On May 15th, George K. Watson and Emanuela Bertoni conducted a dive in the Pit cave in Quintana Roo, MX. The purpose of the dive was to develop exploration possibilities, look at the existing work and note new leads along the existing line. We also were interested in extending our methods of diving as mixed open circuit/manual CCR team.

The planning for the dive began shortly after our last dive to the end of the Wakulla Room. We developed a far more aggressive plan requiring multiple support and staging dives and a much larger gas load for both divers. We planned the open circuit/bailout decompression gasses to give ourselves a wide range of average depth and bottom time possibilities as information regarding the cave configuration is limited at this time. We also planned for a series of training dives to refine techniques for dealing with contingencies as a mixed team in zero/low visibility and under other varied stressors.

The bottom gas plan consisted of using 15l/HP130 cylinders filled with 10/70 to 3500psi to be used for stage switches and in case of an emergency. Emanuela carried five stages filled with 10/70 and George carried three. She would have 400cf of usable gas added to the 260cf on her back for a total of 660cf of 10/70. George carried the same 260cf of back/bailout/diluent gas along with three stages of bailout gas. Each bailout gas stage carried a QC6 equipped regulator to allow George to drive the rebreather from a stage in the event of a total backgas/diluent loss. We planned to start utilizing decompression gasses at 190ft based on the best information we had about the cave. We placed two 80cf bottles of 21/35, four 80cf bottles of 35/25, four 80cf bottles of 50/25 and three bottles of 80cf O2 in the system. George carried an additional 80cf bottle of O2 for the drive gas for the rebreather and as a start on bailout decompression.

We planned on taking four scooters into the system, dropping the first two somewhere around twenty minutes into the dive, burning the second set for up to 40 minutes, then switching back to the originals.

The team exercises went well despite some small (real) failures and we felt ready to pull the trigger on setting up the system. The shallow support team placed the first bottles in the system three days before the dive and the deep support team placed the remaining bottles at 190ft and 240ft (safety bottles) the following day.

During the time we were training during the day, we were busy filling our cylinders at night with the huge amounts of gas that were going to be required. All of the 10/70 cylinders and the O2 cylinders had to be finished with a booster, which was very time consuming. The booster was unable to help with the large doubles, so we turned to Bernardo at Cuzel for a solution. Utilizing his own helium feed invention, he used the large compressor at Cuzel to pump our doubles with helium, finishing them with the 32% needed to make our 10/70. His help in this area was crucial to us.

We took a day off to relax and get focused and on Sunday we woke early to do final preparations. Lucio and his surface support crew met us at the junction of the trail and road and carried the scooters down. Adam Korytko and David Mayor delivered the stages, doubles and rebreather to the cenote. Lucio lowered all the equipment into the basin. We dressed and jumped in along with the support team. The support guys helped us into our gear, passing us breathable regulators as needed as our bottom gas was not usable on the surface.

At around 2pm, we began our descent after having dealt with a few small regulator issues. At 120ft Emanuela switched from her travel gas to the bottom gas. Given the planned depths and duration of the dive I decided to run the rebreather at 0.8/0.9ATA PPO2 and I quickly made my adjustments. We checked all the deco tanks on the way down, ensuring the integrity of our deco gasses. We took 6 minutes to make 120ft. After Emanuela’s switch, we got on the trigger on the first scooter set and headed in. We checked our remaining deco and safety bottles at 190 and 240 ft on the way to the first bypass. We passed the first T prior to the bypass restriction at 10 minutes, or four minutes of trigger time after the descent. We scootered the restriction and reached the second T, a four way intersection, about a minute later at the beginning of the Wakulla room. At 12 minutes Emanuela switched her first bottom stage, about the middle of the Wakulla room at about 290ft. We hit the third T at 14 minutes. at the end of the Wakulla room. At this point the line goes down sharply and to the left into an interesting set of low passages and a restriction and the deepest part of the dive. Emanuela dropped her second stage and we dropped our first scooter set just before the deep restriction at 16 minutes. The passage here descended significantly into a low bedding plane and then went up through a restriction. The low bedding plane is at 350ft, the deepest part of the dive. The rock here is incredibly soft and the percolation effects and just the passing of two divers quickly reduced the visibility to zero. We passed a T prior to entering the restriction at about 20 minutes where the line goes left and up and hit the restriction at 21 minutes at a depth of 340ft. We were incredibly careful in this section, moving slowly and deliberately pushing the remaining scooter in front to avoid any unnecessary silting, though the visibility was already zero from the percolation. We entered and quickly traversed Jill’s Chamber, entering a large tunnel.

After this, the cave opens tremendously into a beautiful tunnel with stark white ceilings and blue water. The surface of the ceiling looks lunar with small pock marks contrasting the white. This tunnel seems to go forever and is a mesmerizing. We did another stage drop at the start of the tunnel at 25 minutes. There was a parallel line on the right side and then an odd junction which forms sort of an ‘H’ between the two lines that we hit at about 30 minutes. Past the ‘H’ we jumped to the right hand line as the left hand one had ended. Not long after this we did our fourth stage drop at 38 minutes. Shortly after this we arrived at the end of the SMB line and began following the line recently installed by the Polish team. We followed the line for a while until we turned the dive on gas at 54 minutes. There was a ‘Y’ junction with a white arrow where we turned the dive with the right line with heading slightly up and the left line continuing at the same depth. Riding back together we were both struck by the beauty and the possibilities in this tremendous cave.

Passing back through the restriction and the percolation was uneventful. Back in the Wakulla room we traversed efficiently to the bypass restriction, scootering it again and heading for the safety bottles at 240 which would mark the beginning of the deep stops for our decompression.

We had spent 90 minutes at an average depth of 290-300, so we would have significant decompression to do. Using the UTD cascading ratio deco method, we determined that our time on O2 would be 140 minutes, with an additional 140 minutes spent on 50/25. We would do 70 minutes on 35/25 and 35 minutes over the seven stops from 190-120.

The support team joined us at 120ft removing our surplus bottles/scooters. We were pleased to be relieved of our extra burden as we would have to manage our deco bottles for a while. We finished the 190ft-130ft segment and 120ft-80ft segments uneventfully and arrived at our 70ft bottles where the support team had left a Camelback with a mixture of electrolytes and water. At 60ft, a little more than 5 hours into the dive, my scrubber started to break through and I switched to open circuit, spending the rest of the 70-30ft segment and the entire O2 segment on open circuit. This was expected, given the length of the dive and there was plenty of planned bailout deco gas available. The little over two hours of the O2 segment was spent relaxing, eating, drinking and writing notes about the dive. At one point after dark we switched off our lights and just relaxed in the darkness. The support team visited us a couple of more times in this area, checking how we were doing and watching our gas supplies.

At exactly 8 hours, we started a 20 minute ascent moving slowly up the line to the surface. We were met by our support team who stripped our gear and got everything sent up to the edge of the pit. After stripping our suits and rinsing ourselves off, we relaxed at the site and drank some more water and a little coffee. There were no issues with the decompression and we enjoyed a relaxing evening.

We feel we have reached the limit of what can be done practically and safely with open circuit technology and have validated our methods of diving as a mixed team. Being the 2nd and 3rd persons to have a look at this area of the system was a tremendous honor and something we will never forget.