Interview speakers Duikvaker 2025
Impossible expeditions as a challenge

Text: René Lipmann Photos: Vic Verlinden
Pim van der Horst likes to dive on wrecks that hardly anyone has been to. These are usually wrecks that are either very deep or in a location that is not so easy to get to. He dived with rebreathers early on, at a time when these systems were very
got a bad reputation. When he attempted a record deepest wreck dive to 232 meters, there was even a bet on his life.
You started diving at the student diving association Falco of the University of Tilburg. We are talking about the eighties. What was your trigger to start diving?
As a boy I was a fan of the Thunderbird 4, from the TV series Thunderbirds made in the sixties. Thunderbird 4 is the favorite vehicle of International Rescue for underwater rescue operations: a yellow mini-submarine, piloted by aquanaut Gordon Tracy. I thought it would be fantastic to explore the underwater world myself. As a student I was given that opportunity. All you needed was a sports card. You then had lessons and could borrow diving equipment. That was done in the NOB way: swimming pool training every week, a central swimming pool exam in the KNMA swimming pool in Breda, a national written theory exam and a national open water exam. More than a year of hard learning and training. All that for your first star, comparable to the open water certificate.

You started your own diving school and saw the benefits of diving with nitrox early on. At a time when nitrox was called Voodoo gas. How do you look back on that time?
I was very fascinated by technology. Whether it was equipment or, for example, the gases used in diving. I was curious. I also wanted to try out new things. In the diving world, people were already talking about nitrox. Not only as a Voodoo gas, or a gas of which you did not know exactly what it was and what it could do to your body. People also often talked about the explosion hazard of nitrox, due to the high oxygen content. Many organizations, such as PADI and the NOB even banned nitrox for this reason! To obtain my Nitrox certificate, I could only go to the Dutch department of an American training organization: ANDI. In the beginning, it was almost impossible to fill nitrox anywhere. So I decided to do it myself.
During this period rebreathers were also introduced. Not much later you dived with an Inspiration eCCR. What is a rebreather?
A rebreather is a diving device that ensures that you do not blow the exhaled oxygen into the water, but reuse it. Hence the name rebreather, which loosely translated means re-inhaler. On the surface you breathe in air. Air consists of 21% oxygen and 79% nitrogen. You only use the oxygen to generate energy in your body. You breathe out the nitrogen. But you do not use all the oxygen: you breathe out 16%. You can reuse that 16%. The shortage of oxygen, after all you need at least 21%, is then replenished. This can be done by a computer or you can do it yourself. There is a disadvantage: the process of generating energy ensures that the used oxygen is converted into a waste gas: namely CO2 (carbon dioxide). That is poisonous to humans when inhaled. Because you want to reuse all the oxygen, the system must be closed, because otherwise you would lose the oxygen that you exhale. But in a closed system, the CO2 also remains. You have to filter that out. For that, you use a chemical substance that takes care of that. That chemical substance can become very unpleasant when it comes into contact with water… So there are some disadvantages to a rebreather. However, fortunately, the number of advantages is greater.

You were certainly not welcomed with open arms on board a dive charter with a rebreather. That was not a reason for you to hang up the rebreather?
Rebreathers had a bad start. There were quite a few fatal accidents in the beginning. Also in the Netherlands. That gave rebreathers a very bad reputation. It took years before that came to an end. In my opinion, the cause of those accidents was not the fault of the device, but the ignorance of the diver. A rebreather is simply a more complex device than regular diving equipment, or open circuit. As knowledge about the device increased and training on the device improved, the number of accidents decreased very quickly. In all honesty, it must be said that the number of accidents on rebreathers is still higher than on open circuit. In my opinion, that is because many rebreather divers seek out the extremes: such as very deep dives and very long cave dives. With rebreathers, much more was suddenly possible. As one of the first rebreather divers in the Netherlands and one of the first instructors, I was dismissed as a murderer and someone who was tired of life. The Inspiration rebreather was even yellow box of death mentioned. When I went to do my record attempt deepest wreck dive to 232 meters depth, there was even a bet on my life. The people and organizations that shouted that so loudly, now all dive with rebreathers themselves. Dive charters now prefer rebreather divers over open circuit divers on board, because they can take more divers with them. They therefore need to take much less helium and oxygen on board: rebreather divers use much less gas.

So what are the major advantages?
Diving with a rebreather has more advantages than it seems at first glance. The most important is perhaps the gas consumption. You need far fewer gases to make (deep) dives. With the current prices of helium, this also saves a lot of euros. The bottom times you can make are much longer and your decompression stops are often shorter. The logistics are also a lot easier: you need to take far fewer gases with you. And that applies even more on board a charter or when you dive in remote locations without diving facilities. You also stay warmer on a rebreather. The filtering process of the CO2 ensures that the gas in the rebreather becomes warm. You then breathe in nice warm gas. As a cold-water diver, you benefit from this. When you dive with a rebreather, you do not make bubbles. This has the advantage that you do not chase away fish and that you cause less sediment in caves. Handy for photographers!
Are there any disadvantages to a rebreather?
Rebreathers also have disadvantages. For example, they require more maintenance and longer preparation for a dive. Training also takes longer. You have to dive in a different way, because your buoyancy changes and you have to learn to handle the device. Training not only costs more time, but also more money. A rebreather itself also costs around €10,000. In addition, you also have to regularly replace the oxygen cells and after three hours of diving also the CO2 filter. You can save yourself a lot of money on the cost of helium.

You fully embraced rebreather diving and specialized in technical diving. You also started participating and organizing CCR expeditions. Tell us!
Most of the expeditions I have done would not have been possible without a rebreather. Huge investments in logistics would have been necessary. Think of gases and diving tanks. For example, there was an expedition to Bunaken in Indonesia. A so-called Coelacanth was spotted around a volcano in the sea. The animal was said to be the link between fish and humans. Until then, the Coelacanth had only been seen in South Africa. So we went looking. However, the animal can be found from a depth of 100 meters! National Geographic was a sponsor of the expedition. We had to provide helium and oxygen locally. That was only available in small quantities. If we had to do all the dives with open circuit, we would not have been able to get enough helium and oxygen. By the way, we did not find the Coelacanth…
Another expedition was that to the Britannic?
That's right! That's the sister ship of the unsinkable Titanic of the shipping company White Star. I've dived on it twice, a total of eight dives. A third expedition is planned for 2025. White Star built a total of three Titanics: the Olympic, the Britannic and the Titanic. The Titanic sank in 1912 after hitting an iceberg. Of the approximately 2,224 passengers and crew, only 705 people survived. The Britannic was transformed into a hospital ship during the First World War. The Britannic sank in 1916 after hitting a mine during the First World War off the coast of Athens. She now lies there at a depth of 120 meters. Of the 1,066 people on board, 1,036 people survived. One notable survivor was Violet Jessop, a stewardess who survived both the disasters of the Titanic and the Britannic. She was known as Miss Unsinkable. The Olympic, the older sister ship, had a much longer and safer life than her sister ships. She was involved in a few incidents, but never sank.

You can just dive on that?
Organizing such an expedition takes a lot of time and resources. The first time I was busy with it for almost three years. Especially getting permits to dive on it was a challenge. That required a lot of money. To ask people to help me and also to mobilize the lawyers and civil servants. During the dives themselves, a representative of the government was present on board. An ROV also had to come along to film our dives. This way it was checked that we did not break anything or steal parts. It is a bit easier now: the Britannic and a number of other wrecks have been designated as tourist attractions. You may visit these under strict conditions. It is also a problem in other countries: shipwrecks are often seen as sea graves and cultural heritage. These rules also apply to the Netherlands. I had a lot of problems diving on the wreck of the Karel Doorman near Indonesia in the Java Sea. I wanted to make video recordings there to record a piece of Dutch history. In the end I was forbidden to do so by the Dutch Navy: after all, it was a war grave. It is ironic to discover a few months later that the bell from the Karel Doorman was offered for sale on the internet by Australian divers. It is even more ironic to discover a few years later that the conclusion that the wreck had disappeared. Probably the Chinese stole the wreck and sold the iron. You understand that I find it an eternal shame that our expedition did not continue. The Netherlands is missing a piece of history because of this!
What is the purpose of a diving expedition for you?
My personal goal of such expeditions is to dive on locations with historical value: the wrecks. Especially wrecks that hardly anyone has been to. These are usually wrecks that are either very deep or in a location that is not so easy to get to. For example, I was one of the first divers on the Haven and the U455, both in Italy. Now those wrecks are on the list of every technical trimix diver.
You hold a world record, tell us more.
Yes! Through an Italian student of mine I was asked if I wanted to participate in a record attempt in May 2008 to the wreck of the Milano in Lago Majore. That wreck was a recently discovered one with a remote controlled underwater camera (ROV). The wreck lies at a depth of 240 meters. We were going to make the dive with three people. More divers were requested, but they did not want to participate. It was going to be a record in several areas: the deepest wreck dive ever made and the deepest team dive. And that on rebreathers. I hesitated between the Megalodon and the Ouroboros rebreather. It became the Ouroboros. More than 70 people worked on the preparation and execution of the dive. Standby divers, medical staff, gas blenders, people who built the diving platform, journalists and witnesses for the record attempt. We finally made the dive with a total runtime of eight and a half hours and a bottom time at 232 meters of three minutes. During the preparations we were on Italian TV every day. A Russian team of journalists made a documentary about it that you can watch on YouTube. The record is still unbroken.

Another notable expedition was not to a wreck, but to Boesmansgat. An extremely deep cave in the middle of South Africa. What attracts you to such a location?
Boesmansgat is certainly a very special destination. It is one of the deepest known caves in the world. Boesmansgat is also known for Dave Shaw's fatal dive. He wanted to retrieve the body of another diver, but died in the process. To date, one diver has reached the bottom: Nuno Gomez. The famous cave diver, who unfortunately also died during a deep dive, Sheck Exley has also dived there. The bottom is around three hundred meters. The cave itself is located in a reserve, among the wild animals, in the middle of South Africa. And difficult to reach. It is quite a logistical operation to get all your diving equipment, gases and compressors there. To reach the entrance of the cave, you also have to climb quite a bit. If something goes wrong, help is only available over a distance of hundreds of kilometers. There we reached a depth of 170 meters with three divers. The nice thing was that we were an international team again with divers from the Netherlands, England, South Africa and the United States.

Rebreathers are now commonplace in many locations and outnumber open circuit divers. What happened?
Rebreathers have become a familiar sight on charters, but also on the waterfront in Vinkeveen. The rebreathers themselves have become a lot better and therefore a lot more reliable. The training courses have also become more thorough and better tailored to the average diver. That makes a rebreather a lot more accessible. There are also many more suppliers and brands of rebreathers. There are also many more extreme dives. These are made easier with a rebreather. The bad reputation of rebreathers is starting to disappear. There are more people who can and want to afford a rebreather. In addition, technology does not stand still. There is a lot of work being done on technological developments to make a rebreather even more reliable and even easier to use. Think for example of CO2 sensors and solid state oxygen cells.
You will be giving a presentation at Duikvaker on February 1 and 2, what can I expect?
It will be an interactive session! Not a one-way presentation, but a conversation with a journalist in which the audience will also be involved. And there will certainly be an opportunity to ask questions. The conversation will be supported by spectacular images.

Pim van der Horst
Pim van der Horst is a passionate wreck diver and instructor with 40 years of diving experience. Over the years he has specialized in technical diving. He has participated in and helped organize several CCR expeditions. Pim is perhaps the only diver who has made dives deeper than 200 meters with several CCRs. During his career Pim has published several books on (technical) diving, including Rebreathers Diving Without Bells. Pim's Tekdiving PTD is an organization that focuses 100% on technical diving. You can follow courses from Nitrox diver to Tri-Mix Instructor Trainer.
www.tekdiving.nl
Share this message: