Scuba Force's Sf2 Rebreather... With Training By Tom Mccarthy

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that is a heavily debated subject and depends largely on the scrubber design, but either way with being able to comfortably maintain a 6l tidal volume for things like kicking into high flow caves, I'd rather not be exhaling against the opv and inhaling against an adv on every breath, especially with the counterlung that far down.
A lot of co2 issues happen during times of exertion, not sure who debates that? Deleting co2 laden gas reduces the overall burden on the scrubber. Again who debates that?

Exhaling against the OPV might be an issue if its set improperly (mine is pinned) and inhaling against an AVD might be a problem in some RB designs, but bellows counterlung units operate like a normal 2nd stage except with a big huge diaphragm. In my experience its not very different in feel than a typical 2nd stage.

Also, if you're close to flat, the breathing resistance is pretty much nonexistent.
 
the debate seems to be over whether or not you can actually outbreathe the scrubbers and using a rebreather like a CCR or bailing out is of any meaningful benefit vs. staying on the loop. Either way, I have a try dive coming up on the SF2 and that is the only way to verify all of this.
 
Staying on the loop when you're having a co2 issue isn't a smart move.

And you can certainly over breathe a scrubber.
 
Staying on the loop when you're having a co2 issue isn't a smart move.
I would agree with this!!! Hypercapnia means an immediate bailout.

Well, I finished the class. @Tmccar1 beat my butt 4 days in a row. He was brutal, and I'm glad he was. I have never had such a thorough class and to think it was only a crossover. Great job, Tom, and THANKS!

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Don't worry, there's a lot more for me to write. I was too whipped while I was taking the class and I've got an private OW student in the morning. Keep tuned in here and I'll clue everyone in on what I went through.
 
I'd rather not be exhaling against the opv and inhaling against an adv on every breath, especially with the counterlung that far down.

The ADV on the SF2 is super smooth. It actually makes it hard to keep at min loop volume on SM because you almost can't tell you have bottomed out the CL and are adding gas. After several dives I managed to get attuned to it, but it was by far the trickiest part of learning the SM unit. From looking at pictures on the net, it looks like a lot of people don't ever figure it out, so they end up strapping on a 3lb weight to keep it from getting buoyant.

Before I crossed over I was a little worried about the low CL volume, and the fact that there was only one of them. Turned out to not be a problem at all. As a benchmark, last time I had my lung tidal volume measured, it was a little over 7L.

-Chris
 
The weekend is over, I've finished my OW student and I'm able to put my thoughts down here on SB about my Scuba Force SF2 class with Tom McCarthy.

Day 1: Getting to know you!
The first day was fun, relaxing and yet a bit troubling. I drove up from Key Largo to Tom's parent's house in Pompano. Getting out of the door was a bit chaotic, and I had to double back for my laptop. The directions were clear, the traffic was tolerable and I was stoked when I got there. @Tmccar1 had already clued me in that this was going to be a gear and class day, so I was mentally prepared for it, or so I had thought. After all, I had read the English translation of their German manual twice and I had read both their translation of the Petrel 2 manual as well as the DiveCAN manual I found on Shearwater's site. As previously noted, I had already assembled my SF2 and was eager to get Tom's input.

The first order of business was for Tom to pull my rebreather apart and test everything. Everything. He carefully explained things as he went along, being sure to clue me in on the workings of the four isolators. Somehow, I had gotten everything assembled correctly, including the dil and oxy tanks on the correct sides. He even liked the M8 x 1.25 knurled knob I had gotten to replace the boring wing nut that comes with the unit. Instead of bringing the teacher an apple, I brought him one for his SF2 :D :D :D

61Bi-qfJBdL._SL1181_.jpg

I'm a gear head, first and last, so it was no problem for me to pay close attention to everything uttered by Tom. It's obvious that he really understands this unit and every feature completely. So then, we proceeded to scrubber packing, unit assembly and testing. Tom not only teaches you how to do this, but why you should do it in a particular manner. I believe in having printed checklists for rebreathers and the manual didn't have one. Fortunately, Tom had a great one prepared for me. I had already started developing one in my head, but this one was far better and followed in a logically progressive manner. I won't have to reinvent the wheel here!

After an excellent lunch, Tom really blew my mind.

During the afternoon, Tom did his level best to baffle me with various scenarios and dry drills. I had been trained on a rEvo and a GEM, neither of which were an eCCR. Consequently, I really had to expand my mind to encompass the additional failure possibilities I could encounter as well as to meet Toms high expectations. He hit me with hypercapnia, hyperoxia, hypoxia and boom drills. As soon as I thought I had it, Tom added another wrinkle. I thought I understood what the isolators were for, but by the end of the afternoon, I KNEW what they were for. It was the most intense session I've ever had. It would be eclipsed over the next few days, but up to that point it held the superlative.

Don't misunderstand... this was not a hazing. When I didn't understand something, Tom methodically and patiently explained it in a way that most anyone could understand or he lead me through a discovery. That didn't stop him from being relentless and keeping me on my toes. I really liked the discovery method and am glad that it was continued through the class. It's one thing to be fed an answer. It's far better to figure some of it out on your own. To be frank, there were some parts that I should have known, being a CCR diver. I just don't think it was covered in my previous class. In fact, I'm pretty sure of it. That was the troubling part of the day. Importantly, I know it now and I have Tom to thank for that. Troubles be gone!

That evening I was treated to an awesome dinner and then Tom and I did the classwork and Power Points in the living room. We checked the weather, and the seas didn't seem appealing in Pompano or the Keys. It was decided that we would scoot up to Blue Grotto in the morning to continue the diving portion of this crossover. I was exhausted and slept well. It was a great day.
 
The weekend is over, I've finished my OW student and I'm able to put my thoughts down here on SB about my Scuba Force SF2 class with Tom McCarthy.

The first day was fun, relaxing and yet a bit troubling. I drove up from Key Largo to Tom's parent's house in Pompano. Getting out of the door was a bit chaotic, and I had to double back for my laptop. The directions were clear, the traffic was tolerable and I was stoked when I got there. @Tmccar1 had already clued me in that this was going to be a gear and class day, so I was mentally prepared for it, or so I had thought. After all, I had read the English translation of their German manual twice and I had read both their translation of the Petrel 2 manual as well as the DiveCAN manual I found on Shearwater's site. As previously noted, I had already assembled my SF2 and was eager to get Tom's input.

The first order of business was for Tom to pull my rebreather apart and test everything. Everything. He carefully explained things as he went along, being sure to clue me in on the workings of the four isolators. Somehow, I had gotten everything assembled correctly, including the dil and oxy tanks on the correct sides. He even liked the M8 x 1.25 knurled knob I had gotten to replace the boring wing nut that comes with the unit. Instead of bringing the teacher an apple, I brought him one for his SF2 :D :D :D

61Bi-qfJBdL._SL1181_.jpg

I'm a gear head, first and last, so it was no problem for me to pay close attention to everything uttered by Tom. It's obvious that he really understands this unit and every feature completely. So then, we proceeded to scrubber packing, unit assembly and testing. Tom not only teaches you how to do this, but why you should do it in a particular manner. I believe in having printed checklists for rebreathers and the manual didn't have one. Fortunately, Tom had a great one prepared for me. I had already started developing one in my head, but this one was far better and followed in a logically progressive manner. I won't have to reinvent the wheel here!

After an excellent lunch, Tom really blew my mind.

During the afternoon, Tom did his level best to baffle me with various scenarios and dry drills. I had been trained on a rEvo and a GEM, neither of which were an eCCR. Consequently, I really had to expand my mind to encompass the additional failure possibilities I could encounter as well as to meet Toms high expectations. He hit me with hypercapnia, hyperoxia, hypoxia and boom drills. As soon as I thought I had it, Tom added another wrinkle. I thought I understood what the isolators were for, but by the end of the afternoon, I KNEW what they were for. It was the most intense session I've ever had. It would be eclipsed over the next few days, but up to that point it held the superlative.

Don't misunderstand... this was not a hazing. When I didn't understand something, Tom methodically and patiently explained it in a way that most anyone could understand or he lead me through a discovery. That didn't stop him from being relentless and keeping me on my toes. I really liked the discovery method and am glad that it was continued through the class. It's one thing to be fed an answer. It's far better to figure some of it out on your own. To be frank, there were some parts that I should have known, being a CCR diver. I just don't think it was covered in my previous class. In fact, I'm pretty sure of it. That was the troubling part of the day. Importantly, I know it now and I have Tom to thank for that. Troubles be gone!

That evening I was treated to an awesome dinner and then Tom and I did the classwork and Power Points in the living room. We checked the weather, and the seas didn't seem appealing in Pompano or the Keys. It was decided that we would scoot up to Blue Grotto in the morning to continue the diving portion of this crossover. I was exhausted and slept well. It was a great day.

This is awesome - looking forward to your next installment! :)
 
Day 2: Feeling a bit flush

Being early risers, Tom and I were up early and out the door. We grabbed Sprinter van and body fuel on the Turnpike. Tom is an easy person to travel with and even easier to talk things over. It was good to get to know him on the 4+ hour drive to NCentral Florida. We agree on a lot of issues concerning training and such. He knows that above all else, I want to make sure my trim and buoyancy are spot one. I've got a rep to protect! :D

I think it's really important that the student's and teacher's attitudes and expectations mesh well. Even before we started training, I was confident that Tom and I were simpatico in that regard and the trip only confirmed it. He knows that I'm a perfectionist where it concerns gear issues. I'm constantly evaluating how gear functions and if there is any reason or method to improve it. Take the o-rings. The tolerances are so tight, that it's hard to pull things apart. Separating the head from the tube is problematic because there's just so little to pull on. It separates easy enough lower down, but that only complicates the process. Tom and I are bouncing ideas off of each other about this. We'll see what we, or others, can come up with. For now, we just use patience, persistence and a lot of elbow grease.

We got off the interstate about 11:15 and picked up Subway. I made the mistake and got a diet coke. I get cramps when I drink too much caffeine. We ate in the van and arrived at Blue Grotto. Check in was easy and I have to say, I'm still impressed with the place. They've done an awesome job all over. There were a few classes, but only one was OW. That meant that the visibility would be sort of clear and it was. We were told that they doubled the speed of the pump that pulls the water out of the basin so it clears up even quicker now. I like that.

Once we were parked, we did the final builds and went through a meticulous pre-dive check. This is probably the most important part of diving a rebreather. If you are reticent about doing these checks then rebreathers just aren't for you. Tom was pretty thorough about each step, and did not assume that I understood any of them. I demonstrated and he accepted or corrected. We repeated those steps until I really understood it and had it right. At the end of it all I pinched my nose and pre-breathed the unit for five minutes before heading down to the water.

Splashing was pretty uneventful. One of the great things I love about this unit is that the CL (Counter Lung) is out of the way. I hate CLs on my chest. They just seem in the way and interfere with how I like to dive. The SF2 allows me to suit up easily with nothing in the way of putting on my fins or clipping items off to my harness. Tom liked the way I married the SPGs to the MAV (Manual Add Valve) with a slice of inner tube. It makes finding everything easy. I have to admit flailing a bit as I got used to the balance of the unit. It felt kind of wobbly even. Buoyancy was easy enough to attain but I felt my trim was off. Moreover, I felt like my breathing was kind of hard. Then there was the honking. I have to admit that I was feeling a bit overwhelmed by the newness of it all. I mean really? Have I made a mistake with this unit? I was only ten minutes into this and I was about to call the dive. Instead, I met Tom for a brief conversation in the underwater "breathing dome". I expressed my concerns and Tom gave me some insight. First, I was a bit head down, which would affect my breathing. Second, the honking was normal while the shroom valves were breaking in. Changing how I breathed might eliminate the noise. Da-yumn! He was batting a thousand. My anxiety dissipated as I employed his suggestions. This was nice... but I had about two more hours to kill in this grotto. I needn't have worried.

I spent at least thirty more minutes simply getting used to the unit. I was having a bit of difficulty with my buoyancy but I was getting better. Tom started a game of rock Jenga on a boulder which really helped me to relax. Then, just as I was relaxed, Tom started hitting me with underwater drills. I would barely finish one and he would be giving me another. I sometimes had to pause him out so I could get my unit back to normal. BOOM! Hypercapnia! Hypoxia! Hyperoxia! Chipmunk Cheeks! Dewatering exercise! BOOM again! Whoa! This was even more intense than yesterday. I don't know about everyone else, but I really like this kind of intensity when my life is on the line. We explored how all the isolators worked and that they didn't affect external supplies one whit. I bailed on my unit, dove it like an SCR, plugged in external DIL and more. I swear I did so many DIL flushes that I felt like a toilet in Grand Central Station! Then it was time to stress me out on buoyancy and trim with line drills. I was pretty happy with buoyancy and trim and this seemed to work out well for me. But then I got light. No prob and I blamed my technique. I tied off my line on a rope and as I turned, Tom gave me the turn signal. So I pivoted again, grabbed the reel and as I faced Tom, he gave me the OOA sign! I dropped the reel, passed off my bail out bottle, and took his. I picked up the reel and followed him out. He wasn't satisfied, so he gave the OOA signal again and once again swapped bail outs. Now I was real floaty and I was having a hard time recovering with so much going on. No more air in my BC, so dumped out my nose... several times. Obviously unhappy that it was horrible, we did it again and it came off without a hitch. Whew! We swam over to the Jenga pile and after a few minutes, I showed Tom my DIL SPG. After a bit over two hours, it was time to call the dive.

I was exhausted. Tom made me bail out to the surface. I seem to forget to change from CCR to OC on the Shearwater when I do. I didn't this time. (To be continued)
 
Day 2: Feeling a bit flush
(continued)​

Exiting was anti-climatic which is good. Rather than make two trips, I walked up the ramp with all my gear. I had worn a shorty, but I was feeling just a bit chilled after the 2+ hours at 70F. Tom was a bit perplexed as to how much DIL I went through. I got dry and then started disassembling the unit. That's when I finally heard the leak. The ADV (Automatic Diluent Valve) had a tiny leak. I could hardly hear it on the surface. No wonder that my buoyancy was off. We thought back through the training. I had checked for leaks during my boom drills, so I know it wasn't leaking then. I had felt like I had gotten the unit's buoyancy mastered at one point too, so I'm sure it wasn't leaking then. I imagine it developed that heinous leak as I was running the reel. The good news is that it's the guts out of an Apeks second stage, so it will be easy to adjust.

There were a number of things I really like about diving the SF2 that weren't apparent on the discovery dive I had done months ago. It's way easy to do DIL or Oxy flushes. Way, way easy. I have no idea how many flushes I did in the grotto, but they were easy and quick compared to the other units I have tried. Just put your head up and smile. You can hit the MAV or simply go upright and let the ADV do it for you. Check those PPO2s and you're done. In addition, it's super easy to check to see how much loop volume you're working with. Just reach back and stick your fingers up the back of the tube that houses the CL. You can easily feel how close it comes to the end. One or two breaths and you know where you're at empirically. No guessing! On top of that, dewatering is amazingly simple. There are a few ways to do it. I prefer to close the loop, go on bail out, get upright and hit the MAV 'til you fart. You're done! Since the loop is floating straight up, you've gotten all the water out of it as well. Roll backwards just a tad, and grab the loop. Easy as pie. Finally, and I'm sure I'm missing a few, it's easy to feel how your trim is doing by how you breathe. No, it's not excessively hard to breathe with your head way down, nor will you have massive chipmunk cheeks going straight up, but it's intended to be horizontal for the most part. Since I love being horizontal, I'm way OK with that.

The trip back was full of contemplative discussion. It was good to bounce things off Tom and listen to his insights. He has a wealth of experience on rebreathers. He was pretty positive about my performance in the grotto. I felt good about it, but I certainly knew I had improvements to make. Lots to do in the morning and a number of miles to put behind us this night.
 
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