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Bell Design

How the Chestatee Diving Bell Operated

by Manuel B. Carvalho

1.0 Historical Background

An early diving bell.
The Chestatee River Diving Bell is a unique maritime artifact used for underwater gold mining.  Its technology, however, is rooted in the ancient past since the desire to go under water has probably always existed: to hunt for food, uncover artifacts, sunken treasure, repair ships (or sink them!), and perhaps just to observe marine life. Until humans found a way to breathe underwater, however, each dive was necessarily short and frantic.

A diving bell is an airtight chamber that is suspended underwater as a workstation for a single or multiple divers; it will refresh divers with air without having to come to the surface, allowing a diver to remain underwater for extended periods of time. A diver could leave the bell for a minute or two to collect sponges, pearls or explore the bottom, and then return for a short while until air in the bell was no longer breathable.  The diver uses this reservoir of air to stay underwater longer than would otherwise be possible.

In its simplest form the apparatus is named for its resemblance to a bell, in that it is narrow at the top and open at the bottom.  The concept of a diving bell goes as far back to the ancient Greeks. Aristotle (384-322 BC) wrote about such a device in book XXXII of his Problems saying that “ they enable the divers to respire equally well by letting down a cauldron; for this does not fill with water, but retains the air, for it is forced down straight into the water.”

Alexander the Great in a diving bell
Da Vinci's concept

According to legend the Macedonian King, Alexander the Great, used demolition divers to remove underwater obstacles from the harbor during his famous 1332 BC siege of Tyre (Lebanon).  It’s reported that Alexander himself made several dives in a glass  diving bell in order to observe the work in progress as depicted in the 16th century painting at the left.

During the Renaissance Leonardo DaVinci describes, in his book “Codex Atlanticus”, a breathing apparatus that allows a diver to remain underwater for long periods of time. In 1535 the Italian physicist, Guglielmo de Lorena, used a diving bell from a design by Leonardo da Vinci to recover sunken items from two of Caligula’s sunken galleys from the bottom of Lake Nemi.  The device was basically a large "bell" that rested on the users shoulders and had a tube running from the surface into the bell that piped fresh air in so the inhabitant could breathe.

Halley's air replenishing system
Diving bell design wouldn’t reach its climatic point until the 17th century when Dr. Edmond Halley, of the comet fame, improved the design by utilizing an air replenishing system to overcome the effects of atmospheric pressure. The engraving at the left from the National Maritime Museum, London depicts the use.  

Air was added to the bell from separate lead weighted barrels lowered from the ship above.  A hose from the barrel led to the bell, where a diver inside the bell could simply turn a valve to allow fresh air  from the barrel as water filled in through a hole in the bottom forcing the air up and out into the bell. The barrels were pulled to the surface for refilling and dropped back in. By this means almost all the water could be expelled from the bell, allowing the divers to operate in almost dry conditions. Warm stale air was expelled from an orifice at the bell top. Halley’s bell worked in typical depths of 20 to 60 feet. 

 The English scientist John Smeaton invented a workable diving air pump in 1788 which replaced the barrels.
Throughout the nineteenth century various designers built bells of ever-increasing size and complexity.  These later bells were made of cast iron and very large and heavy compared to the traditional wooden diving bells.  Although the diving bell allowed for the exploration of underwater depths longer than any other apparatus its main disadvantage is that it needed be pulled up to the surface for the workers to be replaced which is a time and energy consuming process. 

Later designs connected the diving bell with the surface by means of a turret that served as an air-lock. Personnel and equipment could then pass through the airlock, equalizing pressure, on their way to and from the diving-bell. These bells are also known as Caisson bells but the terms are often used interchangeably. The earliest air-lock design [ref 1] apparently is due to John Williams of Exeter, England who in 1691 petitioned a patent for a "submerged chamber. communicating with the surface by a rigid tube, up and down by which persons might pass."   Further improvements continued such as those by Col. Pasley [ref 2] who, in the early 1850's, proposed to attach boat shaped ends to a diving bell in order to prevent the considerable vibrations when diving bells where used in rapid moving streams.
The Dublin Dock Diving Bell

In 1862, Bindon Blood Stoney, Chief Engineer of Dublin's Port and Docks, proposed using a 90 ton bell as part of a process for deepening and laying huge cement blocks for the foundation of the North Wall Harbor in Dublin, Ireland making it a deep water port.  The bell chamber was rectangular box twenty by twenty feet, with six and a half feet of headroom inside.  The overall height of the bell including the three foot diameter shaft and airlock chamber was forty-four feet.  Working in compressed air may not have been fully understood by the crews working in the bell as there are several accounts of men suffering with ear trauma and bleeding from the nose and ears.  The project was completed in the mid-1880s but the bell was used several other times until the 1950s.  Today, the restored bell, seen at right, stands in Dublin's  Sir John Rogerson’s Quay. 

The Brooklyn Bridge Caisson
New York’s Brooklyn Bridge, considered one of the Seven Wonders of the Industrial World, used a caisson diving bell, basically large open bottomed wooden boxes, shown at left, for
Brooklyn Bridge Caisson Work Area
the construction of its pier foundation.  The work of preparing the site of the foundation of the Brooklyn tower was commenced January 3, 1870 using an oblong form caisson measuring 102 feet by 172.  Its top was 22 feet thick made of dense Southern pitch-pine in timbers twelve inches square.  The bolts and angle-
irons of the massive
 3,000 ton device alone weighed 250 tons. 

Workers, 30-50 per each eight hour shift, entered the caisson through an air lock tube to reach the pressurized work chamber, shown right, where they
dug away at the sand and rock on the river bottom until reaching bedrock 78 feet below the surface.  Stone was added to the top of the caisson as it went down 
and it eventually was filled with hydraulic concrete becoming a permanent part of the tower foundation when the project was completed in 1883.


2.0 The Diving Bell

The Diving Bell today.
It is in this technological milieu, where diving bells have been used to lay harbor and lighthouse foundations, building docks, deepening harbors and the salvage of wrecks, that Philologous H. Loud in 1875 acquires his Diving Bell for mining gold from the Chestatee River bottom gravels.  Where and when this idea exactly came to him we can find no documentation.  It is known that in 1852 the San Joaquin Diving Bell Company attempts to use this method during the California gold rush.  Loud being an educated man plus the history of gold mining in the family [A Loud Gold Mining Company still exists today in White Co., GA] it’s easy to imagine that the thought could have easily come to him.  This would be particularly so after the Civil War and the difficult economic conditions generally throughout the South.  The mix was right for trying to enhance the family’s net worth in a unique way.  

What is known is that in Aug. 27th, 1872 the Georgia Legislature incorporated the Georgia Gold Mining Company with $10,000 in capital stock and gave the exclusive right to Loud and four other people to work for precious metals on any state property for a period of thirty years.
  In 1875 the machinery for the Diving Bell arrived in Dahlonega and a boat to carry it was built of Southern Yellow Pine.  The diving bell is constructed of ¼ inch boilerplate iron panels forged at the Pottstown Iron Works in Pottstown, PA according to forge marks on the panels. The panels are shaped and riveted together to form air tight joints. The front of the bell is wedge shaped in order to break river currents and reduce turbulence inside the bell.  A pressure equalizing entry tube with two inner doors allows workers to enter the bell.  Inside the bell's working chamber is an inner chamber used for ballast needed to weigh down the bell in order to sink it below the river surface. Five fixed portholes mounted on the top of the bell and one on the entry tube allow for light to enter inside the equipment.  There is no bottom on the bell.

The bell, less the entry tube, measures 6 feet wide by 14 feet long and 8 feet high.  The whole craft weighs a bit over 5,000 pounds. Who designed the bell and where it was fabricated is not known.


3.0 The Diving Bell Boat

The diving bell boat remains a wreck in the Chestatee river and has not been fully seen since October 1876.  It has yielded only some of its secrets to direct observation by the authors.  The boat is a barge type design that measures 17 by about 50 feet.  A well, 
 slightly larger than the bell, located towards the center of the boat deck allowed the bell to be raised and lowered. 

A wench drove the bell up and down. Using four hooks on the side of the bell a rope or wire rope connected to the wench via two
 sets of block and tackle within the timber support structure above the bell.  The rope was routed from the block and tackle through pulleys, two on each side of the bell well, to another double set of pulleys at the front by the wench. The rope was then wound on the spindles of the wench.  When the wench rotated the rope wound around its side spindles and, depending on the direction of rotation, the bell was either lowered into the river or brought up into the bell well.

The wench was powered by a steam engine that has not been located and its exact specifications are unknown.  Full exact measurements are not know because the boat is partially buried under the river bank and covered by a large quantity of sand and silt.  The rear section of the boat has not yet been seen and remains covered with about four feet of sand.  About 15% or so of the left front side remains buried under the bank.  However, the top view of the boat, including underwater photos of still attached machinery, is something like this:

 

  
Additional equipment for working the gravel – a sluice box, for example – in order to extract the gold and possibly a roof would also likely be present but not shown in the simplified diagram.   None of the engine machinery has been discovered.  It's likely that it was all removed along with the tools in order to satisfy liens placed on the equipment.  The pulleys and parts of the wench have been found still mounted on the boat as shown in the images in the boat diagram.  The wench itself was yanked off the boat in 1983 when the bell was forcibly removed from the boat.

4.0 Operating the Diving Bell

Loud's Diving Bell Patent
There are no known diagrams, schematics or photographs from this era related to the diving bell and its boat.  However Loud never stopped thinking of his idea because in 1883, seven years after his failed attempt, he patented [no. 272, 722] an improved diving bell design.  The  major improvements are the addition of a stamp mill, marked with a red X in Figure 1 to the left, and better support which may be ignored for the moment but the overall design provides a prospective look at what the actual diving bell looked like. It would likely have a similar support structure and set of block and tackle pulleys to move the bell up and down through the well.  Eyewitness accounts of the bell being pulled out describe seeing block and tackle.

In order to push the water out of the open bottomed bell, compressed air was pumped into the working chamber as it was submerged into the river.   Once at the bottom the pressurized air would not only keep the water level at the miner's feet, it would also  maintain a fresh air environment for them to work.

When the men wished to enter the bell they passed through the top hatch and descended using a ladder secured to the side of the entry tube.  Once the hatch was closed they equalized the pressure of the entry tube to be the same as in the bell's working chamber.  They could then open the lower hatch and pass safely into the bell, closing the door after them. When returning to the surface, they reversed the operation, opening the lower hatch, entering the entry tube compartment and closing the hatch.  They would then open a valve to release the air pressure and exit to ambient atmosphere through the top hatch.

Once at the bottom the miners would spade up the gravel into a suction tube, labeled R, in order to bring the gravel up from the river bottom into the boat to be worked in the sluice box and extract the gold.  Although no actual physical evidence of the suction tube has yet been found there is a newspaper account that describes it.  Mr. J. A. Burns discusses the diving bell operation in a letter extoling the virtues of Georgia to the Calaveras Citizen newspaper in California and reprinted in page 1 of the June 16, 1876 edition of the Dahlonega Mountain Signal.  In his letter, Mr. Burns describes the diving bell operation consisting of “a monster boat, on the Chestatee river.  It works by steam, and has a large iron caisson, which is lowered into the water.  The air soon forces the water all out, and then the men go to work in the river-bed and shovel the gravel to large pumps, which take it up to sluice boxes, water for which is raised at the same time.”

The addition of the stamp mill to the diving bell in Loud's 1883 patent design is likely indicative of operational difficulties with the suction tube.  It's likely that the tube was smaller and probably became easily clogged.  The addition of the stamp mill to break up larger rocks into smaller particles is likely an improvement by Loud to get around this operational problem.  The suction tube is also an integral part of the craft unlike the Diving Bell which has no ports for such a device.  It's likely a flexible hose under the Diving Bell was used to take the gravel up to the boat.

To lower the diving bell to the river bottom and stay there, the buoyancy of the air trapped within it would have to be overcome.  This was accomplished by placing material within the ballast inner chamber to weigh down the diving bell.  Newspaper articles of the time indicate that it took 22 tons of sand ballast to sink the bell.  This is in agreement with current calculations that indicate that it would take at least 15 tons of weight for an object with the surface area comparable to the diving bell to just break the surface of the water.  It's likely that this was a major technological flaw in the bell operation since it would require either removal of the ballast or tremendous force from the wench to raise the bell from the bottom of the river.  Diving bells of that era typically used water in a sealed chamber to serve as ballast.  Such a tank is easily filled and emptied by using compressed air unlike the Diving Bell's ballast chamber which used a solid material as ballast.  While there are sliding panels at the bottom of the ballast chamber which could be used to empty it as the bell raises, filling the chamber for another descent must have been a tedious and cumbersome affair.  However, Loud makes no improvement in this perceived problem in his patent.  It's possible that using sand as a ballast was not much of an operational problem with his large and likely powerful wench.  On the other hand, perhaps he didn't have sufficient operational time for this to become a problem.  The boat and the diving bell appear to have been operational for only a few months.

5.0 Conclusion

A possibility of what Loud's boat and bell looked like.
As previously stated there are no known diagrams of the Diving Bell and its boat.  However, it can be imagined by what has been discovered thus far that it must have looked very similar to the diagram on the left.   At the rear of the boat the diagram shows a submerged diving bell below its support structure.    In the middle is a steam engine, a boiler and an air compressor.  On the sides, labeled R, is a sluice box for separating the gold from the gravel.  In the front is a wench, which in this case, also is used to settle the bell and move it slightly when necessary.  This image, which when clicked will show a larger view, is from an 1898 patent whose major aim is to provide a better seal between the bell with the river bottom.  From the known information available it is very likely the P. H. Loud's diving bell and boat were very similar to this design.

P. H. Loud took the first dive into the murky waters of the Chestatee River in November of 1875.  He emerged thinking that a fortune was within easy grasp and that he would build more boats to collect it. Unfortunately, bad weather, poor finances coupled with likely difficulties in Diving Bell operations resulted in legal problems that caused all operations to cease.  These unfortunate circumstances culminated when the boat sank in October of 1876.  The dreams of Loud Mining Company went with the boat.  Today the Diving Bell remains as a monument to these dreams and perhaps to inspire others who dare to do something new and different.  One might not always succeed, but like Philologous H. Loud don't ever give up.




Posted 3 Apr 2012
16 Apr 2012: Boat diagram was modified due to new information from Bill Waldrop's dive on the boat during the April 13, 2012 weekend.


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