Deep Cave Dive at Song Hong, Thailand


There’s a certain feeling that arises when tying into the end of a deep cave line.  As you are laying new line in virgin cave, there’s this unmistakable burst of adrenaline being injected into your system. You can feel your heartbeat, your synapses sharpen and you can clearly hear every sound, click and hiss the rebreather makes.

This time is no different.

Mike Gadd had a double scooter failure in Song Hong around the 135m mark as the pressure had made the o-rings squeeze the propeller axe to a halt.

I decide to scooter to 120m to save time, drop the scooter, then swim to the last tie off.
It takes me only 8 minutes to arrive at the end of the line at 153m, the same one Pekka and myself laid a good half year ago.

The video showed a drop into a black void. I tie off into the last arrow and start laying out line. The viz isn’t that good, around 20meters as opposed to the 40m in the shallower parts and the drop isn’t that steep. Instead I’m facing a lunar landscape of rocks strewn around on a perfectly polished beach.

I negotiate my way between the rocks whilst tying off every 10m.

After another 8 minutes, the bottom seems to go up again and I decide I’m far enough for now. My double twenty litre stage tanks allow for a 20 minute swim back to the 90m mark. I also carry two 300 bar carbon tanks on my butt d-ring. As they are positively buoyant, they carry a bit of the weight of all the equipment. I make a final tie off at 177M just above a small hole. I cut the line, place an arrow and start swimming back. With one hand freed, I can now turn on my 11000Lumenvideo light to look at the bottom. In the bottom of the landscape I see multiple black holes which are just too small to swim through. The question is, where are these holes going? Is there another passage below this level?


Then in the corner of my eye I see something crawl away. 5m further I see something else and I move closer. A white-pink millipede-like worm crawls over the sandy bottom. It’s about 2 inches long. Yes, it is just a worm, but, in 6 years of diving in song hong, I have never seen any living creature below 25m. Thermoclines and different dissolved gasses make it basically impossible for any creature to sustain life below these levels, except for some bacteria clusters feeding off hydrogen sulphide and Co2…. yet, at these depths, there is this worm having its own empire.

I make my way back past the 150m mark and face a dilemma; both my computers show completely different decompression stops/profiles. My plan correlates most with my old computer, but I don’t want to ‘bend’ my other computer, so I start doing the deep stops. First stop is at 126m… 15 minutes later, I’m still crawling with 3m increments and only just past the 100m mark. My other computer has now added another hour of deco; 6 hours to go. Not good. I won’t be home in time for dinner, so I decide to fall back on my old trusted computer and my plan. 5 minutes later the first computer tells me I’m dead, whereas I see a little smiley face on the older one.

Miscommunication with the support crew means that my back up air supply is not at the 50m mark as discussed. The briefing was too hastily done and I curse myself for not having written it down.


I had a light trimix in my drysuit to keep me a little cool during all the finning at the bottom, but I’m now cooling down rapidly. The air tank also had my isotonic drinking bag on it and I start to get cramp in my right foot. This is mainly because of loss of fluids and salts, but also because of the vasoconstrictive effect high oxygen exposure has on your extremities, limiting blood flow.

As I arrive too late at the rendezvous point, I just catch a glimpse of the safety diver, who quickly signals an ok sign with his torch and disappears. He has been waiting at the 50m mark longer than anticipated because of the extra deco my computer gave.
Finally, at the 20m marker I get my air and my fluids. I feel warm and hydrated within 15 minutes and back on the happy track.

Ben R Photo 3

Once at the 12m area, I can offload most tanks on the custom platforms that are cable suspended at 12 and 9m with a habitat/bell at 8m of depth.

After 4 hours I finally reach the habitat. Cameron helps me to get out of my rebreather and into the habitat, where I start breathing pure oxygen. The air in the habitat is being ‘cleaned’ with a custom scrubber and a computer fan powered by a motorbike battery.

I’m out of the water waist up, my pee valve is below the surface and a big catfish keeps me company on the seat next to me, attracted to what comes out of the pee valve. Multivitamins and electrolytes tend to colour urine fluorescent yellow and I wonder if that is it what attracts the catfish. He remains unfazed as I’m being served hot lasagna… I forgot to put a spoon in the bag and try to scoop the lasagne with the lid of the box. Next time Cameron surfaces inside the habitat he pictures a massacre as my face is covered with lasagne and he nearly chokes in his regulator.

After another 2 hours I crawl back into my rebreather and slowly surface. I get a mild pain in my knees when surfacing, something I had as well on the 239m dive after 3 hours in the habitat. I guess my knees should keep moving during deco instead of sitting down to promote the helium getting out of my joints. The pain goes away quickly; I crawl into the truck and fall asleep.

Ben R Main article photo and thumbnail

Max depth; 177
Runtime: 366minutes
Number of gasses carried: 7

At this moment, the shape of the main tunnel remains a mystery. Earlier dives revealed another drop below the ‘slope’ that characterises both sides of the tunnel. If so, then the tunnel would have the shape of a ‘keyhole’, with a much deeper bottom. The width measured on a scooter (very inaccurate) is roughly 200m, where the height is approx. 100m. Rather vast.

Ben Reymenants

Ben Reymenants

Ben Reymenants’ passion for diving began in 1982 with inspiration from the classic James Bond movie, ‘For Your Eyes Only’, where divers salvage a computer hidden in a shipwreck. He has been diving in Fiji, Bonaire, Egypt, Tenerife, Thailand, France, Sri Lanka, Australia, Indonesia and Scotland. Having begun his dive training with CMAS, Ben is now a Technical Diving Instructor Trainer for PADI, SSI, TDI and IART for all levels (his highest level is IT for CCR Cave Level IV). He can teach tech courses in 5 different languages. Ben and his partner Simone currently own and run Blue Label Diving in Phuket, Thailand. In addition to Phuket, Blue Label Diving has facilities in Bangkok, Brisbane (Australia), Bunaken and Lembeh (Indonesia). Blue Label Diving teach technical diver training from Sidemount to CCR Rebreather down to deep trimix and Cave Courses. For more information, visit

scroll to top