The Green Banana is one of many sink holes that dot the gulf floor. In fact, if it were possible to drain the Gulf of Mexico, it would probably look like Swiss cheese with all the sinks scattered about. People rumored the Green Banana to be deep. Exactly how deep was unknown? Other divers had explored to a depth of about 320 fsw. Reports showed that it just kept going.

In 1993 an expedition to search for the bottom of the Green Banana. Curt Bowen, a veteran cave explorer originally trained by Sheck Exley, led the expedition. Other team members included Frank Richardson, David Miner, Jim Cutway, Capt. Larry Borden, and Win Remley. The team set out loaded with eight sets of doubles and 32 singles, filled with various mixtures of nitrox, trimix, air, and oxygen. The team planned several exploratory and two deep penetrations over four days.

The Green Banana Sink is in the Gulf of Mexico 42.3 miles west of Sarasota, Florida. Several stories exist that tell how the Green Banana got its name. The most credible seems to be that it was discovered by a fisherman (as most sinks in the Gulf are) who got an outstanding catch while trolling around the sink. As he was pulling in his lines, he noticed a case of green bananas floating by-hence the name Green Banana.

This trip to the Green Banana was planned after an exploratory survey dive the previous year by Curt Bowen. Not knowing the maximum depth of the sink, the team pre-calculated decompression tables for depths from 300fsw to 500fsw in 10 foot increments, each with a 15 minute bottom time. Both Dr. X and DPA decompression software were used to plan the dives and decompression schedules.

Two setup divers initially set up the site by anchoring two ascent lines to the Gulf floor at 154 feet next to the opening of the sink. Large orange surface floats held the ascent lines taut. This also minimized ascent line motion because of surface waves. The opening f the sink was measured to be 134 feet wide. We laid a guideline with direction markers across the mouth’s diameter, attaching it to the anchored ascent line. This provided directional guidance if divers ascended through the hole’s center and lacked visibility of the ascent lines. After the site preparation was complete, the deep penetration team prepared for their descent.

The dive plan called for air to 200 fsw. At 200 fsw, they switched to their bottom gas, trimix 10/50 (10% Oxygen, 50% Helium, 40% Nitrogen). This mixture provided the divers with a partial pressure of oxygen (ppO2) of l.66ATA at the maximum planned depth of 500fsw. The bottom gas also provided the deep team with an Equivalent Narcotic Depth (END) of 236fsw.

The deep team comprised Frank Richardson and Curt Bowen. They each wore double 121s filled with air on their back and two single 80s filled with trimix clipped to their sides in a cave configuration. The team staged Nitrox 40 at 100 fsw and 100% O2 at 20 fsw. Safety divers protected the deep team by stationing themselves at 300 fsw, 170 fsw, 50 fsw, and the surface.

The divers’ first of two deep penetrations took them to the sinkhole’s lip, where they attached a guideline and reel to prepare for entry. They descended at a rate of 50 feet per minute. The divers found the silt mound at a depth of 394 fsw. They explored briefly, reaching a maximum depth of 405 fsw. The silt mound sloped gently outward, so they speculated the bottom was probably not too much deeper.

During the ascent, survey measurements and drawings were made for mapping. The ascent rate of 33 feet per minute allowed ample time for these measurements to be taken. The total ascent, with decompression, lasted 175 minutes. Divers made the first decompression stop at a depth of 220 fsw, signaling “OK” to the deep safety.

The divers accomplished decompression on ascent using trimix to 200 fsw, then switching to air. Divers used air from 200 fsw to 100 fsw, then switched to staged Nitrox 40. Divers used oxygen at the 20fsw and 10fsw stops.

After the dive, the team met to discuss the dive and plan for the second penetration. The next day, Curt and Frank used the same dive profiles to descend to the bottom. A quick survey of one wall during this dive confirmed their suspicions about the maximum depth. The deep team found 435 fsw to be the deepest spot in the sink. With the Green Banana’s maximum depth revealed, the team set off for port.