Text by Brock Brinkerhoff
Photography by Curt Bowen
Photo: Descending into the blue hole abyss, explorer Brock Brinkerhoff hovers at a depth of 250 feet and peers into the darkness below.
The azure seas of the Caribbean lie before us. We are aboard the Nekton Pilot, a unique live-aboard vessel designed specifically for diving. As we idle from Port Everglades, we see Fort Lauderdale in the distance.

This trip is special for the Nekton Pilot – it has been devised as a rebreather live-aboard, organized by James and Nikki Smith of Monkey Diver Travel. Of the thirty-two divers aboard, fully twenty-five are on closed circuit rebreathers. The trip will take us past Bimini, then south to an area north of Cuba known as Cay Sal Bank.

Cay Sal Bank is the third largest of the Bahamas banks, and is closer to Cuba than to the Bahamas proper. It is 50 kilometers (31 miles) from the north side of Cuba, and is part of the Bimini district of the Bahamas. It covers an area of 5,226 square kilometers (2,017 square miles).

We leave Fort Lauderdale near 11:00 p.m., and cruise through the night. The next morning, as we near Bimini, the Nekton crew dispatches their skiff. It is here that we have officially entered the Bahamas.

Taking stock of the rebreathers aboard, many of the manufacturers and models are represented. There are Optimas, Megalodons, rEvos, KISS Classics, Evolutions, and Inspirations. With this assortment of varied rebreathers come their unique owners – each person with a slightly different take on why they dive a rebreather, and what they hope to accomplish on the trip. One of the rebreather owners is John Chatterton. He is joined by his wife Carla, and this is a vacation for them. No work to do, no tasks to complete.

Most of our time aboard the Nekton Pilot would follow a typical schedule of breakfast in the early morning, followed by a dive site brief. From here, the dive deck would be open until lunch. During lunch, the boat would typically move to another site. Once we had arrived, the dive masters would conduct another dive site brief, and the pool would be opened until dinner. Once dinner was over, a dive brief would be followed by a night dive.

We spent the first few days diving on relatively shallow sites. This would allow us to shakedown our gear, and get any issues ironed out.
By day three, we had made our way south to Cay Sal Bank. This is what we'd come for – multiple dive sites featuring incredible blue holes, many whose extreme depths were previously unexplored. It was early morning as we arrived at our first site – the fittingly named Big Hole. This site is .5 kilometer (1/3 mile) in diameter, and had an unknown depth. The Nekton's depth sounder was only capable of 152 meters (500 feet), and wouldn't register a depth over certain areas of the hole. During the briefing, we heard about some interesting features of the hole, such as a large breakdown area that offered a swim-through as well as a handful of resident sharks.

As I splashed in and descended to the pin, two blacktip sharks immediately surrounded me. Although the smaller of the two didn't bother me, it was the two-meter (six foot) long version that I kept an attentive eye on. Academically knowing that these sharks are generally wary of people did little to dull my attention.

Once I was joined by my teammate, we moved to the hole – the edge delineated by blackness. Because of the sheer size of the hole, it appeared to be a 90-degree wall to nowhere. As I descended, the reef seemed to roll into the hole. Life was everywhere, from small reef fish and lobster, to larger tuna. Some of these animals seemed curious about their bubble-less intruders, and swam right to us.

As we descended further, the reef melted away to raw rock. We had reached a depth where light and the current could no longer provide for extensive life. Even here, we found lobsters taking advantage of the recesses that the walls afforded. Swimming along felt like being weightless in a great canyon. Although I couldn't see the other side, I knew it was there.

The wall itself was a constant reminder of the tremendous processes that created it. Some areas contained enormous breakdown piles, while others were sheer faces – not unlike those seen in the Grand Canyon.

As we started a slow ascent along the wall, we came upon the breakdown we had been told about. It appeared like a vertical pillar of rock that had collapsed and, coincidentally, landed across an area of erosion. This had the effect of creating a canted slab of a roof over two outcroppings. The sheltered area this created was 5 meters (15 feet) in diameter, and at such an angle as to have light cascade down through it.
During our lunch surface interval, we had talked with one of the Megalodon divers named Bobby. He had searched deeper along the same area we had descended into, and found that it continued sloping down. Although the vertical wall transitioned to sand, the sand itself gently sloped ever deeper.

Our second dive was at the same site, and we splashed in for a look at the wall-to-sand transition. There were many fossils in the sand, ranging from coral to other shelled animals. As we descended and the light dimmed, our HID's lit up the surroundings. It was strikingly similar to one of my local dives, a flooded limestone quarry – the walls and craggy rocks gave way to the sloping, sandy bottom. This continued into a wide black plane, where my HID couldn't penetrate more than 20 meters (60 feet). After swimming for a few minutes into the center, I turned and headed back to the wall. This hole would continue on, at least for me, to an unknown depth.
As we finished our diving for the day with a fantastic meal, a few of us went to the top deck to watch the night dive. There were some prototype lights on board, and these where being tested during the night dive. With the clear water and very little moon, the lights could be observed for the entire length of the dive in the hole. No matter the depth obtained, the hole glowed with an eerie glimmer.

As we left Big Hole for our next site that night, the captain mentioned that the sounder hit a spot on the far side of the hole where it didn't return a depth, indicating that the hole was deeper than 152 meters (500 feet). The deepest measured blue hole known to exist is Dean's Blue Hole. At 202 meters (663 feet), it is located in a bay on Long Island, Bahamas.

The next day we awoke to calmer seas and our new dive site: Sistine Chapel. This site was known for its coral heads surrounding the blue hole, along with many varieties of fish. The site got its name from the extreme undercut that existed at approximately 25 meters (80 feet). On descent, it had the odd effect of leaving you in space, as the ceiling retreated the wall, now some 6 meters (20 feet) away. Interesting formations of stalactites dripped from the ceiling, along with intertwined wire coral.

Dropping down the wall, it was curious to find more lobsters, sometimes whole pots of lobsters, hiding in the walls. Given the depths, I wondered how they moved about for food – they were a long way from any horizontal surface with the exception of the floor of the hole they hid in.

As we descended further into the hole, the walls blended from life to lifeless – color to colorless. There seemed a distinct line where creatures decided inexplicably, it would appear, to stop frequenting. It made me think of an inverted tree line in the mountains. Life and its selection process deemed this area too harsh except for the most robust creatures.

The walls here, too, were much like my local haunts – huge walls of rock and striations, layer upon layer of aged rock and sediment, crushed together over time. This hole also had the similar junction of the rock wall stopping at a sand incline, which drifted ever deeper and beyond the range of my HID.
Back on the Nekton Pilot, I conversed with Bobby again. He'd had a great dive and was sharing some of the same observations. He was excited about what he had seen as he had swum closer and deeper to the center of the hole.

As the day wound down, John approached me and asked whether I wanted to do a dive with him the next day. I jumped at the opportunity. Given his history in diving, I looked at it as a way to learn from a much wiser and more experienced diver.

We spent the remainder of our day planning our dive, setting up gases, and filling bailout cylinders. We also enlisted the help of some of our friends on board who would provide support for our dive. Once the plan was ironed out, we turned in early that night.
Moored to our new site, Silver Sides, our plan was to splash as close to 8:00 a.m. as possible. This meant getting up early, grabbing breakfast, and making the final preparations. We did a final pre-brief on the plan with the support divers, and readied our gear. We splashed just prior to 8:00 a.m.

The boat was positioned directly over a shelf, just off of the hole itself. As we splashed, we tied in a spool to the pin, and swam towards the edge of the hole. The entire reef at the edge was incredible. This was the most life we had seen on the trip. As we paid out line and dropped over the side, I couldn't help but admire all of sea life and the reef itself.

For this dive, the spool line was to act as a known descent and ascent reference. We would place a strobe on the line at an agreed upon depth – this would act as a beacon for our ascent. It would also act as a meeting place for our support divers. They would know exactly where to expect us.
Descending into this hole was different. The interface between decorated reef and lifelessness was much more dramatic, as was the chill of a thermocline – the water temperature dropped to 24C (76F) from the surface of 31C (88F).

Darkness set in quickly, and the lights came out. Me with my trusty 10W HID and John with a prototype LED light head. As we descended, the wall undulated from ledge to undercut. Descending even deeper, it was as though someone turned the “Scale” knob up – all of the features appeared rougher, less worn, and larger gaps appeared between eroded walls. The undercuts also became more severe. This resulted in a zigzag swimming pattern in order to stay in visual contact with the wall.

The darkness and cold grew stronger. The pair of us, staying in close proximity, kept moving our lights at elements of the wall. From huge ceilings of an undercut, to the fast approaching ledge we would need to swim out and over.
As we neared our agreed upon depth, we slowed to admire the wall and the next ledge below us. We knew we had reached our goal, and that our time here would be short. As we hovered in the darkness peering beyond the next ledge, all we could see was the blackness of a hole that went on. The mystery of the Cay Sal massive blue holes continues for yet another expedition.

Divers getting ready on the dive deck, Caysal Banks