Cross Section View of Forty Fathom Grotto

Tuesday, 3 October 95, South Florida - I visited Divers Unlimited, a scuba dive shop in Hollywood, Florida (800-289-DIVE), to sign up for a dive. They are located on Hollywood Beach Boulevard, just east of the Florida Turnpike. While I was there I asked for and was given a tour of their nitrox filling station. The shop filled scuba cylinders with prefixed nitrox inspection labels by mixing the gas in cylinder. I found the same is true for the rest of Florida. They used four cascaded H size oxygen cylinders (300 CF) to fill the scuba cylinder with a predetermined amount of oxygen and topped them off with oxygen pure air. The shop had a booster pump, but only used it to make high pressure air. They felt that the oxygen was not expensive enough to justify a booster pump to mix nitrox. They charged $2.50 for air fills and $8.00 for nitrox fills.

Their boat was named the Diversion and was docked in Dania, Florida on A1A south of Diana Beach Boulevard. The boat leaves the dock every day at 1:00 PM. Except when I was in South Florida, I was at the dock on Wednesday, Thursday, and Friday of that week. I met a lot of nice people but didn't get to dive with them due to hurricane Opal spinning off twelve foot seas and high winds.

Monday, 9 October 95, North Central Florida - Forty Fathom Grotto (904-368-7974) is located on Florida route 327 about a mile and a half North of Alt route 27, 14 miles West of Ocala, Florida. They mix by in-cylinder mixing nitrox, heliox, and trimix. They also fill scuba cylinders with pure oxygen for off gassing of nitrogen at the safety stop platform. The grotto has a surface area equal to about six or eight "Y" size swimming pools and is covered with duck weed most of the year. It has an inverted conical shaft diverging from the surface and leading to the cavern on the east that is 240 feet deep and used for deep dive training. There are safety stop platforms in the vertical accent portion of the shaft at 15, 30, and 60 feet. At the 15 foot platform there is surface supplied oxygen for nitrogen off gassing. The grotto's water quality (visibility) is about the same or maybe a little better than Dutch Springs in Allentown. It was the poorest I found in Florida with the exception of the Crystal River's manatee snorkeling dive.

There are two ways to make a Florida cavern dive. One way is to be cavern certified and have a dive buddy that is cavern certified. The other is to dive with a divemaster who is cavern certified. The latter is probably cheaper for vacation diving since the divemasters carry lights that retail for $400.00 and know the caverns inside out. I was diving with Bob Hambridge, the manager of the Forty Fathom Grotto. He is from New England and could not deal with shoveling snow any longer, so he headed to Florida. Bob got me a 80 cf aluminum bottle of nitrox from a rack of cylinders that were previously mixed. We analyzed it and found it to contain 31.9% oxygen. This mix was calculated to have a maximum allowable working depth of five atmospheres or 136 feet of fresh water. A dive was planned that would not exceed 110 feet. Using 110 feet for calculation purposes, the equivalent air depth for nitrox 32 calculated to be 89.9 feet of fresh water or 90 foot tables. Bob dove with twin 72 cf steel tanks with the same mix and redundant regulators. We entered the water from a submerged surface platform and dove down to the fifteen foot safety platform, adjusted our weight belts and BCs, and then checked our lights, since this was basically a night dive. Even though it was Monday morning, as we descended the sloping wall of the grotto we dove into nighttime. After the thirty foot level a vertical ascent is no longer possible. At the hundred foot level (which is marked by a horizontal line) you're in total darkness with the exception of the lights you bring with you. Working as I do in public works pipeline inspection, I am probably more aware of the hazards and safety precautions for proper confined space entry than the average recreational scuba diver. So it was a little strange being in a dark overhead environment without wearing a hard hat, and I still looked for structural defects in the cavern ceiling over my head. At the hundred to hundred and ten foot level the grotto is a paleontologist's playground. It is made up of metamorphic rock that sheared during the formation of the grotto and exposed the fossilized remains of prehistoric shellfish. With the right equipment you could spend hours photographing these fossils if you were willing to dive with nitrox filled twin eighties and then spend a few more hours on the safety platforms breathing surface supplied pure oxygen. After circling the grotto at the one hundred ten foot level we ascended to the fifteen foot platform and made a three minute safety stop on pure oxygen.

My total down time was twenty eight minutes less three minutes for the safety stop. According to the PADI RECREATIONAL DIVE TABLES twenty five minutes is the maximum allowable down time for this dive. The navy tables would allow thirty minutes, but diminish the time available for repetitive dives. The dive was started with 2900 psi and completed with 300 psi. My fifteen cubic foot pony bottle contained air which was not used except to check that it was working properly. I discussed this with Bob. He stated that some divers who dive with pony bottles containing air make excursions to deeper depths than their nitrox mix will allow. But Bob stated, "The accepted practice is to dive with a pony that is at least the same or richer mix than the main cylinder or cylinders."

Monday Afternoon - After a two hour and eighteen minute plus surface interval, making us " A " divers on the PADI tables, we set up the BMD/SCR-4 rebreather for the afternoon dive. I was to dive with the rebreather, and Bob would dive twin 72 CF steels with redounded regulators. The BMD/SCR-4 was designed and built in Canada for pipeline inspection, since the Canadians have pipe runs of ten thousand feet or more without inspection ports. In Philadelphia our maintenance crews use Scott packs since our pipe runs have man holes every five hundred feet or less. The unit was modified for scuba diving in hopes of generating additional sales. It was made up of a standard BC jacket with an additional bladder for mixing the replenished breathing mixture. The jacket was mounted on a rectangular plastic case that contained four 13 CF 2450 psi scuba pony bottles and a carbon dioxide scrubbing chamber. The breathing hoses were connected to ninety degree bends mounted on top of the plastic case. The hose diameter was the size of a washing machine discharge hose. It seemed much larger and less flexible than the two-hose regulators used to teach my original dive class. Of course it's been a few years since that class.

Bob Hambridge & The BMD/SCR4

I was seventeen then and my memory of that period is not very clear. This unit contained four pounds of carbon dioxide scrubbing material which was milk white and crystalline in structure. Its retail value was about a dollar a pound. We dumped it and replaced it with fresh material for the dive. This particular scrubbing material contained sodium hydroxide (NaOH), a compound that when mixed with water forms a caustic cocktail commonly referred to as liquid plumber. If you exhale more than a moderate amount of water into your mouth piece you may have a problem diving with a rebreather. This unit was referred to as a semi-closed circuit rebreather because it dumps 25% of your exhaled breath. Therefore the fifty two cubic feet of gas in the unit are theoretically equal to a two hundred and eight cubic foot scuba cylinder. Now bear with me as the theory gets a little complicated from here. If you don't like my explanation take it up with Howard, who suggested I go swimming with this thing on my back that weighs about the same as twin 72s. The dive cylinders were filled with nitrox 32, but for calculation purposes nitrox 28 is used to find the equivalent air depth and maximum allowable depth. On the face of it that doesn't seem to make too much sense, but 75% of what you are breathing is exhaled breath, which is oxygen depleted. Through testing, the depletion was found to be 4%. Therefore, the unit could be filled with heliox, nitrox, or trimix as long as the oxygen depletion was taken into account. With this in mind, what happens if the unit were filled with air (nitrox 21)? The Philadelphia Water Department's bidding specifications define oxygen deficient air as air containing less than 19.5% oxygen. That means if you deplete 4% of the oxygen in the air you're breathing you are left with nitrox 17, a mixture not breathable at one atmosphere (the surface) or less. The unit comes with an Orca nitrox computer that is set to your mix less 4% oxygen.

Another effect of the rebreather process is that you're reusing your own hot air. Therefore, you wouldn't get cold at the end of a long dive. This is supposedly a positive feature. We started to gear up for the dive and my damn jacket didn't fit. Bob said it was a medium. I haven't been a medium since junior high school. As most of the club members who have dove with me over the years know, if this were a regular Sunday Sea Horses dive I would have backed off and not gone in the water, but this was a fifteen thousand dollar play toy that I really wanted to check out. After all, isn't the difference between men and boys the price of their toys?

So we took an old weight belt and slid it through the front belt loops of the jacket. I attached my pony bottle to the belt the same way a commercial diver carries his bale-out bottle. I eased off the dive platform at the dock with my face down in the water. I then took a real quick second breath to made sure I was really breathing. There is no second stage on a two hose regulator, so the sound we are all accustomed to of air moving though the second stage diaphragm is gone. (A little eerie at first.) I surface kicked down to the fifteen foot platform with no air in my BC. I was still a little light. I swam back to the dock and put a two pounder in my jacket pocket. We dove to the sixty foot level, added a little air to my BC, and started circling the grotto. I was uncomfortable and my breathing rate was excessive. Because my of breathing rate I kept watching the pressure gage built into the Orca nitrox dive computer. It dropped very slowly - after all I was swimming the equivalent of a two hundred and eight cubic foot scuba cylinder filled with nitrox 28. When we came to the sixty foot safety platform I swam over to it and rested for a few minutes. I was uncomfortably hot. I reached into my pocket for my slate to explain to Bob what was going on and then realized that my slate was in the pocket of my BC jacket. (Not the BC jacket I was wearing.) If I were more familiar with the equipment I would have taken off my wet suit at the platform and let it float up. The water at that depth was 66 degrees. I took the extra two pound weight out of my pocket and left it on the platform. As I continued to circle the grotto my wet suit turned into a sauna. At twenty minutes into the dive I swam to the vertical shaft portion of the grotto and made a slow vertical ascent. At a depth of thirty feet I switched to the pony bottle and continued to the surface. Upon surfacing, I would have dropped my weight belt to make the surface swim to the dock easier, but Bob was right beside me so I just took my time snorkeling back to the surface platform at the dock. At the dock I took off the wet suit and went for a swim. The surface water was 68 degrees and still felt warm.

The dive was started with 2450 psi and finished with 1630 psi remaining. This is the mathematical equivalent of breathing a 72 cubic foot steel tank down to 75 psi. In conclusion, if your equipment doesn't fit right or is not adjusted properly, or you don't feel good, don't get in the water. Remember, we do this stuff to have fun. If the jacket had fit properly I think my breathing rate would have been normal. The dive would have been uncomfortably warm due to the rebreather process, but not one that had to be aborted.

Wednesday, 11 October 95, North Central Florida - Blue Grotto located on route Alt 27 just north of Williston, Florida (904-528-5770). This was a hundred foot cavern dive that was about a half hour drive from my Uncle Dan's house in Ocala. The divemaster I dove with was named Steve. Steve is the owner's son, the area dive shop compressor mechanic, and the manufacturer of the $400 lights used for the cavern dives. He insisted the maximum weight belt for Blue Grotto be twelve pounds. Steve was diving with twin 72 steels with redundant regulars, a 6 millimeter dry suit, and no weight belt at all. In the bad old days before BC (buoyancy compensating) jackets we dove much lighter than we do today. The idea was to either pull yourself down the anchor line or to kick like hell until your wet suit compressed. You set your gear up to be neutrally buoyant at depth, not at all levels of the dive. If the divemaster was willing try it with dry suit and no weight belt, I was willing to try it with a wet suit and a twelve pound belt.

We pushed off the dive platform and surface dove to the fifteen foot safety stop platform. We tied off an eighty cubic foot aluminum cylinder filled with 100% oxygen for the return safety stop. I am not sure if it's proper or not to refer to that mix as nitrox 100. The water was pristine; the only limitations to visibility were the walls of the grotto and my eyeglass prescription. After entering the cave at the fifty foot level and shining the lights down to the hundred foot level, I flinched with a touch of acrophobia. It was as if I were suspended above a rock bottom in pure nothing. When we dove to the bottom of the cave we were a hundred feet under water and a hundred under ground. The cave is horseshoe shaped, so we could swim through and exit on the other side. There is a diving bell with surface supplied air at the thirty foot level between the entrance and exit to the cave. We stopped in the bell for a minute or two, then made a second pass through the cave. We returned to the safety platform, where we made a safety stop on pure oxygen. During the safety stop the divemaster pulled out a few packs of cheese crackers from his BC jacket pocket. To my amazement the crackers were perfectly watertight after being squashed in his BC jacket pocket for a hundred foot dive. I have had underwater flashlights and cameras leak, and even the lens in my mask leaked once--but sixty nine cent cellophane cheese crackers, they were just as dry as could be. We had to break them open on the side of the platform to feed the fish. I found the safety stop uncomfortable because I had to hold on to the platform so as not to float up due to the twelve pound weight belt. The dive was made with an eighty cubic foot aluminum cylinder starting at 3300 psi and completing with 1600 psi. Blue Grotto

Blue Grotto , Williston, Florida

requests divers to exit the cave with at least 1000 psi. My Princeton Techtronic bottom timer recorded a down time of 28 minutes which includes a stop in the diving bell and the three minute safety stop. If you check the PADI dive table you will find that a twenty-five minute hundred foot dive is not listed. However, the 1984 navy tables list a twenty-five minute dive at one hundred feet as the maximum down time without a safety stop. It's not that one set of tables is more conservative than the other. It's simply that the navy tables favor a longer first dive with less time for repetitive dives. What is important is that they are both tools for safe dive planning.

Thursday Morning, 12 October 95 - After the not ready for prime time experience with the rebreather I returned to Forty Fathom Grotto to make a dive on air with a regular eighty cubic aluminum cylinder and my trusty pony bottle. My dive buddy was named Tom. He was a dive instructor who came up from St. Petersburg, Florida to check out the grotto for student dive training. Our divemaster for the dive was named Steve (not the same Steve from Blue Grotto).

We pushed out from the submerged surface platform at the dock and dove down to the fifteen foot safety stop platform. After adjusting our weight and jacket belts and turning on our lights, the divemaster asked Tom to flood and clear his mask. After the dive I discreetly said to the divemaster, "You asked a dive instructor to flood and clear his mask for you. Why? " He replied, "South Florida divers freak out in water below 70 degrees; you have to check them out."

We left the platform and dove to the sixty foot level, where we circled the grotto and swam in and out of some of the small caverns in the side walls. My two companions were both twenty-something and fast swimmers so my air consumption was not the greatest keeping up to them. After a rather uneventful dive we ascended to the fifteen foot safety stop platform and made a three minute safety stop on pure oxygen.

The dive was started with 3000 psi and completed with 1000 psi with twenty five minutes down time including the three minute safety stop.

Thursday Afternoon, 12 October 95 - North Central Florida - Paradise Springs is marked by a faded dive flag painted on the side of a 16" x 8" cinder block laying on the side of the road at US 301 and SW 84th Street in Ocala, Florida (904-368-5746). It was about a ten minute drive from my Uncle Dan's house using a horse farmer's back road.

Paradise Springs is owned and operated by Jim and Nancy Paradiso. They are from Massachusetts and gave up snow shoveling and downtown Boston traffic to preserve this Florida sinkhole for everyone to visit. The property was purchased in 1989 from a farmer who considered the sinkhole an impediment because his cows would break through the fence around the sinkhole, fall in the water, and drown. A few of the cow skulls are still on the bottom. The bottom chamber of the spring is at the 140 foot level. Using the 1984 navy tables we planned a twenty minute dive to that depth. My dive profile was that of a "B" diver because I had less than a six hour and thirty-seven minute surface interval from the morning's sixty foot dive at Forty Fathom Grotto. That dive added five minutes of residual nitrogen to this dive profile. The tables called for a two minute safety stop at twenty feet and a fourteen minute stop at ten feet. This information was transferred to my dive slate.

The entry to the spring was about the size of a residential in-ground swimming pool with a submerged dive platform. There was an algae plume at the surface so the first five to eight feet had the visibility of Richland Quarry. Also at this level were an assortment of aquarium fish. The water temperature is about ten degrees warmer than the other caverns in the area. It stays in the high seventies all year round, being fed from a southern aquifer, so the fish do quite well. Below the entry shaft the water quality was pristine. The roof puts Crystal Cave in Pennsylvania to shame. Jim's weight belt was a series of celled lead acid motorcycle batteries wired to low voltage fifty watt kitchen cabinet light bulbs. The lights combined with the clearer than air water so that nighttime was turned into daytime. We swam side by side to the 99 foot level and then single file to the 123 foot and 140 foot caverns because the lower descent shafts were moderately narrow. The shafts were about 30 to 45 trigonometric degrees to the horizontal, making the descent and ascent very gradual and comfortable. We ascended to the twenty foot stop, and after a few minutes to the ten foot stop. Normally, long safety stops are considered boring by New Jersey divers because they consist of bouncing up and down on an anchor line, but here I just floated to the roof of the cavern shining my flashlight on the embedded fossils one by one. They went on forever and ever, each one a little different than the next. At the end of the safety stop I gave Jim the up sign. He checked his computer and signaled back three more minutes. Maybe I misread my bottom timer or in this case the computer was more conservative than the tables.

My total bottom time was thirty-eight minutes including the safety stops which almost equaled the bottom time. I started the dive with 3300 psi and completed it with 750 psi. My fifteen cubic foot pony bottle was not used except to check for functionality.

Saturday Morning, 14 October 95 - I left my uncle Dan's at about twenty of seven and arrived at the American Dive Pro dive shop in Crystal River, Florida at seven thirty AM. The shop is at 714 SE Highway 19 just above route 44 (800-291-DIVE). I wasn't due at the shop until eight-thirty so I headed up highway 19 to the north end of Crystal River where I had breakfast at The Front Porch restaurant.

Cross Section View of Paradise Springs at Ocala, Florida

It stereotypically reminded me more of southern Alabama than Florida. The breakfast special was three eggs, ham, and home fries or grits with toast for $2.60. The dinner special featured an entree of alligator meat. After returning to the shop I met up with a group of five other divers and a divemaster.

We followed the divemaster to the boat dock on the Crystal River, where we loaded a pontoon boat with our gear. The boat was exceptionally wide with plenty of room for gear and changing. It was powered by a single seventy horse power outboard. The first dive was a snorkel dive to visit a manatee that was too young to make the summer migration from the river to the Gulf of Mexico. The main herd had not as yet returned to the river for winter grazing. We anchored where the young manatee was grazing on river bottom grass. The group of snorkelers swam briskly toward the manatee sighting. Since I have reservations about taking a bath with a girl that weighs more than me, I stayed by the boat relaxing in the warm river water. I assumed that if I left the manatee alone, she would leave me alone. The divemaster was sitting on the front of the boat telling me about his last dive trip to Jamaica. All of a sudden I let out a scream and the divemaster started laughing. Like a cat rubbing against the back of a leg, the manatee rubbed herself against my back. I mean talk about an instantaneous release of wet suit warming fluid. Now while this was going on the group looking for the manatee was a hundred yards from the boat. They swam back and the manatee stayed and sucked algae off the anchor line as the group petted her. One woman lost her mask fooling around with the manatee. The divemaster told her that there was a $69 dollar special sale on masks back at the shop.

We left the manatee and headed to King Cavern, arriving there after a short boat ride. The divemaster, who was also the helmsmen, anchored in about seven feet of water. While leaning against a sign that said "divemaster accepts tips", he explained that this was Florida's safest cavern dive. He put on his wet suit, BC jacket, 50 CF Aluminum tank, and regulator with pressure gage. He jumped off the front of the boat and said, "The flag over there is the entrance to the cavern, I'll see you there!" There was no buddy system established or clip board record of the divers' names.

The shaft to the cavern was in fifteen feet of brackish water. We dove down to it with the dive master descending first. It was only wide enough to follow in single file. The shaft was about fifteen feet long angled at seventy degrees to the horizontal. Though you could see the dim light of the exit shaft from most of the cavern, it was still nighttime without flash lights, with the exit shaft being like the exit sign in a dark movie house. There was a large blue point crab that measured about the size of my hand span point to point perched on a rock. I had the divemaster take my picture with him. The crab didn't make a good dive buddy (he wasn't diving with an octopus). There weren't any fossils embedded in the rocks, just some graffiti. While swimming through the various rooms in the cavern the deepest spot I found was fifty feet. After twenty minutes the divemaster waved his flashlight for everyone to get out of the cave. I started the dive with 3300 psi and completed it with 1700 psi in an eighty cubic foot aluminum tank. Back at the boat the ladder was not designed with a portly forty-something diver in mind. It only had two rungs extending below the water line. Well, I couldn't make it up the ladder so I took off equipment and passed it up to the divemaster. I told him this would be a great ladder if I could hold my breath longer or had disposable dive gear.

Saturday Afternoon, 14 October 95 - North Central Florida, Marian County park and boat ramp, on route 41 about a mile north of Denellon. The boat ramp is about twenty-five miles inland from the Gulf of Mexico on the Rainbow River. The county collected two bucks from me for the privilege of parking my Buick on the park grounds. They also rent canoes and inner tubes and have a roped off swimming area. At the boat ramp you could see straight down though ten or twelve feet of water. The water quality was like the Florida Keys but with fresh water.

We loaded the same type of pontoon boat as on the Crystal River and headed upstream. The current was about one mile per hour. We stopped at the end of the park property several miles upstream. Three other divers and I entered the water at this point. The game plan was to stay within sight of one another and swim with the current downstream as the divemaster (helmsmen) backed the pontoon boat down the river in front of our bubbles. The dive could have been a field trip for a freshmen class of hydrologists. The river was being recharged by super clear ground water percolating the sand at the bottom and entering from some small caves on the side. This was a spectacular sight that I had only read about in text books. There were large schools of shad and a few turtles. We swam a total of one and three quarter miles. I started the dive with 3500 psi and completed in with 1000 psi. The maximum depth was about twenty-five feet.

Tom Brady - Kings Cavern 1

In conclusion, Florida cavern diving may not be for everyone. If you loose your mask or your flashlight a free vertical ascent is not an option, as it would be on New Jersey night dive. Also, it is probably not worth making a special trip to this area of Florida just for the diving, but if you are in the area I would definitely consider it. (I.e. two hours from Disney World in Orlando)

As for the rebreather, I think I can wait for Decor or US Divers to build one!