With the I.D.I.O.T completed and with waterproofing tested in shallow and fairly deep (80 ft) water, it was time to go take it for a spin in “the deep”. The (purposely) sunken boat in Hathaways ponds seemed like the perfect place to go- there’s stuff to see, and places to swim.
The logistics of a “deep” oxygen rebreather dive were not as simple as one would hope. Since the counterlung is also used for buoyancy, it is not easy to accurately predict the volume needed (without prior experience). It is also hard to descend when you are several lbs positively buoyant. It was decided to descend on a buddies O/C and then breathe the normoxic gas from O/C into the counterlung to provide a reasonable PO2 at depth. This worked more or less perfectly, giving me a rough PO2 in the 1-1.4 range.
After completing a swim around the boat, we followed the line across the great murk of the pond to shallower waters (and lower PO2s). However, due to trying to attain neutral buoyancy some gas was exhaled, causing PO2 to increase when the loop was re-inflated. So we made a stop at the “deep” (30ft) platform to take on some more good normoxic air to bring the PO2 back down to oneish. I expected the loop to get a bit rich as I vented air and played with buoyancy on ascent.
From the deep platform we continued along the string to a shallow platform, the mirror, and eventually even found a nice (underwater) chair to sit in.
With the deep testing completed, we headed back to the beach and swapped gear so my buddy could check out the rebreather in shallow water.
Things seemed to be going well until my buddy got a taste of the ol caustic cocktail when he inverted slightly. This caused him to call the dive. Neither of us can figure out where the leak came from since on my dive there was only a little bit of water in the CL after 40 minutes. His flood was at least ~1L of water, which is a significant flood. This underscores the need for backup at all times when diving the rebreather, and this is obviously a reason why people don’t run around breathing off of a single AL6 all the time.
Blowing up my rebreather 😦 + performance notes
I’ll start with the exciting part- performance. I used about 800 PSI from my AL6, which is about 1.6 CF of oxygen for a ~45 minute dive. This was supplemented by 2-4 big breaths from O/C, which would be about the same volume. the dive profile was straightforward, straight down to 40′ and then a slow ascent to the surface.
I was overweighted with 25lbs with my 7mm hooded vest and 7mm wetsuit with booties. This caused my trim to be basically vertical, and the cl volume needed was essentially the whole counterlung. This is because there is no huge cylinder strapped to my back during the dive, so the belt and counterlung create a huge moment on my body. This means I have to swim to stay in trim, which makes for a bit of a frantic dive. Reducing overweighting would help, but really what I need is to move the weight up to my back. On previous dives with a ~2mm wetsuit I held a rock far out in front of my body, which gave the weight of the rock enough leverage to counter the small amount of weight I was wearing. With 25 lbs, it seems unlikely that I will be able to balance that out without moving the weight.
Blowing up the rebreather was much less extreme than it sounds. I tried to dewater the flooded rebreather by pressurizing the counterlung- what I forgot to do was to open the vent, so I just popped the counterlung. Not ideal! But it should just be a matter of buying another drybag and cutting some holes to replace the counterlung.
It was nice to finally give the I.D.I.O.T a real test and to on a really interesting dive. I hope to return someday soon with my own diluent addition!
After feeling a bit like a snail in a shell in my last rebreather, I decided I wanted to make something a lot smaller and more ergonomic. Hence the next generation of the rebreather being called the Nudibranch- Latin for “naked lung”. A suitable name for a design with a scrubber-in-lung and with the counterlung unenclosed in a shell.
Improvements over i3
I knew there were some features I wanted to keep from the previous revision, and some things that needed to be improved. The materials for example, all proved to be robust and appropriately resistant to chemicals. the manual add valve (MAV) functioned well, and the counterlungs were of a comfortable volume. Scrubber duration was adequate as well. However, there were some issues with i3:
Difficult to reach gas controls
MAV hard to locate
Low gas volume
Assembly took too long
With a focus on simplifying the assembly, i4 looks and feels more like a simple rebreather rather than some kind of science project.
The main inspiration for the new design was the Drager Model 138 rebreather. This model was famously used by Hans Hass in the Red Sea and later went on to be a “sport rebreather” diving system used for leisure, re-branded as the barrakuda or medi nixie. It turns out that it got a lot of things right.
One of the interesting aspects of the model 138 is that it is mostly cloth. When working at the scale of the human body, the cost of materials and the size of parts can add up quick. The last rebreather was encased in a large aluminum shell bolted to an 80/20 frame. This frame covered the gas cylinder, as well as two 8L couterlungs. Since the scale of these parts is cm, the small offsets to accommodate things like the counterung bulkheads or the gas addition fitting took a lot of room. Wrapping that all in aluminum made the shell quite bulky. comparing the two units above, you can see that i4 is much smaller.
The breathing hose routing is a lot cleaner, since the hoses run over the shoulder instead of straight outwards. This means I need less hose length. In the future I hope to convert to 1.5″ diameter hoses that are ~6 in shorter, for lower work of breathing.
Gas Volume/Valve Access
The Model 138 also has front mounted gas, which means all the valves and controls are easily accessible to the diver. They also are not mounted on a whip/hose like on the i3. With the i3 it was possible to “loose” the MAV since it was not mounted to anything.
The i3 valve was accessible, but it was extremely challenging to reach and required flexibility. On the i4, the valve is in the front and stationary, and only requires one intermediate hose compared to the two for the i3.
I knew from my previous design that I wanted a lot more gas so that I could stay underwater longer. I still haven’t figured out the best way to reliably get oxygen fills, so I stayed with the hardware store welding bottles, but I doubled up on them. More can be read about that here.
Ultimately, the only real issues I had with this design were MAV related. The gas regulators seem to restrict the flow far more than the old regulator, which makes the counterlung fill very slowly. It also seems like they cut off at a higher pressure, leaving a significant amount of gas left over in the tank. This makes buoyancy and breathing comfort a challenge, and limits range. However, twice as much gas is twice as good, and dives up to 45 minutes have been conducted without complete gas exhaustion.
Counterlung material selection and design
This is really the complicated part, and its particularly fraught since it is where all of the rebreather magic happens. The bag must be, relative to the demands of the dive (duration, pressure, volume of bag) completely watertight and made of a waterproof material. Some leak rate is permissible, but it has to be low. In order to capitalize on pre-existing materials and advanced technology, I decided to use a drybag. The other options are to sew a bag and seal it, heat seal a bag, or sew and completely impregnate a bag with silicone.
Sealing the end of the bag
Since I managed to find an appropriately sized drybag, I ended up just buying one. Testing of several bags revealed that the stock roll-top seals of dry bags are inadequate. Specifically, the way that most of them close is by clipping the ends together and rolling them shut. While this is fine for splashes or even putting it ontop of water, submerging the bag will squeeze the air out of the wrinkles created by bending the rolled up seal.
Without bending the seal, it is possible to get good enough contact between the two sides of the bag that it will form an airtight seal. However, the particular bag I chose had stiff mounting points for the buckles- these interfered with collapsing the seal in that area, and provided a leak path. Absolutely fine for a drybag, but not good enough for a counterlung.
By removing the stiffener and making some aluminum clamps, I was able to seal the bag well enough. I flipped the bag inside out so the smooth urethane coating was on the inside of the bag, instead of the textured nylon surface. Additionally, it is important that the bag material was very thin so the seam in the material does not disrupt the seal.
This is really a dream for scrubber access and drying since the whole lung can be rinsed and turned inside out to dry.
Making holes in the bag
I knew there would need to be at least 3 penetrations into the bag- inhale, exhale, and gas add, in addition to the large hole in the bottom. all of these of course, are leak paths!
The inhale and exhale penetrations are sealed with these (put link here) handy PVC bulkhead fittings, which conveniently fit a piece of 3/4″ pipe stub on one end to attach the breathing hose. Instead of the stock gasket, I used an oring and a retaining groove. The gaskets that were provided may have worked, but I wanted to be sure that I could get good contact along the whole circumference. The provided gaskets had a rectangular cross section and were hard- requiring a lot of force to seal. The replacement orings are soft, have a reduced cross section, and a much finer surface finish.
As you can see in this diagram, some water is actually allowed into the bag via the threads on the bulkhead fitting, but it is stopped by the oring and the glue on the bulkhead.
The other hole is a standard dump valve/BCD inflation port. These were “successfully” used on the i1 and i2 rebreathers- successful in that they did not leak, less successful in terms of actual diving.
The last (and yet tested) item is the drysuit exhaust valve/ overpressure relief valve. Once installed properly, this should help avoid over pressurizing the lungs on ascent. Its stock cracking pressure is adjustable between 3-10″ H2O, but by modifying the spring spacer I bumped it up to 8-16″ H2O. This is probably the leakiest of all the valves because it requires a large hole- a larger hole is harder to seal because the seal is longer. Usually these are installed with a sort of large rubber washer with a C-cross section. The material the seal is attaching to goes in the open part of the C, and the washer is glued in. Since I don’t have that washer, I haven’t installed it yet and I have been avoiding overpressure via the “oro-pharyngial” valve.
Intensive leak testing (more here) allowed me to validate the design before committing to a whole build. That was important, because a lot of things did not work initially. For example, I couldn’t apply enough torque to the brass thumbscrews to seal the bag, so I had to switch to a nylock nut. Another example is that the original gasket for the bulkhead seals was determined to be inadequate.
Just like with i3, the last thing I was really prepared to deal with was attaching this to my body. Unlike the i3, I knew that this challenge was coming. I considered something like a vest a la model 138, but that would require buying a few yards of fabric and knowing what to do with it, and getting a sewing machine. Instead, borrowed some inspiration from an oxydiver design (link) and backplates and designed in slots for a hogarthian harness. In the end, I actually think this is better since it is now compatible with all kinds of 2″ webbing accessories.
Of course, there is no backplate, and the gas is mounted on the front of the diver. After playing around with a bucket of sliders and clips I came up with a simple loop around the two canisters, with a 2″ long loop at one end to put the waist strap through.
This rebreather is actually very fun to dive. I would actually consider diving this over OC on shallow dives. However, no project is ever perfect. The three things I will likely seek to improve in the inevitable i5 are:
Terrestrial O2 regs rust and fail. O2 is expensive in small disposable bottles, and having a million of them around is silly. There is also no SPG. Normal scuba cylinders and regs are far superior.
No place to put an inflation cylinder for drysuit. Even in 20′ of water I think I would prefer a drysuit over wet- especially if I were to dive in the winter.
People say YERGONNADIE if you dont know your PPO2. There is some merit to this claim, but I feel it is not likely if you respect the depth limitations of an o2 rebreather.
A lot of these changes or issues have implications- if you have an inflation cylinder, why not make it breathable as backup? If you add oxygen sensing, why not add that breathable cylinder as dil? If you give an engineer a cookie…
Filter Cafe was second on my “outliers” tour. It was near a train stop, but one that was relatively out of the way- Dupont Circle on the red line. After a lovely train ride and eventual departure from the air conditioned bliss that is the D.C. metro, I hoofed it a few blocks to Filter Cafe which is situated in what amounts to a back alley off of the main street. It is bizzare street- just back entrances to buisnesses (dry cleaners and the like) with people smoking on them, then a small coffee shop.
Filter Cafe would be at home on Newbury Street in Boston. It shares a lot of architectural themes that you find at places like Wired Puppy or Sofa Cafe, which is to say it is a garden level shop with a few patio tables out front, with a long, brick lined interior containing few tables. It even has a bay window as an entrance. Unlike Boston, it was still insanely humid and hot and I arrived to find it full of people seeking air conditioned asylum there, so I had to sit outside. Also, Newbury street is not a back alley.
Since I got there in the afternoon, I was compelled to order a pour over (no drip coffee is available in the afternoon). Like Newbury street, this was expensive. I opted for what I hoped would be a fruity African blend, which was served in a small cup with the Filter logo silkscreened onto it. It was black on the outside, with orange enamel on the inside. The coffee was acidic and smoky, without much fruityness to balance it out. It had a lingering minty aftertaste, but your milage may vary. Overall not a bad cup of coffee, just not my favorite flavor.
Since all thirteen indoor seats were taken, and I didn’t want to sit on a windowsill, I ended up sitting outside pondering the insanity of drinking 10 ounces of hot coffee in the brutal DC heat. Fortunately, this gave me a chance to assess the patio situation. The options were two faux-cedar folding tables accompanied by pop-orange plastic molded chairs, or a weathered white oak bench. I opted for a chair at an empty table, and hoped that someone left the inside before I finished my coffee.
That’s the whole thing! 13 seats, weird lights, coffee bar
At some point, I noticed few people leaving so I swooped in and took their seat in the refreshing air-conditioned room. The indoors is your typical long brick room, on the right there is seating, including a bench with five tables and five chairs (10 seats), as well as a small 3 seat bar with stools. The left is occupied by the coffee counter, including pour over station, espresso, and pastry area.
The chairs are red, which matches their custom printed vinyl-wrapped La Marzocco, and the bricks. The rest of the place is made of various kinds of wood stained in slightly mismatched walnut colors. The low ceiling, air conditioning, and dark wood give it a cool, underground feeling, although I bet in the winter this turns into a cozy, warm space quite easily.
The lighting was dim, contributing to the cool cave-like feel, but the upside-down glass light shades projected crazy (but totally static) patterns on the walls. The light temperature was warm from bouncing off all of the walls, which definitely put some points in the warm/cozy column.
I think one of my favorite parts was a printed poster (on plain A4 paper) that declared “My body is like a filter, coffee goes in and sarcasm comes out”. That and they also have a bathroom (possibly a legal requirement in DC).
Purveyors of “Functional Objects For All Surface”
On the way back to the train I stopped at “Tabletop” to pick up a new notebook- I had filled up my last page and I needed more space for the rest of the shops!
On my way from Slipstream to a bus stop, I ran into yet another cafe! As I mentioned, part of the rules of coffee travel is that if you see a real cafe, you have to go. And so I went.
Dolcezza is a gelato bar and espresso shop. It is spotlessly clean, and extremely cold inside. All of the places in D.C. have some kind of air conditioning, but only here was I verging on uncomfortably cold. As in, bring-a-jacket winter-is-coming cold. but it was also a relief from the humid and hot outdoors, so it was bearable.
I had an espresso shot. Unlike the rest of the country, all the esprsssos I got in D.C. were actually single shots- not double shots. Typically in Boston/LA/SF I see an “espresso” being pulled as a double shot for americanos and espressos, but in D.C. they were all just single shots.
The shot was served in a brown, thick walled espresso cup with matching saucer. Surprisingly, there was no sparkling water to go with it, although other people seemed to get some. The coffee was very acidic, with a fruity finish and a sweet aftertaste- I think it was stumptown hair bender roast.
The cafe is laid out around a long bar with gelato and coffee. A doorway protrudes into the space in the middle of the bar, creating to bays for small tables and chairs (pictured). The floor is white tile and is quite clean. Overall, it reminds me of a very clean ice cream parlor or train station. The tables are marble-esque, and the chairs are stained red wood upholstered with red leather, or wood stained to match the chairs. Both are comfortable enough.
I believe this is supposed to be an Italian styled place, and it does seem like it would be at home in the north end in Boston. It does seem like a place where you could come and comfortably read the paper or meet up with someone, but I think the gelato (which I did not try) is their real strength, not coffee. If I went back, I would have to try it.
Northside Social, or “NoSo” is out in what might be considered the suburbs of Washington D.C. It is a huge building, boasting ample patio seating, a huge first floor, and a second floor which is a wine bar (with an espresso machine). It is certainly the biggest coffee bar I visited on my trip, and it is open late because of the wine bar- this made it the ultimate destination for my day 1 trip, since I could arrive at just about any time and still expect the place to be open.
I had a cup of drip coffee, roasted by intelligentsia. I may have been a little exhausted and buzzed at this point, but I would describe the coffee as smoky and acidic, with a fruity aftertaste. It is worth noting that there are two options for drip coffee- a regular cup, and a “mug” of coffee which is two 10 oz mugs of coffee (one refill). I am impressed by how considerate and innovative they are with this offering- this is the only place I have seen something like this on the menu, almost explicitly inviting you to stay for as long as possible.
2nd Floor/Wine Bar
The inside of the cafe is tastefully decorated in coffee-drip paintings of famous actors and personages. The tables are wooden, and plentiful. Towards the back of the cafe the tables get little less uniform, but they is still a ton of seating. The second floor wine bar is decorated with more paintings, and is furnished with light wood tables and bar stools. If you look carefully, you can see Clint Eastwood in the photo above.
The wine bar was equally as inviting and as accommodating as the coffee bar. I ordered a highly modified and delicious grilled cheese for dinner, while I made some notes on my trip so far (pictured above).
Slipstream was not on my original list, but as I was headed to compass coffee on day 2, I passed it. One of the rules of coffee travel is that if you come across a decent looking cafe, you must go- so I went!
It turned out to be a great decision. First off, I was hungry, and their breakfast food options were much better than any of the other coffee shops I visited that day. Second, they have good coffee, as well as coffee cocktails- not something you see everyday (or ever, in MA). I was sorely tempted to try one of the coffee cocktails, but it was 8 A.M. and I had a long day of coffee ahead of me, so I opted for my gold standard of coffee comparison- a cup of black drip coffee.
toast for breakfast
The coffee is apparently roasted by “Madcap Coffee” and it is balanced between sweet and acidic. It is not unlike el gallo blend, but it is balanced instead of acidic. It was served in a notneutral lino coffee mug, which is actually a fairly normal looking white mug.
The bar stools and chairs are a light colored wood, while the tables are stained a dark walnut color. I think this brings attention to the weighty tables, over the chairs, which are comfortable but unremarkable.
The back, under the skylights
The lighting is interesting and worth noting, since the place is a single large chamber that serves as both a brunch spot, a bar, and a coffee shop. It is modern and clean, with lots of glass, wood, air and light. Most of the light is provided by the floor-to ceiling windows at the front of the cafe, as well as the skylights at the back of the cafe. The rest is rather dimly lit by reflected light from the outdoors, and more indirect lighting from large domed reflectors on the ceiling. This means that there is little in the way of direct lighting, making the inside seem soft. In the daytime this gives it a cool, shady feeling, and I imagine at night it gives it a nice bar ambiance.
I am very happy that I made the stop at slipstream. I ended up with a full stomach and plenty of time left to explore the rest of the city.
Compass was my first planned coffee stop for the day. The location I visited was just a few bus stops from the Dolcezza. It is a single-story brick building packed to the gills with coffee products, seating, and what appears to be the compass coffee roasting operation.
I ordered a small drip coffee, which was made with their cardinal blend, and a saag-paneer filled pastry, similar to a bao. The pastry dough was sweet, and the sag-paneer was spicy and bizarre, but in the best way. The coffee was smoky and sweet, a little acidic but not very fruity. The coffee was served in a paper cup.
I sat at a bar in front of their coffee roasters. Like slipstream, light was provided mainly by numerous skylights and windows rather than with artificial lighting. This, combined with the brick, gives the place a warm glow. The place was pretty packed, with a long line when I arrived. But there was plenty of space inside, and I think pretty much anyone who wanted a seat got one.
As you can see in the photo, they have pretty much every kind of cafe chair, ranging from various heights of 4-legged metal stools, to orange and white metal chairs. The wood was mostly light colored pine and veneer, which was complemented by the white paint and tile. The somewhat high ceiling and skylights give it an airy, clean, and open feeling. this feeling conflicts somewhat with the general cramped mess and busyness of the floorplan.
The CCC lacks the usual signage out front, but once you get inside, it is clear that it is a coffee shop. They seem to serve intelligentsia coffee, but they also sell retail heart coffee. As one would expect, the coffee is good. The coffee was balanced, with a smoky aftertaste. It was served in an hourglass shaped diner mug, like the ones that Diesel sold before switching to intelligentsia-ware.
This shop is long!
The interior of the shop is long. The grey bulkhead that comes out of the ceiling, the rail, and the long coffee bar all help make it seem even longer, emphasizing a far away vanishing point. Their logo is three cups over two bars, which is similar to the flag of the District of Columbia. Definitely clever.
On the left side, there are small four legged stools mixed with creamsicle chairs- white on the outside, orange on the seat. These seats face each other over low spool tables. In the front of the shop there is a bar at the window, and two very expensive looking tables with matching benches. These feature a dark wood tabletops, metal frames and narrow benches. It was a surprisingly comfortable spot to sip my coffee and read my book.
Peregrine next to NOT Peregrine (La Pain Quotidien)
Peregrine Coffee was the first stop on my coffee tour. It seemed easy to get to form the Hirshhorn and it would be my only stop out on the east side of DC. I arrived at about 4:00, drenched in sweat from my two-block walk over from the East Market stop on the Blue Line. Say what you will about the heat on the west coast, but at least it is a dry heat!
This location is located right next to a non-peregrine cafe. I was almost lured into buying coffee from them but the brew-o-matic and lack of coffee menu made me think twice, and check outside. Sure enough, Peregrine was right next door.
Since it was about 90 degrees and humid, I opted for a smaller espresso instead of my usual small black coffee (the real standard for judging a coffee place). I also ordered a ham and cheese pastry.
The pastry did not inspire any real confidence in me, with its single roll of ham and sparse cheese, but I devoured it anyway since I was hungry. It was decent-edible but not a reason to come back. Eventually my espresso was up (after a mix up that almost landed me with a macchiato).
The coffee on the other hand, was short- by that I mean it was a single shot of espresso. One unusual thing I learned is that in DC, espresso is normally a single shot instead of the doubles you find in Boston and LA or SF. Overall I was happy with the coffee. It as fruity and the acid was fairly balanced. They clearly have some idea of what they are doing over there with their machine and their counterculture coffee (they also have a house peregrine brand). It was served in a standard white saucer/espresso cup/spoon, along side what I assume was supposed to be sparkling mineral water in a libbey druatuff glass. Unfortunately this turned out to be lukewarm water, which was trumped by the free ice water they were also serving.
Pear Eh Grin
The decor was cute, but not in a way that stands out. It felt like it was new and nice, and organized. Inviting, but not too exciting. They did have a funny rendition of their name on the wall (pictured above). There is interior and exterior seating available. The inside consists of a small square of tables in the front (about 4 people/table), a bar for seating for three, and another line of tables going back to the back of the cafe, each seating two. Next to the line of tables is the coffee bar, including a pastry case, espresso machine, and retail area. This cafe (like the rest of the ones in DC) also boasts a restroom. Outdoors there are five tables that can probably seat three people each.
Nice, clean, but not exciting
The tables and chairs were a light blonde wood, probably pine. The outdoor furniture is metal painted that rustoleum-lawn-furniture-green. The counter echos this theme with a light wood and glass construction, giving the whole place a friendly (but not enlightening) interior.
Line for days! If you want coffee, you can probably skip it
When I arrived at Baked and Wired, after a bus and a schlep down 30th street, I was extremely unenthused to find a line out the door. What I did not know was that Baked and Wired is one of “those places” where people queue outside in 85 degree heat to buy expensive and trendy pastries. There is nothing wrong with that, but typically this is not my scene. I typically prefer a spot where I can grab a quick cup of coffee and a seat and spend a few hours lost in a book, writing emails, or pretending to be productive in some other way.
The coffee bar, featuring finger
Once I was inside, I realized that it is actually that kind of place, or rather half the store is that kind of place. There are actually two totally separate counters inside, one for coffee and one for baked goods, which form a delicious symbiosis. From the bakery, I purchased a pistacio cupcake. From the coffee bar, I bought a cup of coffee.
The coffee was acidic and a little fruity- a nice sharp note compared to the creamy sweetness of the cupcake. And unlike most cupcakes, this one had little nut-nuggets in it to add a nice texture. Together, the two of them made a lovely afternoon snack. Alone, I think the coffee would have still been drinkable, but the cupcake certainly enhanced the experience.
Blurry, but you get the idea. ft. finger
The decor could best be described as mixed. The coffee bar area has no seating. The bakery is standard contemporary-cute and displays cupcakes under glass beakers. Down a few steps from the bakery, there is a massive shell-shaped couch that faces an american flag.
In the back, things get real weird. Napinks are attached to napkins with baked and wired stickers in what must be a fire marshalls nightmare. Somewhere under all the napkins, I am sure there is a wall with more napkins attached to it via stickers. Each leaflet in the strata is marked with a thoughtful doodle or a few words.