Donut Blue Hole, near Andros Island, Bahamas
July 30, 1999

This is a short description of a short trimix cave dive in a Bahamas Blue Hole called Donut Blue Hole. This cave is just offshore of Andros Island, a 40 minute boat ride from New Providence. Boat and mixes were provided by DiveDiveDive. Diving the cave was Paul Christman and Joel Markwell. Paul was to enter the cave as a solo diver; Joel and I were a buddy team.

The depth of the cave was unknown to us, but was guessed to be in the 360fsw range. Due to logistical problems, Joel and I decided the entire dive, including deco, should last only about 70 minutes. All depth/mix/deco calculations were adjusted for that outcome. A lot of flexibility was also calculated in. Our target depth was 210fsw, but we had enough room in the mix and deco process to bounce to 240fsw if we wanted. Paul's mix would allow him to go much deeper, down to 320fsw.

The entry was from a roll off the boat. I was taking my video camera, so I got all set before I started breathing my gas. Nitrox 50 -- for deco after the dive -- was carried as a stage, and was to be dropped at any convenient ledge. Pure O2 was hung from the 20-foot down line below the boat. Water temp was 85-degrees F, and the cave water was not expected to be much cooler.

I knew I had more Nitrox 50 than I could ever use, so I started breathing it on the drop into the blue hole. At 50-fsw, I switched to my 17/35 back gas.

The blue hole has a flat, sandy area in the middle, at about 40 fsw, surrounded by a circular depression, as if some giant had pressed a donut into the coral, leaving a giant impression of a donut. On one side of this hole was a large crack, about 15-feet wide, about 40-feet long, which opened into a much larger cavern.

While not a cavern dive, light from the sun could be seen from most parts of this cave, especially if you stayed by the line.

We tied off the primary reel at about 120-feet and dropped almost straight down. At about 190-feet, we could see the permanent line, and we tied off. The permanent line and the walls were covered with a white, slimy bacteria culture. It was so thick that our bubbles dislodged it wherever they hit it, and the result was very similar to ceiling/silt percolation. My video showed little else but these globules of bacteria. There was virtually no life at all in the cave, so I imagine that the bacteria used up all the oxygen in the water (that's just a guess). Excluding the bacteria, there seemed to be only a little silt on the horizontal surfaces.

The cave was not "tidal"... there seemed to be no flow at all.

The permanent line angled down just slightly below the horizontal, starting at the 190-foot tie off and ending at about 200' feet of penetration and 210-fsw depth; at that point, the line took a sharp turn straight down. Paul had preceded us into the cave and was already about 50feet below us and was continuing down.

I swam around the cave, staying near a wall since, without it, my video camera would have nothing to focus on. The room was quite large, maybe 80 feet by 40 feet, and huge limestone boulders sat wedged in gargantuan cracks. After swimming about 50 feet away from the line, I looked down and could see Paul ascending. I swam back to the line and dropped down a bit, following Joel into the abyss. We both stopped our descent at about 235fsw.

I had brought along a Scuba Pro sonar depth gauge and pointed it straight down. The reading showed "30 feet". I couldn't see 30 feet down -- the bubbles from Paul and the bacteria globules were making it tough -- but I felt sure it was deeper than that. Later, Paul confirmed that the hole bottomed out at 265fsw, so the depth finder was correct.

Our "turn" was upon us, so we slowly ascended and retrieved the reel at 190fsw. We stopped at 120fsw for our first deep stop. We retrieved our Nitrox 50 bottles and started breathing them at 60 feet. The remainder of the deco stops were uneventful. While we were at the 20-foot stop, hanging like limp dolls on the line, several black-tipped reef sharks came over to investigate, but we weren't on their menu for lunch.

Dive time including deco was 72 minutes.

Although there wasn't much to see except the bacteria, it was a fascinating dive!

(Photos to follow later.)