Interview: Dirk Hohndel


Dirk Hohndel


Interviewer: Many of us have used Subsurface for dive computer analysis or planning—myself included. So I was particularly delighted to exchange e-mails with the maintainer of Subsurface, Dirk Hohndel (Twitter). Besides making this incredible tool available to us, Dirk is also a pleasure to interview: not only does he have lots of great stories, but he brings us special insight into the community of open source divers. Thank you, Dirk, for taking the time for this interview.

Dirk Dirk showing off his trim. Nice!

Interviewer: by the way, the “Linus” fellow in this article refers to Linus Torvalds, whom we recently interviewed.

“If the sea could dream…”

Interviewer: Let’s set the mood with a story about a great dive. Something that gives us a glimpse of you in action.

The seemingly easy questions are usually the hard ones. Because… what do you pick? A crazy exciting dive? A dive that was incredibly beautiful and serene? Or, as an avid photographer, a dive where you got to take great pictures? I’ll pick one that might surprise you.

This is on Bonaire in October 2014. Linus and I came back from the morning boat dives, and as we dealt with our gear on the pier, Linus overheard two divers who had just done a shore dive talk about an octopus that was out and about right there—by the pier. It had been just over 30 minutes since our last dive. But heck, it’s super shallow, so we quickly got fresh tanks, analyzed them, geared up and went in. And then proceeded to spend two hours hanging out with an octopus, watching it hunt, watching a bar jack hunt together with it and generally just having the most amazing dive. I took some pictures and some video, but that really wasn’t what made it so memorable. It was watching that octopus. We never went below 4m, we didn’t move more than 20m from our entry point. The bottom there is basically “sandy rubble”. So nothing about this says that it should be amazing—but it still is vividly in my memory as one of my best dives ever.

Interviewer: Dirk sent both the dive profile, courtesy of Subsurface, and his octopus friend.

Dirk's great dive profile Dirk's Octopus

Interviewer: There’s always a point where one breathes from a tank underwater for the first time. When was that for you?

In the fall of 2010, Linus and I ended up going to a conference in Brazil together for a number of reasons, and he was able to add a side-trip to Fernando de Noronha in order to get some diving in. My plan had been to simply go snorkeling and relax while he was out diving (this was during my Sabbatical and the idea of a few days of doing absolutely nothing did sound promising). My wife had encouraged me to go (this was right after we returned from a family trip, so I had been a bit unsure) and also suggested that I should try SCUBA diving. I wasn’t convinced.

After Linus' first day of diving over dinner he talked about the amazing visibility and how much he loved the diving there… and somehow I ended up doing a “discover SCUBA” dive the next day after all. Linus actually joined me on that dive, but I had a Brazilian dive guide holding on to me through the whole dive. And oh my, it was amazing. We took a dive boat to a site that was actually very close to shore, and exactly at the same spot I had been snorkeling at the day before. Side note, I get really, really, and I mean really, sea sick. But thankfully that day the weather was super calm and the boat dive didn’t bother me. And of course I was distracted by the briefing. It was a beautiful site with huge boulders under water, lots of reef fish, amazing visibility—certainly a very unusual spot to take your first dive. A half hour dive, maybe down to 10 or 12 meters.

And of course I was hooked. 

After the trip, back in Portland, I signed up to get Open Water certified. After talking to some instructors I decided to do my open water “locally” (about 200km North of Portland, actually, at Hood Canal). This is where we start talking about the part of diving that I have mixed feelings about. I interviewed dive instructors to find one I was comfortable with. I picked a very experienced instructor, only to then get a bait and switch and end up with a different instructor that I didn’t really care for. And who did (both as perceived when it happened, and with the benefit of hindsight) a horrible job.

During my Open Water certification dives I went hypothermic (taking six hours in a warm/hot/warm shower to get feeling back into my feet on the first day) and on the second day went into a full panic on a decent, nearly losing my mask and almost aborting the whole thing, without my idiot instructor ever noticing. The only reason that this didn’t end my time as a diver before it ever really started was that Linus and I had already booked a trip to Hawaii that was literally going to leave two days later. I wasn’t going to cancel that.

And thankfully, that brought back the fun of diving for me.

Interviewer: Most folks take an open water course and leave it at that.  Was there a defined transitional moment when you felt yourself move into more serious territory when you identified diving as more than just passing entertainment?

After that horrid Open Water experience we went on two trips in rapid succession. I got certified in December of 2010, we went to Maui right afterwards, and to the Great Barrier Reef in January 2011. That was a short three-day liveaboard and as part of that trip I got my AOW. Once again with what I can only describe as a rather bad instructor—this time not in a “wow, this was dangerous” sense but much more because he didn’t care one bit - the students gave him money, he gave them the cert cards, regardless of what they did on the dives.

To understand how that ended up driving that “transitional moment” that you ask about, I need to mention that in between those two trips (because, reasons) Linus and I also went back to Hoodsport to take a dry suit (Linus) and dry suit/nitrox (myself) class with a different dive shop that I had found through pure coincidence after my Open Water excursion to Hoodsport. And that was a totally different experience. Two extremely competent instructors, a challenging, intense, and stimulating training environment. Great conversations with very experienced divers and the realization that while terrible instructors appear to be common, there are actually many great divers and quite a few great instructors out there.

Interviewer: naming names…

Hoodsport ‘n Dive—if you are in the Pacific Northwest and are looking for great dive instruction.

Dirk and Linus Dirk and Linus at Hoodsport 'n Dive.

So after coming back from Australia, and after realizing (sorry my friend) that Linus really wasn’t a great diver, we jointly decided, err, ok, I talked Linus into taking a few more classes. And over the next eight months we kept going back to the excellent instructor in Hoodsport adding more and more certifications, all the way to Divemaster and our first tech training. To me this was all about becoming proficient (and safe) as a diver. And having a dive buddy that I was very comfortable with and whom I could rely on blindly. I think Linus will tell you that he mostly went along because I set it all up and it was an excuse to go diving. But in the end I think he’d also agree that he now is a much better diver.

So within just about a year after my first discover SCUBA dive I ended up with 90 dives and a wallet full of cert cards. And thinking that I was an ok diver, more importantly a safe diver and that my dive buddy and I had gotten to know each other well enough as divers that we could be there for each other under water if it ever became necessary.

Interviewer: Linus complimented you in saying that you dive “like he’s on rails”, which I would consider a hefty compliment.  Did you find yourself naturally inclined to this, or was it something that came with a particular type of training—or just practice?

For some reason I always found buoyancy really easy and natural. During my open water training I took to it without ever getting any specific instruction. And on that first dive trip to Hawaii a couple days after getting certified the dive guide mentioned to me that if I hadn’t told him these were my first dives, ever, he would never  have thought that I was a complete beginner, based on how comfortably I was floating in the water. So there’s no particular trick or training. Just luck that somehow this seems to make instinctive sense to me. And of course, being interested in photography it’s something I do pay attention to when I’m in the water. But honestly, that came later.

And since I am being honest, of course then there are the moments where everything goes to hell in a hand basket. I will never forget my first dive with tech gear and twins on my back. And my buoyancy was completely shot which frustrated me so much that my air consumption was nearly three times what it normally is—which lead to the reasonable comment that taking twice the amount of gas on a dive doesn’t seem worth it when your consumption goes up three-fold in return. But thankfully after a couple of dives I got the hang of twins on my back (and even a couple of stage bottles) as well.

Underwater photography

Interviewer: Linus mentions you’re into photography, which is great, because it means I’ll have less work to do in hunting down photos to include. Did you have photography experience prior to getting in the water?

I’ve been an avid photographer all my life. As a kid I had my first SLR when I was 13. As I got older this slowed down a bit, but suddenly photography really became a hobby again when around the same time (a) digital cameras became better (or affordable cameras became better I should say) and (b) I became a father. My Adobe Lightroom database contains around 83 thousand pictures, only 10 thousand of which are underwater photography. I guess I do have a lot of pictures of my twin daughters…

Interviewer: Tell us a little about the progression of your photography—for example, assuming you didn’t start that way, at what point did you end up shooting RAW, manual mode, strobes and video lights, etc.

I started shooting RAW long before I started underwater photography. I know I played with this prior to the first Lightroom beta in 2006—but I think my experience with the early access LR versions really made me a true RAW addict. So I was going to say I always shot in RAW underwater, especially since my first underwater camera was a Canon S90 which was one of the first point and shoot cameras to support RAW. But then I went back and realized that the first 350 or so pictures were in fact JPEGs. And I have no idea why. According to Lightroom, in Nov 2011 I switched to shooting RAW under water as well. As I mentioned, my first camera was an S90. I bought a cheap (and crappy) Ikelite housing for it and initially had no external strobes. I took some surprisingly nice pictures with that setup, like this feather star fish (interviewer: below) in Okinawa, Japan, but the majority of the pictures were meh.

Again, going through my archives I can see that I added two Sea & Sea YS-D1 strobes and a tray to that setup in the fall of 2012. Which really helped to improve the average quality of my pictures. Like this one (interviewer: below) from November 2012 at La Herradura in Spain. No way to take a picture of the octopus in that amazing orange coral without strobes. Or this nudi (interviewer: also below) which was taken in February of 2013 on Lord Howe Island, Australia.

Incidentally, that was the last trip with my Canon S90. Soon after coming back home I ordered an Olympus OM-D E-M5 with the 12-50mm macro zoom, the NA-M5 Nauticam housing and a macro port for the lens. Switching from the point and shoot S90 with its focus issues and shutter delay to a mirrorless was at least as big a quantum leap for me as adding strobes had been half a year earlier. There was of course a learning curve. And things don’t get magically better just because you have a better camera. But I do think that overall my pictures improved. And that lens is simply perfect for the photographer who doesn’t want to have to switch lenses and ports. It takes great macro pictures (and a couple of years ago my wife got me a CNC-1 wet lens for super-macro), but also does really well for larger subjects. It’s not great for broader seascapes, but even now, five and a half years later, I can’t find a single other lens, regardless of system, that matches this lens. You get to shoot macro, then suddenly see something cool and take a wide angle shot. Like this this squid from a trip to West Palm Beach, Florida, USA.

Dirk and Linus Dirk and Linus Dirk and Linus Dirk and Linus

As for shooting manual vs program modes and manual strobes vs. TTL—I keep going back and forth and switching depending on the situation. I typically like having my camera on manual with the strobes on TTL, but for some macro shots I go all manual. And for other situations, especially when swimming around a reef at a site I don’t know much about, I may end up in program mode for the camera and TTL for the strobes. Doesn’t happen often, but it happens.

Interviewer: How do you rig your camera gear?

I have two short and two long arms with standard balls and floats on them—the strobes connect to those. A Sola focus light is connected to a very short ball adapter on my cold shoe. This shows the setup that I was diving with until last week.

Dirk Dirk Hohndel hiding behind an Olympus OM-D E-M5.

Regarding how I deal with the gear when getting in and out of the water, I have one short clip on the left side that I use to attach the gear really close to me when getting into the water or walking in on a shore dive. And a second coil lanyard that stays attached through the dive so whatever happens I can’t somehow drop and lose the gear during a dive.

Interviewer: Tell us about some challenging UW photography you’ve done; and then, when we’re impressed (I certainly am!), about some beautiful photography.

How about I give you two stories. They both happen to be from Bonaire. First, let’s talk about macro photography. Which is usually where it gets challenging. Getting that blenny to stick its head out, getting a good picture, in focus, with the eyes looking at you. I have spent many hours hanging by a small rock, waiting for the perfect shot. Linus is an amazingly patient buddy and tolerates these dives where we stay in one spot for ridiculously long times… and then you get this perfect shot. Looking at you, mouth open, in focus. Yeah, that was worth it.

And the other aspect of “challenging” typically is finding the animal you are trying to take a picture of. So let’s talk about sea horses. I love sea horses. Generally they are hard to find. And once you find them, they typically are in a weird spot where you can’t get to them, can’t get a good angle, can’t get light to them, or they look away from you. And then, every once in a while, you just get lucky.

Dirk and Linus Dirk and Linus

Interviewer: I see you have displaying some photos. Have you ever entered into photography contests you’d like to boast of?

Nope. I don’t think I’m even remotely close to good enough to do that. There are a lot of photographers out there who are leaps and bounds better than I am, and I’m ok with that. I enjoy the experience. The process of getting there. And I don’t want the competitive side of it take that fun away for me.

Interviewer: from my amateur perspective, Dirk’s photography is leaps and bounds above my own. Very motivating!

Tools of the trade

Interviewer: What was your first dive computer?  Follow-up, maybe the same: what was the first gear purchase you made that financially marked a transition from “hobby” to “expensive hobby”?

My first dive computer was a Suunto Gekko, a hand-me-down from Linus who had purchased his first air integrated dive computer at that point. The first expensive purchase that seemed to indicate that I might get a little more serious about diving was my own dry suit. Over the past almost eight years of diving most of these costs have amortized themselves quite nicely. Even the photography equipment, when broken down as “cost per dive” hasn’t been too bad. Of course, as I write this, I just this week broke down and after five and a half years of using my wonderful Olympus OMD E-M5 I upgraded to an OMD E-M1 MkII.

Interviewer: Inversion: have you ever lost any particularly valuable or meaningful gear?

You like reminding people of painful stories in their lives, right? The most embarrassing story of this kind is likely when another diver in our group misread the labels on the weights on a boat and went in under-weighted. And towards the end of the dive started being positively buoyant. I misread what was going wrong and thought she had problems with task over loading and tried to make things easier for her and offered to take her camera off of her. And then somehow managed to drop it and lose it. See my comment above about having that coil lanyard. Those two things are related.

And of course I’ve lost my fair share of other gear over time. The most valuable thing of mine that I lost was a Sola focus light. At the very end of a dive in Cozumel with pretty strong current it apparently shook loose. I remember that it was on my camera as I folded things up before the safety stop. But when I handed the camera to the boat captain I noticed that it was gone. Darn.

Subsurface and open source

Interviewer: Subsurface is a considerable piece of work.  Can you tell us a bit about your background in technology (pre-2012) that enabled you to handle the project?

I have been a developer since the mid 80s. I started with a ViC-20, switched to a C-64, an Atari ST and then finally a PC with DOS and more importantly Minix. At that point (1991) I “ran into” Linus on Usenet and very quickly upgraded my PC to a 386sx and started working on Linux around November 91. After that I got involved in porting the X Window System to Linux (or, more realistically, adding the features to Linux that were needed to run X) and became an active contributor, then Core Team member, and finally maintainer of XFree86. I worked on quite a few other open source projects over the years. By 2012 I had about 30 years experience in programming and more than 15 years experience in leading and maintaining large, distributed open source projects.

Interviewer: At what point did you start to get involved in Subsurface?  Did you know about the project from the inception, or before it?  Was there some direct interaction with Linus, or was it something you happened upon?

I actually had to go back through my email archives to remind myself. Linus did the first commit for Subsurface on Sunday August 28, 2011. We had just come back from our dive master training and from our trip to Vancouver, B.C. for the “20 years of Linux” celebration. We had talked quite a bit about the idea of creating a dive log and being able to download dives from a dive computer directly under Linux instead of running a Windows app in a VM (which I was doing at that point). He had played with the available software that did run on Linux at that point and absolutely hated the options. So he started his own. On September 1st he sent me an email with this awesome screenshot.

Dirk and Linus Early screenshot of Subsurface. How far it’s come!

The email may have mentioned that he thought he wasn’t great a writing UIs. I’ll leave you to judge that… my first commit to Subsurface apparently was a couple of days later on the 5th - which means that while I wasn’t the first external contributor, I did start contributing pretty much within the first week of its existence. So yeah, I knew about this before it became reality and started playing with it as soon as there was something to play with.

Interviewer: At what point did Linus force^Wask you to become the maintainer of the software?  Was it expected, unexpected?

Just like with git (which he maintained only for about six months), Linus didn’t want to maintain Subsurface long-term. He has this other open source project that apparently sucks up a lot of his time and that seems enough for him. He and I talked about me maintaining Subsurface pretty much since the beginning of 2012, but it looks like i didn’t take over as maintainer until September of 2012. I’m looking back through the email exchanges but can’t quite figure out why it took so long. I know there were many in person conversations on dive trips, so some context may be missing. I can’t see any particular milestone or anything else that we might have been waiting for. I had already done a lot of work on Subsurface at that point, including the Windows and Mac ports. And I started doing the releases even before I became the maintainer.

Interviewer: Decompression algorithms. Have you found yourself in challenging situations regarding the licensing (if any?), copyright, or IP of any deco algorithms?

No I have not. We have based our implementations on code that allowed reuse and on available documentation that allowed implementation of the algorithms described. I’m not aware of anyone claiming exclusive IP rights for the Bühlmann algorithm or for VPM-B. There are a couple of other algorithms that do appear to be IP encumbered and therefore we haven’t even looked at them.

Interviewer: More on these decompression algorithms. Was it your push to get this into the system?  Who was primarily responsible for the implementations?

Linus and I were taking our first tech classes when we discussed the idea of using the deco algorithm that the Subsurface developer team had started to implement for dive planning as well. I seem to remember that the first really crude attempts to make this work came from me, but pretty soon others took over and made the planner usable. We are very lucky to have an actual physicist in charge of this part of the code these days—he has optimized not only the implementation of the algorithms, but is also maintaining the UI these days.

Interviewer: The git history shows your first commits to create the planner in January, 2013. Were you “eating your own dog food” to plan deco dives of your own? (Was that scary?)

Ha. Whenever I intentionally do a deco dive (instead of just ending up in deco because I hung around some photography subject to long) I do of course plan it. And since Subsurface supported dive planning, I have used that for this purpose. But since I typically have two or three (or more) dive computers with me on a dive, I never actually dive the plan, but instead dive what the dive computers tell me to do (typically doing the most conservative superset of what they tell me to do, so that all of them stay happy).

Example dive planning An example deco plan with 30% twinset and 50% deco stage.

But lets be very clear here. I am not a tech diver. I am certified, I have done a handful of tech dives, I occasionally end up in deco on recreational dives, but nothing that I do should be considered by anyone as sane or something they should imitate.

Interviewer: Are there thoughts on edging dive planning into subsurface-mobile?

Subsurface and especially Subsurface-mobile suffer from having not enough UI developers. And the main work that would have to be done is to hook up a QML UI for Subsurface-mobile with the existing dive planning backend. A few people have said in the past that they’d be interested in working on this, but no one has submitted or shown any code, yet. So the honest answer is “maybe, I don’t know”.

Interviewer: a great project idea for divers who love open source!

Interviewer: have you seen developer interest in putting the deco planning itself into a tidy library? I know of a few open (non-C) libraries out there in wanting to write my own, but none that are tested and known.

Oh yes, we have been told by people that we “have to do that”. Because apparently that’s our purpose in life, changing our software so that other people can get what they want. Personally, I have no interest in this, and so far none of the other developers have shown any interest. The code is of course out there and available under the GPL. If anyone would like to work on it (in a way that respects the library—which means no, you cannot link this into your proprietary software), then sure, go ahead. But don’t wait for us to do it for you.

Interviewer: that sounds like an excellent idea for those of us interested in decompression algorithm implementations!

Interviewer: Subsurface challenges.  You brought the system from C into Qt/C++, integrated planning, cloud integration, the mobile version… the list goes on.  Which of these aspects was the most technically challenging?  Then which, in a non-technical sense?

Oh my. “most challenging”-style questions remind me of my children asking me “Papa, what’s your favorite vegetable?”… well, honey, there are a lot of vegetables that I like… Or to answer your question… there are a lot of technical challenges. Many are caused by the desire to have one code base for Windows, Mac, Linux, Android and iOS. Some are caused by packaging issues for the different OSs. Especially packaging for Linux is generally extremely challenging - because there are so many versions and flavors and variations. And then… I’m not a C++ programmer. I am a C programmer who stumbles around C++ code. So I often end up asking others on the team to help me figure out what some of the code in pull requests actually does and if that’s the right way to do things.

On the non-technical front… I think what I struggle with the most are rude and aggressive and demanding users. We create this project as a hobby, for free, across many different devices, with free cloud service, free support… you’d assume that the users are nice about it. And almost all are. But at least once a week I get an email or a post or an app store review where I end up asking myself “Why do I do this? Why do I spend all this time and effort and money to make this available to users, only to get treated like this?” So to me that really is the biggest challenge. But on the flip side, I love working on the code, I love working with the amazing developer and translator community that we have around Subsurface, and I love hearing from all the thousands of users that do appreciate the work. And that’s what I keep reminding myself… it’s less than a percent of the users who are the ones that are just pissing me off. And so I ignore them, block them, and move on.

Interviewer: Another question that deserves some time: libdivecomputer. Can you tell us a bit why subsurface has a locally-maintained branch?  Do you anticipate being able to resolve the differences with Jef (Jef Driesen) to keep things separate in the future?

Let’s start with a clear statement. If it wasn’t for Jef and libdivecomputer, Subsurface as you know it wouldn’t exist. It’s that simple. He has done an incredible job over the years to support all of these dive computers and to maintain this library.

With that out of the way, there are areas where Linus and I on the Subsurface side and Jef on the libdivecomputer side disagree. Let’s call those philosophical disagreements. I am sure he finds us as frustrating as we, at times, find him. And as a result we ended up adding features to our branch of libdivecomputers that he didn’t want to have in his version.

Interestingly, for one of the bigger ones (the custom I/O layer) he then years later turned around and implemented something very similar himself. But frustratingly he implemented his own thing. Different enough to make it painful for us to switch. And (as far as we can tell) there wasn’t really a good reason for why he ended up doing that. We threw away our code, spent the time and effort to port Subsurface to his new implementation and ended up temporarily breaking things for a few users because some of the different design choices that he made (all that should be fixed by now). Frustrating? You bet. A huge issue? Nah, life goes on. There are other features that we have in our branch that his version is lacking. I’m still hoping that at some point he’ll come around to seeing their value. Because I’d much rather not maintain our own branch. But until that time, we’ll just continue doing it this way. This is one of the huge benefits of all of this being open source. We have the option to do our own version.

Interviewer: a user of libdivecomputer myself, I’m also incredibly grateful to Jef for his work. He’s arguably the most central figure of the entire open source ecosystem. Thank you again, Jef, for your excellent work!

Wrapping up…

Interviewer: Have you ever tried free diving?  Not in the “professional” sense of competitive breath holding, but simply as an alternative to space-suit diving.

No I haven’t. It just doesn’t seem all that interesting to me. I mean, especially as a photographer, the ability to spend long time in one spot in order to get the perfect shot… that’s a big part of what makes all this interesting.

Interviewer: The future of Dirk and diving: what’s next on your plate?  An exciting location?  CCR, if not done already? Do you find yourself enjoying the diving/photography skills you have, or is there something you’d like to improve?

CCR won’t happen. I don’t like dealing with devices where the default failure mode is “YOU DIE”. Sadly two friends of mine have already died during CCR dives—one of them was a Subsurface developer. I have absolutely zero interest in that. Less than zero. And as the previous question may have indicated, the 50m free dive also doesn’t hold any appeal for me, either. Also, I love traveling to interesting destinations, but I also love going back to places I have been and that I know that I enjoy. Palau, Bonaire, Fiji… yeah, I’ll go there again. In summary—I guess I am boring…

So to me what’s next is really taking better pictures. There are some areas where I think I do ok, and there are many others where I look at pictures from other photographers and realize that I’m a complete beginner and have a ton to learn. Which mean there is room for growth, room for enjoyment, reasons to go diving. And that, in the end, is what makes this all so enjoyable. Go on a dive trip with some friends. Spend time in the water, spend time with Lightroom, enjoy the process. All this is about enjoying what I do.

And I do.

Interviewer: The last questions I have are a bit more general. The first is rather canned and regards the future of subsurface in general. Do you have a plan (har, har) for its mid-term future, or is development mostly in response to need?

Neither, actually.

Almost all development is based on supply, i.e. based on what the developers who are contributing to it are interested in and find the time to work on. There are of course conversations along the lines of “hey, it would be nice if we could implement XYZ”. But unless someone then actually goes and does it, that’s really not any indication of where things will go. As a matter of fact, there are a number of things that really should be done, and that several developers have shown interest in, but that haven’t happened. That’s how things go in truly volunteer driven open source projects.

Interviewer: Wrapping up… open source and diving. We have libdivecomputer and Subsurface, open photo and video editing, and of course our operating systems of choice. Do you see any open components as missing from the toolchain? Similarly, do you see the open source diving ecosystem at risk from any current or upcoming technologies or business forces?

We have outstanding open source dive computer. The Heinrichs Weikamp OSTC series is proof that you can create open source based products in this space. And Matthias Heinrichs is a wonderful supporter of Subsurface.

Interviewer: Jef also spoke highly of Matthias and his OSTC work.

But I think most divers don’t think in these terms. Linus and I certainly dive with decidedly not open source dive computers. More than 90% of the users of Subsurface are on Windows, Mac, Android, and iOS—all of which aren’t open source (some people pretend that Android is, but let’s be serious here). I have used a Mac as my main computer for almost a decade and a half. Sure, I have Linux in a VM on there, but that doesn’t mean that I don’t use macOS (and use Subsurface on macOS) all the time.

I am a huge fan of open source software and have spent more than half of my life working on and investing in open source software. That doesn’t mean that I’m unwilling to use proprietary software when I believe that it better suits my needs. This isn’t an ideology for me. This is all about what works.

Interviewer: at this point, I asked Dirk if there were any questions that he would ask himself. So we switched roles for a question or two…

Interviewer: You have a day job, you work on Subsurface, you dive, you are an avid photographer. Does that leave time for anything else?

I am a husband and father and try to spend plenty of time with my wife and kids. And as part of that, I have been training Taekwondo with my whole family for the past nearly decade. I currently hold a third degree black belt and am working on becoming a “Master” (4th Dan). Taekwondo is an amazing sport that is in so many ways the exact opposite of diving. It’s about strength, explosiveness, and technique—which to me makes it the perfect counterbalance to diving.

Interviewer: Subsurface is complex software—many divers might want to help with the development, but this does not look like a project where a beginner might feel welcome. How can people contribute who aren’t rock star developers?

Many of the developers aren’t rock stars. Quite a few of us aren’t developers (any more) in their day jobs. That includes me (I’m an executive in a very large software company). But there are so many other ways to contribute to a project like Subsurface. Obviously through testing and reporting bugs, but equally importantly by helping us with translations, documentation, our web presence—and many other ways to make the software easier to approach for other divers. So if you are interested in helping, reach out to us and we’ll be happy to figure out what you can contribute. Simply send me an email at

Interviewer: Many thanks to Dirk for taking part in this interview. To contribute to Subsurface, start by just using the software! It’s source repository is Subsurface-divelog/subsurface. I look forward to what Subsurface has coming; and Dirk, if you’re ever in our fair Malta, then be sure to drop a line so we can take you to our favourite spots!