I needed something that would simply allow me to stay in the 80-100’ depth range longer without carrying half a dozen cylinders. When I saw the KISS GEM at DEMA last year, I had found the solution to my problem. The GEM is compact and can easily be mounted in a low profile position with a sidemount configuration. I hadn’t really considered an SCR before, but the GEM had my attention.

As I said, the GEM can easily be mounted in a low profile position. I have rigged it up so I carry it in a similar manner as I do a stage cylinder – on top nestled in between my right sidemount cylinder and my torso. The GEM is a gas extender. The current mouthpiece is a 3:1, which means it can extend gas 3 times what it is. In other words, the 116 cf in my LP 85 becomes the equivalent of 348 cf on the GEM. I’ve heard rumor of 5:1 and 8:1 mouthpieces being produced in the future and was considering getting one, but I don’t think that will be necessary. I was able to get an RMV of .128 on my last GEM dive. I’ve had as low as .07. Planning on an average RMV of .12, I can get 4 hours from an LP 85, 4.5 from an LP 95. At this point the scrubber becomes my limiting factor, not the mouthpiece.

I’ve done rebreather tryouts before, including over an hour diving a KISS Classic CCR, and 15-20 minutes each on a Meg and a Dive Rite Optima. I know most people have issues with buoyancy control when they go from OC to diving a RB. That wasn’t an issue for me. I knew what to expect and didn’t fall into that with the GEM. I had already experienced it on my KISS Classic dive a couple of times and it was enough to get it ingrained in my mind. The most difficult part of diving the GEM was the work of breathing. Finding the perfect position for the counter lungs has been the challenge. I played around with the position and finally found where I get the least work of breathing. One thing about the GEM is the counter lung covers are small. KISS uses 4 liter MSR bags, but the covers don’t allow for full expansion of the bags. My first couple of times on the GEM resulted in pretty significant gas consumption because I had to exhale a little through my nose on every breath, thus causing the GEM to have to pull in more gas during every exhalation. This issue was easily resolved by removing the MSR bags from the covers.

With the MSR bags removed, I moved them around until I found the best place for breathing. I’ve also found that I have to retrain myself on breathing underwater. On OC, I typically only take 6-8 slow breaths per minute. Before anyone says it, I don’t skip breathe. I’m not holding my breath, just breathing slowly. That’s not the way to do it on the GEM. Breathing has to be more like it is on the surface. I was finally able to retrain myself somewhat, but until I have more time on the GEM, it will take some concentration to breathe properly on it, especially since I’m still spending more time on OC than I am on the GEM. I may end up putting the MSR bags back in the covers, but definitely without the bungee that are used to retract them.

Another thing I discovered is I tend to fin much like I breathe. On OC, I fin very little, but am still able to swim at a pace of about 50 fpm. During my last GEM dive I noticed I was finning along with my breathing. So my glide was gone! I really had to concentrate to slow my finning down. That will be something else I need to work on. I guess it really doesn’t matter for my RMV, but it would be nice to not fin so much. It was making me tired!

I did notice that if I distracted myself I was more likely to fall into my usual slow finning pace and breathe easier. I decided during my last dive to do a little survey work and was able to just fall into the task of collecting data while monitoring my ppO2 regularly. I also noticed my breathing and finning relaxed somewhat. I think more time on the unit will lead to that happening without the distraction.

One of the things I don’t particularly like about the GEM is the length of the loop hoses. While I understand the GEM is being marketed to recreational divers and the long hoses may work for them, the length doesn’t work for the diving I’m doing. I’m still working through how I will deal with the hose issue. It’s not a pressing issue since I don’t plan on taking the GEM into small passage without more time on it.

The nice thing about the GEM is that once I get everything dialed in and more time in it, it won’t be an issue to dive in mixed teams. As I said earlier, I have the GEM plumbed into my right sidemount cylinder. I still have a 7’ hose on that cylinder and my left cylinder is no different than it is in sidemount. Rather than pulling the 7’ hose all the way out and routing it around my neck, I leave it tucked into the retainers on the cylinder and clipped off to my waist d-ring. If I need to donate it, I simply grab it and pull it, breaking the zip tie and pulling it loose from the hose retainers. I still have my left cylinder for bailout.

I also have my GEM plumbed so I can swap cylinders with a quick release. Some people have suggested I use a gas switch block, but I’m not sure I really need that. It’s simple enough to disconnect from one cylinder and connect to another. That also means I can plumb my decompression cylinder into the GEM at the end of the dive and continue to breathe warm, moist air, even during that portion of the dive. And with longer bottom times, the decompression will also become longer, so keeping the gas warm and moist will be nice.

Overall, I’m happy with my decision to buy a KISS GEM. Once I have a little more time in it, I’ll be taking it on some of my usual dives and putting it to the use I intended it for when I bought it. The true test will be riding my Magnus without having the mouthpiece fly out of my mouth because of the force on the loop!

 

[TSandM]

Thank you for a thoughtful review of the device. I think even GUE would approve of your reasons for adopting it

Out of curiosity, and perhaps because I missed it, did you take any training on the unit? Education in procedures for flooded loop, etc?

 

[Dive-aholic]

Yes, I did train on the unit. Had to since my instructor had the mouthpiece! Training was done with the unit in it's out of the box form and isn't any different than training for any other SCR. The real experience started after the training.

 

[Jax]

Great write up! However . . .

:worthless:

 

[w ripley]

Nice post. I think most of us spend a lot of time (and money) getting our rigs right for the type of diving we're doing and for how we dive.

FWIW, my rig has a vibrating HUD, which has caught me more than once not breathing as regularly as I should, ie, not pushing the air around the loop like I should. After a while the new breathing pace will feel natural.

I hope that you will repost after you reach your first and second 100 hours on your unit. It would be nice to see how you've further modified yours and what, if anything, you are doing differently then.

Thanks for your post.

 

[Jax]

FWIW, my rig has a vibrating HUD, which has caught me more than once not breathing as regularly as I should, ie, not pushing the air around the loop like I should. After a while the new breathing pace will feel natural.

I haven't a clue what that first part means, but have a curiosity question: Do you change breathing pace as you swap from OC to ?CR, or do you adopt something that works for both?

 

[w ripley]

I haven't a clue what that first part means, but have a curiosity question: Do you change breathing pace as you swap from OC to ?CR, or do you adopt something that works for both?

To answer your question first, you normally don't switch between OC and CCR on a dive, unless you have trouble with your RB and have to bail out to OC. If you have a bail-out valve (BOV) on your mouthpiece, which has a second-stage reg as a working part of it, you may test it every so often before and during a dive, but not for any extended period of time. If you bail out to a separate bail-out bottle, then it will have a second-stage reg attached to it. If you have to leave the CCR for any reason, then you would be on OC.

When on OC and taking it easy, say swimming slowly where there is no current or resting on the deco line, then it's easy to breathe slowly. With a RB there is another issue.

First, a HUD is a Heads-Up Display that sits out in front of your mask to tell you what your RB's oxygen sensors are reading. As you probably know, there is a closed breathing loop with a RB and you need some way of knowing what the percentage of oxygen is in the air you are breathing. When you are breathing air that is fine your HUD will generally flash green. If the air is hypoxic or hyperoxic then your HUD will flash red. There's more to it, but that's the general concept. FYI, the oxygen sensors also send the data to your handsets that let you read precisely what that percentage of oxygen is.

My RB has a HUD which not only shows the red and green but also vibrates when the sensors read air that is hypoxic or hyperoxic.

When you exhale into the RB's breathing loop, your breath is generally hypoxic. If you don't move that hypoxic air fast enough within the loop, so that it will mix with the other air in the loop, you can actually push that hypoxic air past the oxygen sensors. Naturally the sensors will read the hypoxic air and send an alarm to the HUD. In my case it will also cause the HUD to vibrate. If I check and find that everything is OK, but that I'm just not breathing fast enough (actually, not breathing steadily enough) then I adjust my breathing accordingly.

It doesn't take too long to figure out what the RB wants to see. You have to recognize that on a RB you are the "motor" that makes the breathing loop work. It's not hard, just something you have to do.

I hope that makes some sense and helps.

 

[Jax]

Wow . . . thanks, that makes it a lot clearer.

I understand one doesn't switch between OC & RB on a dive, but how does that different pace of breathing affect you if you go on an OC dive? As Rob stated, he has learned to breath slowly and deeply on OC, but must change the pace on RB. Now, if he goes off the OC and back onto sidemount . . . or if YOU go diving OC . . . do you keep the pace of breathing of the RB? Do you re-acquire your OC breathing pace? It seems like it might not be so easy to change something so ingrained when one swaps rigs.

 

[Dive-aholic]

I do have plans for such a scenario. I've "bailed out" on occasion just to practice it since I'm new to this. So far my breathing adjusts to whether I'm breathing OC or SCR. But I am new to the whole RB thing and still diving OC a lot more than I'm diving RB. That might change in the next few months.

Bill, I will definitely keep updating this thread as I progress through my experience. I do have plans for mods, but I'm hesitant to post anything regarding those plans at this point. It's a new unit that's still under warranty, and being new to it, I don't want anyone to follow suit since I don't have a whole lot of experience in this. Granted, I'm talking to people I know and trust that have tons of RB experience and getting advice on the mods I want to make, but I still don't feel like it would be prudent to discuss it right now. But in 100 hours I may feel different!

 

[w ripley]

Wow . . . thanks, that makes it a lot clearer.

I understand one doesn't switch between OC & RB on a dive, but how does that different pace of breathing affect you if you go on an OC dive? As Rob stated, he has learned to breath slowly and deeply on OC, but must change the pace on RB. Now, if he goes off the OC and back onto sidemount . . . or if YOU go diving OC . . . do you keep the pace of breathing of the RB? Do you re-acquire your OC breathing pace? It seems like it might not be so easy to change something so ingrained when one swaps rigs.

Good question, and you've got a good hold on the answer.

The simple answer is they aren't that much different. You breathe as required on OC and breathe at a steady, but relaxed, rate on CC. That's why there is so much attention paid to "Work of Breathing" for rebreathers, as each has a different one. The easier they breathe the less effort it takes to move the air around the loop, and the less you notice any difference between OC and CC.

Actually you can hold your breath on a RB as long as you like. It's just that when you exhale you have to do so with conviction, for the reason mentioned in my earilier post - mixing the air and pushing it around the loop.

The long answer is that when on OC, especially on long dives, you are trying not to "waste" the air you've carried down with you. You learn to breathe according to the work requirements. It's like being in a car at night on a long trip on the interstate with the fuel gauge getting close to empty: You just don't gun the engine and you try to keep your foot off the gas pedal as much as you can, so as to "stretch out" the gas you have. Same thing for diving OC, at least for me.

The RB changes all of that. Because you are recycling your unspent oxygen, you are no longer looking at how much gas you have but how much deco time you are accumulating. With my rig, if I stay down 6 hours I usually haven't used half of my available "onboard" gas when I surface (onboard gas is the air I actually have attached to my rig, and doesn't count the bailout bottles I am carrying + those I have planted along my path in a cave or have hanging on the hang line). So, it's a completely different mindset. You aren't keeping your foot off the pedal, so to speak, so you don't feel the pressure to slow down.


Easy breathing on OC also helps with you buoyancy, as you rise in the water column when you inhale and fall when you exhale. The more gradual you inhale and exhale the smoother your trim is. With a RB, there is a counter lung which expands when you exhale (as your lungs get smaller) and gets smaller as you inhale (as your lungs expands). So, it doesn't matter how much you breathe or at what rate, as far as buoyancy is concerned, because breathing on the loop on a RB doesn't really affect your position in the water column.

One last point and that is when you go to OC from a RB it's because you're having a problem. Don't know about you but when I have a problem underwater my heart rate increases as does my breathing. So, when I bail out to OC, I'm usually not breathing at a relaxed rate but taking some pretty big swiggs of air, at least until I calm down a little. In those conditions, at least for me, it's not about noticing a breathing difference but more about getting air in my lungs.

Again, hope this helps.