Out of Africa

By J. Grogan & S. Murray

Lying at the southern tip of the Kalahari Desert in South Africa (approximately 100 kilometers south of Botswana and a little further from Namibia) is a game farm called Mount Carmel. This farm sits on a plain, randomly dotted by a few small hills, near the road from Kuruman to Danielskuil. From the farmhouse, about a 30-minute drive through herds of impala, kudu, springbok, buffalo, the occasional ostrich and many other creatures of the veld, takes one to a large sinkhole at the edge of a plain. Framing the sinkhole lies a sea of flat land.

Here lies the famous Boesmans Gat cave. Resting at the intersection of two fault lines in the northern Cape Province, the cave’s genesis is hinted to by the fault lines; one wall is a fairly straight wall lying along a fault line. Over time, the water level has dropped and one can only marvel at what might once have been. The water level is now about 80 meters (265 feet) below the top of the sinkhole and occupies a tiny corner of the overall area. The descent down to the water is quite arduous, and requires steady balance and a firm resolve. In this environment, a group consisting of Simon Murray, Cronje Grove, Andrew Collins, Kevin Munroe, Don Shirley and John Grogan decided to spend up to one week exploring the cave.

The system is famous due to its size and depth. It can best be described as a massive chamber (at its widest it is approximately 1.2 kilometres (4,000 feet) in circumference) with an ice-cream cone at a top corner that leads to a restriction through which one enters the cave. At its deepest it is 286 meters (944 feet) at an altitude of about 1,500 meters (5,000 feet)...

For years, divers in South Africa had been diving Boesmans Gat and attempting depth records. It achieved international prominence in 1993 when Sheck Exley joined with local diver Nuno Gomez to explore the cave. Sheck’s line can still be found in the cave. During a depth record attempt in the early 1990s, two ropes were put in place leading from the surface to the deepest part of the cave. These ropes are marked off at 3-meter (10 foot) intervals with loops for attaching bottles. Due to a subsequent drop in the water level, the depth markers are no longer accurate. Sheck’s line runs from one of these ropes right across the chamber to tie into an outcrop at 64 meters (212 ft) on the other side.

Gomez later conducted a record-breaking dive to the bottom (286 meters (944 feet)) where he reported the existence of a layer of silt about 1.5 meters (4 feet) thick. The main chamber opens up rapidly down to about 80 meters (265 feet) depth after which it appears to be fairly constant, although there are a number of ledges that start at 90 meters (295 feet) that have yet to be explored. The cave may indeed continue to open up in sections. Deep divers have reported that below 150 meters (495 feet) they have been unable to see any of the walls of the chamber; however, this may just be a result of poor lighting.

It took the best part of five hours to get our equipment down to the water’s edge. This consisted of two Halcyon semi-closed rebreathers, with twin 15 Liter (95 cubic foot) bottles mounted on each side, two Gavin scooters, many stage bottles, doubles, a stretcher, oxygen equipment (the nearest chamber was seven hours away), a first aid kit and the other usual DIR equipment. The altitude got the better of one of the authors of this essay, who for two days found himself rather surprised at being winded from the work. For the project, we also took with us a number of J bottles of helium and oxygen, a compressor and a Haskel pump, but these were left at the farmhouse.

We prepared for our first dive. The entrance pool quickly leads to a small crack (approximately 1.5 meters (5 feet) by 3 meters (10 feet)) through which one had to drop. On our first dive, we were using nitrox and decided to swim. This was primarily to get used to the cave and to get a feel for its layout. We also wanted to explore down to 30 meters (100 feet), which is like the shaft of an ice-cream cone. At about 35 - 40 meters (115 –132 feet), the cave really begins to open up. This was unlike any cave John Grogan had experienced in France, the UK or Florida – the floor was about 250 meters (825 feet) beneath him! We had a look around the cave in this depth range but found no leads.

That evening, we discussed the dive further and the objective of the coming week. It was believed that there were a number of passages leading off the main chamber, at depths of up to 100 meters (330 feet), which fed it with groundwater. Our objective was to explore the cave down to a maximum depth of 100 meters, locate any passages, and where possible, explore some of them.

A few months earlier, Simon Murray and Greg Maud had done some exploration in the 55-65 meter (182 – 215 foot) range, but without rebreathers or scooters. This time we decided to continue exploring in that range the next day, but with the proper equipment! The water clarity was amazing; with visibility stretching as far as one’s light could penetrate. However, most of the walls were covered in brown mud that absorbed our light, the effect of which was to reduce the perceived visibility. Our plan was to first use the main ropes as our reference point down to our chosen depth, then tie into a rock at the side and lay line along the wall.

After a good night’s sleep, we drove to the site and prepared for our dive. On this dive we took stages of 50/25, 35/25 and bottom...

gas, as well as a scooter, through the narrow crack. The depth of the line varies depending on the availability of suitable tie-offs and the path of the ceiling. We found the line and followed it clock-wise around the room. We reached a tie-off where the line headed straight down; realising, however, that the final tie-off had come undone, we cut the old line. Here, John tied in his reel, hit the trigger and kept going until he reached Sheck´s line. Sheck´s line starts at the ropes (at about 40 meters (132 feet)) and goes across the chamber to the opposite end where it is tied off at about 66 meters (218 feet). Having reached our agreed bottom time, John tied into Sheck´s line and stowed his reel. We turned around and started looking again at the walls in the 50 - 75 meter (165 – 248 foot) range, searching for leads, but could find nothing.

We started our ascent and decompression, and ended up with an in-water time of 130 minutes. The maximum depth we reached was 72 meters (238 feet), our average depth 62 meters (205 feet). As we reached each subsequent gas change stop, we clipped off our used bottle and took a new one. On subsequent dives, we would pick up these decompression bottles and deposit them back at their MOD stops. On each dive, we took out our bottom stages and our 50/25 bottles. As these deco gases were being used through the rebreathers, we never used more than 5 - 10 bar (74 – 147 psi) of gas. As a result, there was never a need to extract these bottles for refill.

Our plan was to use one stage of bottom gas for each dive, as well as the required stages of decompression gases. This meant that our back-gas was not to be touched unless there was an emergency and we had to go to back-gas on open circuit. Typically, it took 15 to 20 minutes on a scooter to return to the main ropes on top of the ascent to our first gas change; in the event of an emergency, 30 Liters of open circuit provided ample gas for this. As a result, in the evenings, we could use the Haskel to pump gas from one stage to the other and then fill one stage with bottom gas.

The next day we scootered clockwise and reached Sheck´s line where John had tied off the previous day. Here John tied in once more, hit the trigger, and eventually reached the other end of Greg and Simon's line (on a subsequent dive, they had travelled counter-clockwise laying line). John now tied into this, and we went back over the section we just covered, into the northeastern alcove, to look for leads. We explored the walls in the 50-75 meter (165 – 248 foot) range but again found nothing. So, we turned back and returned to the ropes where we commenced our ascent, having done a 45-minute bottom time. Having satisfied ourselves that there were no passages in the 50-75 meter (165 – 248 foot) range in the room, we decided to mix for 80 - 90 meters (264 – 297 feet) the next day.

A previous sonar survey indicated a ledge that began at 80 meters (264 feet). Under the ledge, the cave really opened out; so we decided to have a look in there. As usual, we put in line around the walls and searched for passages. We dropped down the main lines, and at a depth of 85 meters (280 feet), John tied off onto the wall. We then started in a clock-wise direction, dropping under the ledge to examine the wall beneath for evidence of a passage. Progress was relatively slow as we continually stopped to tie off the line.

We kept going until we ran out of line and tied off to the wall (we were using Extreme Exposure’s 1,200 foot reel). We were at a depth of 86 meters (284 feet). We turned around then and scootered back to the ropes. When we reached the ropes, we had had a bottom time of just over 30 minutes, so we decided to exit.

When John got back to the surface, he had a rasping cough, indicating that he had fried his lungs on decompression. Though John had been taking gas breaks to back gas before each gas switch, as well as "air-breaks" at 6 meters (20 feet), it was obviously not enough time off. A modification would need to be made to subsequent decompression schedules.

Our plan the next day was to scooter to our previous tie-off, and continue the circuit; taking time to explore the northeast alcove. This area between 80 meters (264 feet) and 90 meters (297 feet) looked the most promising from the sonar survey, and we wanted to take a good look at it. After dropping down to 85 meters (280 feet), we found the previous day’s line and started scootering along it. When we reached the previous day’s tie-off, John tied in, and we hit the trigger. We had decided that we would just complete the circuit today no matter how long it took.

Approaching the alcove, we spotted a large crack in the wall, which we initially thought would lead to a passage, but close inspection revealed nothing of interest. We continued on, scootering slowly around the alcove, examining the walls, but found nothing. We turned into the final stretch, but then unfortunately ran out of line. John guessed that we were only 90 – 120 meters (300 - 400 feet) shy of completing the circuit, but we were not going to use our emergency spools to plug the gap. John tied off and, looking at Simon, could see that he was also disappointed. The scooter ride back took about 20 minutes during which we put in some line arrows as we went. We thought from the sonar surveys that the circumference was less than it turned out to be, hence the reason why we ran out of line.

As we made our way back, we both began planning tomorrow’s dive, thinking that we would complete the circuit before dropping down to 100 -110 meters (330 – 363 feet) to have a look. We reached the vertical ropes, stowed the scooters, and started our ascent with our first stops starting at 69 meters (228 feet). Our total in-water time was just over three hours.

That day, a cold front started to move in over the country. Temperatures dropped to freezing overnight and about 4 degrees during the day. That night, during the braai (colloquial term for BBQ), we had a big bonfire to keep warm. Snow was recorded in Natal province, and many drivers on the main road from Johannesburg to Durban were stranded in snowdrifts. This was not looking good. That night we went to bed unsure of what the morning would bring.

The worsening weather convinced us not to dive. After getting a weather forecast, we decided to call the diving, and instead pull out all the equipment. It took us about 5 hours to get it all out, and, despite the cold temperatures, found ourselves to be pretty warm as a result of this. We stripped everything down, cleaned the rebreathers, packed everything up, and prepared for an overnight drive back to Johannesburg. It continued to get colder, with strong winds adding to our misery. Our hands went blue, and almost useless as we struggled to pack everything. After eating, we grabbed a few hours sleep before getting up at midnight to drive home.

Epilogue

The trip to Boesmans Gat came about after talking to Simon Murray earlier in the year about diving in South Africa. Simon had done some dives there with Greg Maud the previous year and was eager to return. After discussing the project further, we decided that a combination of Halcyon rebreathers and Gavin scooters was the next step forward. John’s unit was in Florida at the time, but there was a spare unit in South Africa that he was able to borrow (thanks to Mike Beresford for this). John shipped his scooter and other equipment out the week prior to the diving. The equipment choices of Halcyon semi-closed rebreathers and Gavin scooters were perfect for an isolated cave site that was both big and deep, requiring complex gas logistics.

Expedition Logistics

Boesmans Gat is in a very remote part of South Africa. As a result of this, significant logistical planning was required. With us, we took a number of J bottles of helium and oxygen, a Haskel pump, as well as stretchers, first aid kits and oxygen kits. Use of Halcyon semi-closed rebreathers in this environment provided a significant advantage when it came to gas requirements and planning. This resulted in having to fill only one stage each evening. Thanks to Don Shirley for organizing the gas and Haskel as well as doing all the fills.

Decompression Requirements

In our dive planning, we decided on a maximum narcotic depth of 20 meters (66 feet). This resulted in the use of 15/50 Trimix for dives up to 60 meters (220 feet) and 10/70 Trimix for dives up to 90 meters (297 feet). We fed the rebreathers from AL80 stage bottles, leaving our back gas intact in case of emergencies. We also used AL80 stages for all deco gases.

For the decompression, we used 35/25 Trimix (from 36 meters (120 feet)) and 50/25 (from 21 meters (70 feet)) Trimix, as well as oxygen from 6 meters (20 feet). All decompressions were planned using both GUE’s Decoplanner and VPM-based models. Bottom times varied from 30 to 40 minutes, with in-water times of over three hours. We used dry suits with DUI C4 undergarments in water temperatures of about 19? C (68? F).

An example of our decompression for the last dive (90 meters for 35 minutes) is:

Note that stops prior to gas switches were done on back gas to allow our lungs to recover from elevated ppO2s. Oxygen stops were conducted on the basis of 15 minutes on oxygen, 5 minutes on back gas (without stopping the decompression clock). The ascent to the surface was done on 50/25 Trimix after having spent about 5 minutes on back gas before leaving 6 meters (20 feet); the ascent took about 6 minutes. On the surface we spent about 10 minutes marveling at the dive before exiting the water and de-kitting.

 

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