Imre Jonk

Tandem freefall

2025-09-23T00:00:00+02:00

What is a really cool thing to do when you turn thirty? Jumping out of an airplane, of course! The most accessible way to experience the thrill of freefall is a tandem skydive. At Hilversum Airport (EHHV), about 27 km or 15 NM southeast from Schiphol, this is only possible for four days every year. Two of those days were last week. Thursday was too cloudy for flying, but luckily I booked Friday. Skies were clear, it was a warm 25 degrees Celcius, with some 20 kts of wind from the south. Perfect conditions, in other words.

Tandem jumps require more elevation than solo or static line jumps. This is because the parachute is bigger, taking more time to open. The 6000 ft (1800 m) that Skydive Hilversum normally jumps at is simply not high enough for this. 6500 ft above the aerodrome is where Amsterdam CTA East 1 begins, and it is busy class A airspace. Last Friday was one of the few days where parachuting was allowed in a column of air up to 13000 ft (3900 m) above the aerodrome.

Skydive Hilversum is an association with some 160 members. The chairman was busy checking in all the skydivers and arranging liability waivers for the tandem jumpers. I would go up with three other tandem students, all of which were first-timers. I had the opportunity to speak with two of them in and around the hangar: a guy who just turned 50, and a kid who just graduated high school. They had us fit olive green overalls in the hangar and clear out our pockets, and this is where I met my tandem instructor, Marijn.

Marijn is not just an experienced skydiving instructor. He is also an air combat controller, stationed at Air Operations Control Station Nieuw-Milligen, and is a PADI Advanced Open Water Diver, just like me. Obviously I had to talk about his work surveilling Dutch airspace, routing aircraft for training missions and deploying F-35 figher jets to intercept Russian bombers in NATO airspace. And I wanted to know all about his digital wrist altimeter, which kind of resembles a dive computer with a built-in logbook and GPS capabilities.

There was less preparation needed than I expected. It was just getting to know Marijn, who fitted, tightened and carefully checked the harness I would be wearing, as well as his tandem parachute set. He clipped a pair of goggles for me on as well. I think having a chat and witnessing this professionalism is quite important for building trust, which is nice if you're depending on someone else for your safety.

I got to the airfield quite early, which allowed me to witness multiple plane departures and parachute landings. The colorful canopies were a nice sight on this beautiful day. I said goodbye to my family and stepped inside the van that would take us to the airplane, which was being topped up with avgas at the fuel station.

The airplane, a Cessna 208B Grand Caravan with registration PH-JMP, was rented from Skydive Teuge for this occasion. It has a massive propeller on the front, systems for supplemental oxygen inside and a big sliding door on the left behind the wings. The passenger seats have been replaced with two benches positioned along the longitudinal axis of the plane. I stepped on a beer crate, climbed inside and was instructed to sit near the cockpit on the right hand side, in front of Marijn. He attached my harness to the airframe using some kind of safety cord and explained how I could take off this "seatbelt" in an emergency. The plane quickly filled up with skydivers. This is also when I met the fourth tandem first-timer, who was looking a bit pale and didn't speak much. He and his instructor would be the last to leave the airplane, Marijn and I second-to-last.

Climbing up to 13000 ft took about ten minutes. The plane flew towards the southeast until reaching about 7500 ft, then turned around. We could see the Loosdrechtse Plassen nature reserve, Utrecht with the beautiful central train station and Dom tower, Amersfoort, Almere and of course Amsterdam with the IJ river. Marijn used this time to attach my harness to his tandem kit, double-check everything, explain the exit procedure ("hold the shoulder straps, push your chest forward, keep your legs together and lay your head on my shoulder") and point out things on the ground. He could see on his altimeter how much further we would have to climb. I noticed one of the solo jumpers had a small LCD display on his parachute that read "STUDENT" with a small button next to it. Marijn explained that this is an Automatic Activation Device, a dead man's switch that automatically activates the main or reserve parachute deployment sequence when it senses that the skydiver is descending too fast through low altitude. It has different modes depending on the experience level of the skydiver. I find these safety-enhancing systems fascinating, and I never expected to find this kind of high-tech, pyrotechnic stuff on a parachute. Another surprise came in the form of an audio altimeter that was built in to the helmet of the tandem instructor in front of me. He explained that it would tell him when it came time to break off and open the chute, which could be useful for instructors or formation jumpers who are too occupied with other things to look at their wrist altimeters.

The plane made a final turn just north of the airfield towards the southwest, then reached 13000 ft. The door was slid open and the solo jumpers disappeared beneath the airframe. Each exit made the plane pitch up a little, prompting the (auto)pilot to pitch down in response. I cracked a final, slightly nervous joke about not having seen any catering on board this flight and needing to get down quickly for some snacks. It was time to jump!

I had anticipated a slight feeling of panic when the door opened and we would have to make our way towards the exit, but there was none of that. I mostly felt excitement. And a bit of awkwardness, since seat-shuffling all the way through the airplane looked very silly in my mind. I was just happy that the woman with the helmet camera had already jumped out. Then, at the door, Marijn had me dangle my legs over the edge, straight into the windstream. I assumed the exit position, and then we just tilted forward and fell down.

The first two seconds or so were probably the scariest. You get that stomach drop feeling as if you're in a rollercoaster, except you're looking at nothing but the ground some four kilometers below you, no track in sight. It's all very unnatural. Air rushes past, and this rushing sound grows more intense by the second. It takes skydivers ten to twelve seconds to reach terminal velocity. Once it was safe to do so, Marijn tapped my shoulder to indicate that I could tilt my head forward and extend my arms, and a 50-seconds freefall ensued. I was wearing my goggles, but the air molecules smashing against my face had me think that maybe I had lost it during the exit. The fact that I could still "normally" see the ground speeding towards me reassured me in that regard. The freefall was an amazing, adrenaline-fueled experience. I could clearly see the city of Amersfoort and pointed my finger at it, since hearing each other was impossible with all that air rushing past us.

Marijn brought his left hand in my field of view, counted down from three, waved his hand and triggered the main canopy opening sequence. The parachute cells filled with air and the parachute opened as designed. Parachute cord stretches a bit, but the rapid deceleration still caused us to experience quite a jolt. I equalized my ears. We could speak again, and boy, was I eager to declare that freefall is way better than I expected it to be! Nothing beats this kind of thrill. Marijn mentioned that skydiving can be quite addictive, then promptly handed me the brake loops.

My first two turns were, as can be expected, careful. But I had earlier been watching skydivers performing all kinds of stunts with their parachute, so I wanted to try that as well. I pulled hard on the left loop. We swung up, going from vertical to almost horizontal. Then, I tried the right loop, pulling even harder this time. This was lots of fun, but we were still quite high and we had a 20 kts wind to deal with. If not compensated, we would overshoot the airfield and land in a forest area. Not ideal. Marijn instructed me to turn towards the south, towards Utrecht. Looking straight down, I could see that our ground speed was exactly 0 kts. We were essentially hovering over a point below, slowly descending. I turned again to follow the tandem before us, and handed the brake loops back to Marijn for the landing.

The target was an orange flag, which was useful because it could be used to judge the wind speed and direction as well. We flew a little left-hand traffic pattern (downwind, base, final) and Marijn instructed me to lift up my legs for a bum-landing. My family was nearby and managed to capture the landing on camera. I thanked Marijn for the amazing experience and we took the van back to the hangar. I had a drink with family in the airport cafe afterwards, and they surprised me with a dinner in a restaurant in Amsterdam to celebrate my first skydive, my new job, my sisters engagement, and my father figure's 70th birthday. A very special day indeed.

My next skydiving goal: doing backflips and falling through a fluffy cumulus cloud, just like this guy.

Download

posing for the camera
olive green is the new black, 563 kB JPEG

putting on the harness
gearing up in the hangar, 2.8 MB JPEG

chatting with Marijn
"So you're MilATCC, that's pretty cool", 497 kB JPEG

a butt-ery smooth landing
"Rico! I said kiss it!", 37 MB WebM video

beer after skydiving
I think I managed to light my sister's curiosity for parachuting, 495 kB JPEG

internet linguistics

2023-04-02T00:00:00+02:00

Language is a wonderful thing. The internet is also a wonderful thing. But what does the word 'internet' really mean? The Cambridge dictionary gives this definition:

"""
internet
noun [ S ]
uk /ˈɪn.tə.net/
us /ˈɪn.t̬ɚ.net/
(informal Net)

the large system of connected computers around the world that allows people to share information and communicate with each other
"""

But the Collaborative International Dictionary of English says this about it:

"""
internet (ĭntẽrnĕt), n. A large network of numerous computers connected through a number of major nodes of high-speed computers having high-speed communications channels between the major nodes, and numerous minor nodes allowing electronic communication among millions of computers around the world; -- usually referred to as the internet. It is the basis for the World-Wide Web.
"""

One word, two definitions. One is about the internet, the other an internet. The latter implies that there can be more than one internet. And this makes sense, because the essential components that make up the internet can be used to create another "network of networks" that is disconnected from the internet that served you this article.

...and there is our problem. If we have two separate internets, which one is the internet? Well, the people who were coordinating the transition from ARPANET, the precursor to the internet that was funded by the U.S. Department of Defense, to the internet we know today, recognized this problem. They maintained a clear distinction in RFC's 871 and 872. Definitely check out the latter for a nice Winnie-the-Pooh excerpt. Anyway, an 'internet' was a network of networks, and the 'Internet' was the large network that all those universities and military installations were connected to. This use of capitalization was not just common in the protocol pushing circles. The Associated Press and New York Times for example only formally switched to the lowercase style 'internet' in 2016, the latter stating that such a change is common practice when newly coined or unfamiliar terms become part of the lexicon (see It's Official: The 'Internet' Is Over, archive).

This again makes sense. Why bother with special capitalization when everyone is familiar with it and can agree on what it means? And so, in most of the English-speaking world, we now write 'internet' in lowercase. I've been living in Amsterdam all my life, and although most waiters and bartenders here somewhat lazily assume that I'm either an expat or a tourist, the newspapers here are written in Dutch, and the newspaper companies have their own style guides. The Volkskrant for example made the change from 'Internet' to 'internet' between 26 February 2000 (archive) and 4 March 2000 (archive). The NRC switched between 15 April 2000 (archive) and 26 September 2000 (archive). A whopping sixteen years ahead of the AP and New York Times!

And the Government of the Netherlands? There have been some inconsistencies in the past, take for example this official parliament document from the minister and state secretary of finance, published on 13 April 2000. The document uses 'internet' and 'Internet' interchangeably. And this is to be expected, because as our Government changes frequently (at least once every four years), it is likely impractical to maintain a style guide like the newspapers, which often have the same editors employed for a much longer time. Nowadays though, you likely won't find any use of the old 'Internet' style in Dutch government circles.

One special (and definitely more stable) member of our Government is the monarch. The royal family has an archive of official documents, and one recurring speech that can be found in the archive is the yearly Speech from the Throne. The very first one that mentions your favorite time sink is from 19 September 2000. Interestingly enough, the original Dutch version uses the lowercase 'internet', while the English translation writes it as 'Internet'.

One final thing I want to dwell on are announcements from governments like those of Russia, declaring their intent to create an autonomous 'Russian internet'. China's Great Firewall and geo-blockades that have been a part of the internet for a long time are more examples of cyber-balkanization. Even though we are connected to the same internet, yours may be very different from mine. If you look at it this way, spelling 'internet' with a capital I is just silly.

P.S.: in the Netherlands, we refer to electronic mail as 'e-mail', not 'email'. Email has a very different meaning here. You can reach the author of this website by both electronic mail and regular mail, although the latter is not so regular anymore.

Scuba diving at Marsa Shagra

2022-07-17T00:00:00+02:00

I spent the last week in and around the Marsa Shagra ecolodge near Marsa Alam, Egypt. Like many people this was my first "far away" holiday since the COVID-19 pandemic. I had visited Marsa Shagra twice before, during my diving vacations in 2017 and 2019. The beautiful house reef, friendly staff, easy access to a number of great dive sites like Elphinstone and the amazing food made me come back again. Everything about this vacation was perfect. Well, except for the flights to and from Marsa Alam.

You can find some pictures I made at the end of this post.

Airport shenanigans
Diving at Marsa Shagra
Accommodation and food
Things to do on the last day
Airport shenanigans, part 2
Downloads

Airport shenanigans

Not many planes land at Marsa Alam International Airport. In 2017 I could get a direct flight both ways with Transavia, but sadly they cancelled that route a couple of years ago. The only service between Amsterdam and Marsa Alam has been operated by TUI Fly since then. I remember from my flight home in 2019 that the flight was delayed and that I arrived around 02:30 in the morning. The experience was worse this time. The planned itinerary was a direct five-and-a-half hour flight to Marsa Alam, and on the way back the plane would land at Hurghada to disembark passengers with destination Hurghada, unload their bags, load the bags of the passengers who just finished their vacation there, board those passengers, and fuel up the airplane for the five hours and fifteen minutes flight home. But things didn't go exactly to plan.

On the day of departure I received a text message from TUI Fly that the flight would be delayed by almost four hours. I was still home so I just turned around and got a bit of extra sleep, but was sad that now I would miss the afternoon there. An afternoon that I could have spent snorkeling and meeting new people. Later that morning it became clear that the flight would no longer be direct. The plane needed to land at Hurghada first and change the crew there. I would eventually arrive at Marsa Alam at 21:03 that night, five hours and thirteen minutes after the planned arrival time. The captain said that wind shear at Tenerife was the reason why the airplane could not make it to Amsterdam in time, and apparently TUI decided not to operate another airplane instead. Ah well. At least I can now find out if the European Flight Compensation Regulation is any good.

Customs at Marsa Alam demands a valid visa, which you can buy for €24 at the bank office just before the customs booths. Don't buy it from one of the hustlers in front of the bank office: one of them charged me €32 once. The customs officers also wanted a filled-out declaration form. Although I was told by TUI Fly that the online application, which I had completed a week before, was sufficient, the customs officers still demanded the paper form. Afterwards my passport was checked again (probably by a senior officer), and then my bags were X-rayed.

Tip: don't do the online application. The form is incredibly broken. It presented me with numerous errors, I had to fill it out again multiple times, and at one point it even presented me with someone else's information. The paper form can be filled out in a few minutes, is more secure, and always works.

Once outside the airport building I spotted the Red Sea Diving Safari chauffeur and my vacation had finally begun.

Diving at Marsa Shagra

The six-day diving package I had booked included two supervised dives in the house reef. I had made many dives there before, but it was nice to have an instructor available that I could ask questions and practice things with. My last dive was three years ago, after all.

I brought my own 2/3 mm full wetsuit, mask, dive computer, dive light and diving socks. From the equipment room I rented a buoyancy compensator, a regulator set, fins and a surface marker buoy (SMB).

An SMB prevents the boat captains of Marsa Shagra from accidentally hitting divers that are just below the surface. Each buddy pair is required to have at least one SMB, which must be used when surfacing outside of the bay's "safe surfacing area". There is a rope system in place to guide divers to this area, but anyone who wants to explore the outer regions of the (quite large) house reef has a chance of finding themselves low on air at one point. And when that happens, you better begin your safety stop and inflate the SMB. Even better is to have each diver bring an SMB, so that they can safely surface in case they have lost their buddy. The boat captains of Marsa Shagra keep a lookout for any SMBs and, once spotted, will pick you up shortly. They plan their pickups according to the dive plan that you or your buddy file on one of the two (North or South) dive profile boards.

The equipment I rented was in good condition. Together with the dive instructor I made a rough estimate of the amount of weights I would need. The last time I used six kilograms, and a quick check at the beginning of the dive determined that this was enough to get me to sink below the surface. As the dive progressed however, it became clear that I was carrying a bit too much. I had to inflate my buoyancy compensator quite a bit, causing my shoulders to float up and my legs to drop down, which required more effort to stay horizontal and streamlined in the water. I did another weight check during the safety stop. At the end of the dive, when the cylinder was lighter, I deflated my buoyancy compensator completely and found myself sinking like a rock. This was even stronger evidence that I carried too much lead. On the second supervised dive I only brought five kilograms (three on the belt, two in the buoyancy compensator pockets), and this turned out to be more suitable for me.

I would do two more house reef dives that day. The first one was together with one of the Swiss guys I met during the supervised dives, the second one was a night dive together with a Belgian diver.

Night dives in the summer are best done from 19:00 until 20:00. You will still have a bit of daylight when entering the water, but things are pitch black ten minutes into your dive. You do have to remember to exit the water and wipe your name of the dive profile board before 20:00, or the dive center employees will start the search and rescue procedure.

I didn't find it hard to find someone to dive with. There is a buddy board that can probably help, but I've found that just walking up to someone who is preparing for a dive, questioning them about their plans and experience level, and asking them if you can join works really well. In total I did 22 dives that week: four days with four dives each, and two more days with three dives each.

Apart from the house reef, there are a number of diving excursions that can be booked one day in advance. Some are by truck, but all of the excursions I did were by boat. A well-known one is Elphinstone. Elphinstone is a reef some nine kilometers off the coast, twenty-six kilometers north of Marsa Alam. Its exact location is 25° 18′ 31″ N, 34° 51′ 37″ E. Here you can see hammerhead sharks, oceanic whitetip sharks, silky sharks, dolphins and, if you're lucky, even tiger sharks.

Diving on Elphinstone is quite challenging. This should not be underestimated. My first dive there was in 2017. I had the required PADI Advanced Open Water certification, but didn't have fifty dives logged back then, so the diving center had me pay for an additional guide to supervise me. During the briefing they failed to mention that the descent would not be alongside the reef but rather "into the blue", and that the maximum depth would be forty meters instead of the thirty meters that is normally maintained for Advanced Open Water divers. In short: that dive was rather stressful. Sea conditions made for a bumpy thirty minute boat ride. Only in the boat it became clear to me that we would jump into the water using what is known as a 'negative entry': a backwards fall off the edge of the speedboat, with a deflated buoyancy compensator, descending as fast as possible in order to minimize the drift caused by the sea current. I should have aborted the dive right then and there. But I didn't, probably because I felt like I would let some people (including myself) down if I did. I had trouble keeping up with the rest of the group, saw nothing but divers below me and blue all around me, and was breathing fast the whole way down. Once we passed thirty meters, my dive computer started blaring its depth alarm. We leveled off at forty meters and, despite my heightened state of awareness, I was feeling confused. I signaled to the guide that something was wrong and that I wanted to ascent. He got a good look at me, probably saw the alarmed face behind my mask, grabbed my buoyancy compensator and quickly started dragging me to thirty meters. Once there I got my breathing under control again. We slowed our ascent, saw a school of barracudas, and surfaced safely after twenty-four minutes of dive time. Once I was in the boat, the guide descended to the five meters safety stop depth so that he could offer his (now abundant) air supply to anyone who might need it. The rest of the group didn't see much more than the school of barracudas. Years later I would learn from Simon Pridmore's excellent book Scuba Confidential that my fast, inefficient breathing prevented my body from expelling enough carbon dioxide, which under pressure causes CO₂ poisoning. Its symptoms include confusion, disorientation and vertigo.

My experience was completely different this time. I had a lot more diving experience and the sea was completely flat. The briefing was thorough, the speedboat ride took only twelve minutes, the current was not too strong (we still did a negative entry), and best of all: it was the hammerhead shark mating season. The descent was swift but not too fast. It felt like I was free falling in slow motion: kind of like a skydiver, just without the speed. There was no adrenaline rush, no heavy breathing. I was surrounded by experienced divers. The guide was right below me. The descent required no effort at all: I just emptied my buoyancy compensator completely and let gravity do the rest. I checked my instruments once more. I had a bit over 200 bars of pressure in my cylinder. My dive computer wasn't sounding any alarms. At around twenty-five meters I started inflating my buoyancy compensator to slow the descent. We leveled off at thirty meters. There I saw my first hammerhead. And another one. And some ten more. I am not too good at estimating distances underwater, but my guess is that on that first dive the hammerheads came within six meters. The feeling of being so close to hammerhead sharks for the first time is that of amazement, and joy. Then I heard the muffled, unintelligible shouts of the dive guide. He was shouting in his mask, pointing to a shark-like animal swimming away in the distance. I didn't get a good look at it. The guide put his flat hand perpendicular to his forehead, indicating a shark sighting, then curled this hand into a claw and pretended to rip open his left arm. Clearly this was some vicious animal. And clearly, the guide was overjoyed to have seen it. Back in the boat he told me that he saw a tiger shark, a rare sighting in that area.

I booked the Elphinstone excursion two more times that week. The third dive was even more spectacular than the first two, as the hammerhead sharks were a lot more curious. One of them was swimming right towards me, only to turn around at the last moment. I also saw oceanic whitetip sharks underwater, and bottlenose dolpins swimming alongside the speedboat after the dive.

My buddy Aly made an amazing video of the second dive.

Not all dives went according to plan. One of the divers on the first orientation dive had a punctured inflator hose on his buoyancy compensator. This was discovered when we entered the water from the shore, but luckily the instructor was able to fix the problem with nothing more than a knife and a tie-wrap. On another dive I was practicing deploying the surface marker buoy, but while focusing on the task, I failed to notice that I became positively buoyant and that I had ascended far faster than what was recommended by Suunto's RGBM algorithm. This caused my dive computer to recommend a five-minute decompression stop with a ceiling of three meters. I witnessed two counts of mask strap breakage, one of which was my own. It broke on the boat, right before entering the water with a large group of divers. Luckily the guide had a spare mask strap that I could use. One night dive went without a proper briefing and ended in a longer and deeper dive than some were comfortable with. And on that first hammerhead dive, I exceeded the no-decompression limit by about two minutes.

A selection of sea creatures I've seen on my dives are hammerheads, silky sharks, oceanic whitetip sharks, whitetip reef sharks, bottlenose dolphins, spinner dolphins, a dugong munching on seagrass, sea turtles, moray eels, an eagle ray, an octopus, nudibranchs, highly venomous scorpionfish, lion fish, crabs, puffer fish, barracudas, whiptail stingrays, parrotfish, triggerfish, butterflyfish, Napoleon fish, sea needles, sea urchins, starfish, giant clams, Red Sea bannerfish, surgeonfish, hermit crabs and shrimp. I dived together with Egyptians, Swiss, Germans, Hungarians (they liked my name), Brits, Czechs, Dutch, Slovaks, Belgians and Austrians.

There are also people who freedive at Marsa Shagra. The dive center even has an instructor available for it. Marsa Shagra is a perfect place for freediving, with even Umberto Pelizzari having freedived there. During my stay there was only one freediver, Frederique. He dived all by himself, mostly early in the morning, with a monofin. Mornings are the best time to dive at Marsa Shagra because the rising sun illuminates the reef, and the tide is still high, which is good for visibility. I first met Frederique when I was staying at Marsa Shagra in 2017. He is from France, and gets his freediving inspiration from dolphins. However beautiful his stories may be, I think I'll stick with the (safer, easier) scuba diving for now.

Accommodation and food

I slept in a regular tent, right on the beach. I've really only used it during the night. After sunrise it gets too hot to sleep, and relaxing in between dives is best done in the cafeteria area anyway. Every morning around six I would get dressed and take a small bag with things like a towel, water bottle and my dive log. Then I would head out to the dive center, only to return after dinner, at which time the sun had been down for some hours already and the climate inside the tent would make for a comfortable night's sleep. Except maybe for the first night. That was on a Friday, and the call for the morning prayer could be heard quite some time before sunrise.

It struck me that there were some expensive cars with Egyptian license plates in the parking lot. The Red Sea Diving Safari tries to cater to the wealthy guests with the new Superior Deluxe Chalets. Complete with air conditioning, mini-fridge, Nespresso machine, 50-inch LED TV and a private terrace.

Marsa Shagra has a beautiful restaurant that is elevated above the rest of the ecolodge grounds. The view of the Red Sea, plenty of shade and always a fresh breeze make it a nice place to gather for breakfast, lunch and dinner. The buffet is different each day and the chef always tries to impress with artsy salads and desserts. There is one night a week when pizza is baked in an Italian pizza oven, on another night traditional Egyptian food is served.

Things to do on the last day

Recreational divers should maintain at least eighteen hours between the last dive and the airplane's departure time, in order to prevent decompression sickness on board. I would depart Marsa Shagra at around 13:30. I packed my stuff early in the morning, returned my rented diving equipment, and went for breakfast. This was around the same time the Elphinstone boats were leaving. One of the boats turned around, the dive guide shouting: "Dolphins! Dolphins in the bay! Tell everyone!". I saw some people scrambling for their snorkeling equipment already. I had just returned my fins, so I ran to the equipment room to get them back real quick, ran to the jetty, jumped into a zodiac which was just about to leave, and got to spend some time snorkeling with the spinner dolphins. There were ten adults and two babies. Dolphins are fascinating animals: they are very curious, communicate using high-pitch tones, and sometimes perform acrobatic tricks.

You can also visit the hyperbaric chamber on your last day. The Baro Medical facility, run by the friendly Dr. Hossam Nasef, is just across the road. There your can see the hyperbaric chamber, which is used to treat divers suffering from decompression sickness. The chamber is still used around six times per year, but that number might rise due to COVID-19 therapies. It was built in 2005 and has a capacity of eight persons (six in the main chamber and two more in the airlock). The walls and doors are made of thick steel that can withstand the enormous forces of the air inside the chamber at 7.8 bar test pressure, 6 bar operating pressure. It has a small lock for passing medication, jet fighter-style masks for delivering oxygen, an intercom system, instrument panels that display equivalent depth in meters of seawater and temperature, three windows, air conditioning, a toilet and even an FM radio. Lighting and the camera system are rigged on the outside of the chamber to further reduce the risk of electrical fires. If a fire does break out in the chamber, pressurized water will be injected into the chamber through a spray nozzle. The room next to the hyperbaric chamber contains the pre-pressurized cylinders of air, water and oxygen.

Right next to the Baro Medical facility are the crew chalets, a small supermarket, the laundry room and the cylinder refill station. The refill chef gave us a tour of his operations. He refills around a thousand cylinders every day, just for Marsa Shagra. The large refill volume and close proximity to the ecolodge makes this economical. The refill station has multiple compressors for regular air, but the Nitrox refill system stood out. I expected the system to work with a regular air compressor and some way to mix in extra oxygen. Instead they first dry and compress the air to a low (10 bar) pressure, heat it up, pass it through a membrane to remove part of the nitrogen, and then use a high-pressure compressor to fill the 12L, 200 bar aluminum Nitrox cylinders. The benefit is that this method doesn't require a constant supply of expensive oxygen cylinders. It can produce up to 40% Nitrox within a 2% error margin.

On the way back to the ecolodge you can get a look at the owner's compound. It is a fenced-off area (complete with guard) and it contains the owner's house and those of his family members.

Airport shenanigans, part 2

My flight home was again delayed, but not by much. The one-hour delay was supposedly caused by some boarding pass system failure at Amsterdam Schiphol Airport. The check-in desks were still closing at the original time, so when I arrived at Marsa Alam International Airport a bit late, I was pulled to the front of the queue. It was not very busy at that time, the only other people in the queue were all flying to Frankfurt. Soon the small departure hall would fill up with mostly German tourists.

The airport has large TV screens that display a list of departing flights. Mine was still shown with the original departure time, without any remarks. I still had time so I set out for something to eat. There are only two food venues in the departure hall. A pizzeria that gave me food poisoning on my last flight in 2019 (NOT fun), and a small café. I went with the café. When I got my overpriced cheese-turkey sandwich, I opened it up to apply some ketchup and saw to my horror that its contents had expired. Green and white spots of mold covered the inside of the bread and parts of the turkey. I quickly returned the sandwich and got another one. Food safety is not much of a priority there. I spent most of the remaining time at the airport worrying about whether I would suffer another case of food poisoning, which luckily I didn't.

At some point I heard a woman's voice over the PA system announcing something about my flight. That was about all I could understand anyway, her English was that bad. Not seeing any updates on the screens I just assumed that she was re-announcing the delay.

Thirty minutes before departure I got the feeling that something was off. The plane had been on the apron for some time already. Surely they would have started boarding by now. There are only five gates at Marsa Alam International Airport. Two of them were in use: one for boarding passengers to Frankfurt, the other to Düsseldorf. Or at least, that is what the displays above the gates said. Still nothing on the departure information screens.

The airport does not have an information desk, so I just walked up to the guy standing in front of the Düsseldorf gate. He was shouting something unintelligible. I asked him where the gate to Amsterdam was, and he said "Amsterdam! Yes, this flight to Amsterdam". When I got to the bus that was taking me to the airplane, I met the other perplexed Dutch tourists.

Once at Hurghada we were instructed to leave the airplane so that it could be refueled. This was different from the flight a week earlier, where the pilot made the decision to refuel with passengers on board, probably because it was quicker and the airplane was already hours behind schedule. We were brought to the transfer waiting room. It was a sterile room, with hard metal benches, a bathroom and some windows through which you could see the runway and the customs booths. A bomb squad employee was quietly praying in the corner. Only passengers to Amsterdam were in this room, and we already went through security at Marsa Alam, but for some reason (and to much dissent of my fellow passengers) we had to go through the whole security theater again.

Back in the airplane the pilot announced that air traffic control in Cairo was understaffed. We had to wait some twenty-five minutes on the apron before we could depart. We arrived in Amsterdam at 02:15 in the morning, two hours and fifteen minutes after the planned arrival time. I am never able to really sleep in an airplane, so this flight was all but pleasant. Luckily my fellow passengers kept mostly quiet. Except for one moment where a woman in the row behind me was hitting her child and people were loudly protesting about it.

Schiphol was also suffering from personnel shortages at that time, and there were many piles of delayed suitcases in the hallways, but luckily our suitcases were on the conveyor belt in about twenty minutes. I took the night bus home and arrived there at around 03:30.

Download

dive shade
the place where people prepare for their next dive, 4.0 MB JPEG

view of the sea
as seen from the dive shade, 4.7 MB JPEG

restaurant and cafeteria
it's still quiet this early in the morning, 3.5 MB JPEG

reception and dive center
the dome on the reception building is relatively new, 4.0 MB JPEG

sightings board
a quick glance of all the buzz, 4.2 MB JPEG

jetty and zodiac boats
the captain's domain, 4.0 MB JPEG

main hyperbaric chamber
prepared for everything, 3.6 MB JPEG

two-person airlock
intercom and one of the oxygen masks visible, 4.4 MB JPEG

instrument panel
the instruments display pressure in meters of seawater, 3.9 MB JPEG

outside view of the chamber
medical lock, thick steel and external lighting system visible, 4.0 MB JPEG

pre-pressurized cylinders
from left to right: compressors, air cylinders, pressurized water system for extinguishing fires, and oxygen cylinders, 4.5 MB JPEG

panorama
from left to right: Baro Medical facility, Marsa Shagra village, the owner's compound, and a neighboring resort with jetty, 20 MB JPEG

Nitrox refill system
the high-pressure Nitrox compressor (light blue), 4.2 MB JPEG

nitrogen removal membrane
this tube removes nitrogen from the Nitrox refill air, 4.1 MB JPEG

regular air compressor
the refill station has multiple of these, 3.7 MB JPEG

service road to Marsa Shagra
mostly used by personnel, but it has a nice view of the ecolodge, 4.4 MB JPEG

Touch typing with GNU Typist

2022-04-10T00:00:00+02:00

One piece of software that I use all the time, both at work and at home, is the Vim text editor. I use it so much in fact that I recently decided that any investment in improving my Vim proficiency would pay itself off, so I asked my employer for a copy of the second edition of Practical Vim.

It is mentioned in the first pages that being able to touch type is imperative to learning Vim. Now I was already typing without looking at the keyboard, but I always typed the "wrong" way, with only my thumbs, index fingers and middle fingers. I could type with all ten if I forced myself, but it was slower. So now I am trying to improve that as well, alongside getting better at Vim.

For learning to touch type, I don't think there is anything better than GNU Typist. This simple ncurses-based program takes you from beginner to pro with the QWERTY, Dvorak and Colemak keyboard layouts. Its simple scripting interface makes it easy to modify lessons and create new ones. The built-in lessons are very useful and have helped me increase my touch-typing speed to around 50 words per minute. I can only recommend it.

Mobile air conditioning sucks

2021-06-12T00:00:00+02:00

With temperatures rising in the Netherlands and summer being just around the corner, most of us are looking for effective means to keep one's home or office (or home office) cool. The current heat record stands at 40,7 °C, measured on July 25th, 2019, near the city of Tilburg. There's no point in trying to get any work done in those temperatures. For me, the tipping point between "it's hot, but I'm coping" and "Jesus Christ who can work in this heat" is around 30 °C. That number might also be psychological.

Wind is also a huge factor. An example: the average high temperature while I was on a diving holiday in Egypt two years ago was around 40 °C, but this was okay as there was often a fresh breeze coming from the sea and I was in and around the water all day anyway. Then, one day I woke up and saw that the sea was completely flat. Not even a single ripple was to be seen. I walked into the restaurant where one of the Egyptian staff members was doing some live cooking. I asked him about the weather and he just responded, sweating excessively, "It's very hot today sir. Very hot."

To combat this heat, humanity has invented air conditioning. The ancient Egyptians already had passive air-conditioning techniques available to them, but nowadays the term 'air conditioning' is associated with A/C units that are powered by electricity. There are many types and sizes, but the thing they have in common is that they work by means of a heat pump and evaporative cooling. A compressor pumps the refrigirant, a substance that easily transitions between liquid and gaseous phases, between the evaporator coil and the condensing coil. The evaporative cooling takes place in the evaporator coil. Here, the refrigerant evaporates (transitions from liquid to gaseous), taking in a lot of heat. You'll want to have this side of the unit on the inside of the building. After this, the refrigerant passes the compressor where the pressure of the refrigirant is increased, allowing it to transition back to a liquid phase in the condensing coil, releasing a lot of heat in the process. This is the part that you want outside. The cycle repeats after an expansion valve which functions as a way to lower the refrigirant pressure before letting it pass through the evaporator coil again.

A type of air conditioning that is getting more popular is the mobile A/C. It is mobile in the sense that it has little wheels underneath and it can be installed somewhat temporarily. These units have a flexible hose that is used to transport hot air outside. There are, however, a number of issues with these units. First, the condensing coil, the part that is built to release energy in the form of heat, is inside the room. This part gets hot. In standard air condition units, the condensing coil is placed outside for precisely this reason. Second, there is the issue of transporting air outside. This lowers the air pressure in the room a tiny bit, causing it to suck air in from elsewhere, usually outside. On a sunny day this air is hot. Third, the air intake is in the same room, meaning that the mobile A/C unit basically takes in the air it just cooled, and throws it outside. And fourth, the exhaust hose is often long and badly insulated, causing it to lose heat to the same room you are trying to cool. It is also often hard to install the hose in such a way that outside air can't get in. I see many people just opening their windows in order to hang the hose outside. This vastly undermines the usefulness of powered air conditioning.

Mobile A/C units would be a lot more efficient if they had two hoses instead of one, so that outside air can be used to cool the condensing coil in a closed loop instead of sucking air in from outside. But alas, this would make mobile A/C units less attractive to consumers because you now have two bulky hoses to deal with.

If you are looking for some tips to keep it cool, here are my recommendations:

Try keeping sunlight outside before it enters the room. See if you can have awnings installed above your windows. If that is not possible, try light-coloured curtains that don't let light through, or stick special sunblocking foil on the inside (but preferably, outside) of your windows.
Open windows on both sides of the building in order to create a nice breeze. If that is not possible, open all windows and ventilation grates and put the mechanical ventilation system on max. Clean out your ventilation grates once a year.
If you notice heat travelling through your walls or ceiling, see if something can be done about the bad insulation of the building.
Keep it cool and drink a lot of water. Avoid consuming alcohol.
If you long for a constant breeze on your body, get yourself a fan.
If all else fails, have an air conditioning unit installed. Don't go with a mobile one.

A great video on the subject of mobile air conditioners is Portable Air Conditioners - Why you shouldn't like them from Technology Connections.

Running a Tor relay (Liberation Day special)

2020-05-05T00:00:00+02:00

Today is Liberation Day in the Netherlands. We celebrate the 75th anniversary of the end of Nazi occupation during World War II. A perfect day to write about freedom!

This article was supposed to go along with a meeting for (aspiring) relay operators in the Netherlands, but times being what they are, the meeting had to be cancelled. Thanks to the HVIV foundation for their intentions on making the meeting a success, and I hope that we can have our meeting soon. Let's try to move the discussion online for now!

Tor is a network of routers, so called 'relays', that anonymize Internet traffic through a process called onion routing. A technique originally developed by the U.S. Navy, onion routing takes Internet traffic through multiple relays before forwarding it to the final destination. Encryption aids in keeping the source and destination of the traffic secret. The sender encrypts the traffic with the keys of the intermediary relays, and each relay 'peels' off one layer of encryption, revealing where the resulting data should be sent next.

The Tor software (most notably the relay software and the Tor Browser) is developed by the Tor Project. Users of this software include ordinary people who value their privacy, but also activists, whistleblowers, abuse victims, stalker targets and dissidents of oppressive regimes. There are media organizations that rely on the anonymity provided by Tor for protecting their sources, as well as law enforcement organizations that use Tor for undercover operations and anonymous tip lines. And finally, militaries use Tor to protect field agents and support intelligence gathering. It was the military that pioneered on onion routing technologies after all.

Read more about Tor's history and design.

Now, onto relay operations. Let's see if I can answer your questions.

Should I run a relay?

If you are comfortable behind a computer, then yes, you should! The Tor network becomes faster, safer and more stable if you were to run a relay. Tor thrives on the diversity of its users and relay operators. The larger and more diverse the network, the harder it is to spy on any individual user.

What type of relay should I run?

There are three types of relays: guard, middle and exit. Their names refer to their positions in the network: the user connects to the guard relay, the guard connects to the middle relay, the middle connects to the exit relay, and the exit connects to the requested service (e.g. a website). As each relay forwards Tor traffic with their own IP address as the source of the traffic, it will appear to the requested service as if the exit relay is initiating the connection. You can imagine that this can cause trouble when someone is abusing the Tor network. It is therefore discouraged to run an exit relay unless you thoroughly understand the potential (technical and legal) consequences.

There is another option that you can try when you have limited bandwidth available, and that is running a Tor bridge. Bridges are essential to users in regimes where access to the Tor network is restricted. Access to Tor relays can easily be blocked because Tor traffic can be identified as such through network analysis, and because there is a public list of all Tor relays. There is no public list of all bridges on the other hand, and traffic between users and bridges is obfuscated to make it a lot harder to identify it as Tor traffic.

So back to your choice of relay: new exit relays are most appreciated because of their scarcity, but operating one should not be undertaken without fully understanding the risks involved. Next are guard/middle relays for when you have enough bandwidth available, and bridges when bandwidth is limited. Learn more about network, system and uptime requirements on Tor's relay operations website.

Where should I run my relay?

Whatever you do, DO NOT RUN AN EXIT RELAY FROM YOUR HOME. Doing so is highly discouraged as it will expose you to much higher risks of harassment and legal trouble. It will also make your own web browsing miserable because of all the "I'm not a robot" captchas and blocked pages. Running a bridge or a guard/middle relay from home is probably fine, but I felt the need to make it extra clear that it is not worth it to run an exit from your house. I've met people who, against all advise, still decided to run an exit from their apartment. They couldn't access their favourite tech website for months and got threatening calls from their Internet provider. And that's actually quite a good outcome considering the possibility of law enforcement kicking your door in for something that went through your exit relay.

You should run an exit relay with a dedicated IP address at a (professional) hosting facility with a competent abuse department. That last part may be hard to find out, but it's a good idea to contact the hosting provider and explain your intentions beforehand. It's a better option than having all of your services terminated for abuse of the terms of service and also contributes to a better understanding of Tor in the hosting world.

Guard and middle relays can usually be hosted anywhere given that doing so does not violate the law or any agreements with the hosting provider. However, if you have multiple hosting providers to pick from, choose one that doesn't host any relays already. Having lots and lots of relays at one hosting provider is not good for the diversity (and therefore security) of the Tor network.

How should I configure my relay?

This topic has been widely discussed before, hence I shall just point to the excellent documentation on the relay operations website. Try asking on the tor-relays mailing list if you need help. There are kind people on that list, including members of the Tor Project and yours truly :)

The Tor network benefits most from relays running on non-Linux systems (this is again because of diversity). Most relays run on Debian GNU/Linux. If you are comfortable running a relay on Windows, Mac OS, FreeBSD, OpenBSD or something more exotic, please do!

More (technical) considerations for running a relay can be found on Tor's relay operations website.

Additional considerations for exit relays

I run an exit relay (VrijHeid) together with another member of the Coloclue network association. Coloclue's abuse team consists of dedicated volunteers (who we are very thankful of). They receive abuse notifications from time to time which they forward to us. We ignore the notifications that look automated, but otherwise always send a kind and informative response. You can find our templates below (which were kindly provided by my former colleague, Bits of Freedom's Rejo Zenger). They may need some adjustments if you're outside of the Netherlands. In case of doubt, contact a lawyer.

As you can probably tell, proper abuse management is vital to running an exit relay. These were the steps that we took to reduce the burden on the abuse team:

Use a reduced exit policy to prevent most email and BitTorrent abuse.
Set the reverse DNS record (PTR) of the IP address to tor-exit.<domain>.
Host a webpage that explains Tor on the IP address of the exit relay.
Set up an email address that can be used to contact us directly and publish this address along with an informative notice in the relevant WHOIS database (see this RIPE database lookup).

Fully utilizing multiple CPU cores

If your relay hardware has multiple CPU cores, you should consider running one instance of the Tor software for every core. This ensures the best CPU utilization because Tor is single-threaded. The Tor network allows for up to two Tor instances per IP address. If you don't have enough IP addresses, you can try asking your hosting provider for more.

Your second (and third, fourth, and so on) Tor instance can run off of a copy of your 'torrc' configuration file. You will need to change some settings though:

DataDirectory must be unique.
SOCKSPort must be unique (or just disable it by setting it to 0).
ControlPort must be unique.
ORPort must be unique.
DirPort must be unique.
MyFamily must list the fingerprints of your other relay instances.
ContactInfo must be set on all relay instances.
It's convenient to make Nickname unique as well.

My relay runs on OpenBSD, where adding a second Tor service is quite simple. Just create a symlink like /etc/rc.d/tor2 that points to /etc/rc.d/tor, enable the service and modify the command flags with 'rcctl set tor2 flags -f /etc/tor/torrc2'. This ensures that the 'tor2' service is started with its own configuration file. You'll also need to add a 'tor2' section (the name must be the same as the service) to /etc/login.conf. Now you can start the second relay instance.

Conclusion

Go run a relay if you can! And if you can't, consider donating time or money to the Tor Project. COVID-19 has financially hit the Tor Project hard, too.

The mailing lists are a great way to get help and to contribute. Hope to see you on the tor-relays list, or at the next relay operators meeting!

Want to learn more about the history and festivities regarding Liberation Day in the Netherlands? Visit the website of the National Committee for 4 and 5 May.

Download

Abuse response template
OpenDocument Text, 16 kB

Law enforcement response template
OpenDocument Text, 12 kB

A book review

2019-12-05T00:00:00+01:00

I don't do book reviews usually, but I just could not pass on sharing this masterpiece with the rest of the world:

  The book is a guide book, a travel book.
  It is one of the most remarkable, certainly the most successful, books ever to come out of the great publishing corporations of Ursa Minor—more popular than Life Begins at Five Hundred and Fifty, better selling than The Big Bang Theory—A Personal View by Eccentrica Gallumbits (the triple-breasted whore of Eroticon Six) and more controversial then Oolon Colluphid's latest blockbusting title Everything You Never Wanted to Know About Sex but Have Been Forced to Find Out.
  (And in many of the more relaxed civilizations on the Outer Eastern Rim of the Galaxy, it has long supplanted the great Encyclopedia Galactica as the standard repository of all knowledge and wisdom, for though it has many omissions and contains much that is apocryphal, or at least wildly inaccurate, it scores over the older more pedestrian work in two important respects. First, it is slightly cheaper, and secondly it has the words DON'T PANIC printed in large friendly letters on its cover.)
  It is of course that invaluable companion for all those who want to see the marvels of the known Universe for less than thirty Altairian dollars a day—The Hitchhiker's Guide to the Galaxy.

From page 170 of The Ultimate Hitchhiker's Guide to the Galaxy by Douglas Adams, Proprietary Edition, 2017, in which this part of the novel The Restaurant at the End of the Universe (Adams, 1980) was republished.

Networking 101

2019-10-26T00:00:00+02:00

The third session of a computer networking workshop series was held yesterday evening at LAG Lab in Amsterdam. There were around ten attendees who listened to me talking about networking 101. I got some help from a guy who knew a lot about communications infrastructure in Britain. We lectured about these topics:

Physical infrastructure and Internet overview
The inner workings of a switch
Why routers are necessary
Digital vs. analog
Circuit vs. packet switching
Internet protocol suite
MAC and IP addressing
Frame and packet headers
Classfull vs. classless addressing
Counting in binary
Subnet masks and CIDR
Routing schemes

Yup, we covered a lot of ground in a mere 2,5 hours!

You can find the handouts in the download section of this article. The overview 'Map of the Internet' is editable in diagrams.net.

Interested in attending this workshop series? Make sure to follow radar.squat.net to find activities like this one at LAG. Next Friday promises to be fun as we will visit the landing site of the TAT-14 undersea fiber optic cable in Katwijk, South Holland.

Download

Map of the Internet
PNG with embedded draw.io XML, 119 kB

Networking 101
OpenDocument Text, 447 kB

PiBeacon

2019-01-11T00:00:00+01:00

Apparently you can use a Raspberry Pi 3 to make a Bluetooth Low Energy (BLE) iBeacon! Atif Omerovic and I wrote the script and documentation needed for this, and also created an Android app to detect the iBeacon signals. This project is part of the HBO-ICT IoT thematic semester at the Amsterdam University of Applied Sciences.

Take a look at the code repository here.

wifistatus

2019-01-06T00:00:00+01:00

I wrote some code for my college's thematic semester about the Internet of Things. The project consists of an ESP8266 board which continuously measures WiFi signal strength to a preconfigured access point, and a Django web server which processes and displays this information. Please don't use it for anything serious, it's not very secure. Just like most IoT devices...

Take a look at the code repository here.

Deploying DNSSEC at a web hosting company

2018-11-06T00:00:00+01:00

I wrote my System and Network Engineering bachelor's thesis about deploying DNSSEC at Byte, a Dutch web hosting company that primarily hosts Magento e-commerce websites.

Download

DNSSEC bij Byte
PDF, Dutch, 250.5 kB

DNSSEC bij Byte
HTML, Dutch, 150.6 kB

Imre Jonk

Tandem freefall

Download

internet linguistics

Scuba diving at Marsa Shagra

Table of contents

Airport shenanigans

Diving at Marsa Shagra

Accommodation and food

Things to do on the last day

Airport shenanigans, part 2

Download

Touch typing with GNU Typist

Mobile air conditioning sucks

Running a Tor relay (Liberation Day special)

Should I run a relay?

What type of relay should I run?

Where should I run my relay?

How should I configure my relay?

Additional considerations for exit relays

Fully utilizing multiple CPU cores

Conclusion

Download

A book review

Networking 101

Download

PiBeacon

wifistatus

Deploying DNSSEC at a web hosting company

Download