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This very early telegraph cable connected Havana, Cuba and the United States in the late 19th Century. It was recovered from the Atlantic Ocean by Tom Perera in January of 1997. It was conserved in an electrolytic bath for 4 months and then cut into smaller pieces and carefully dissected to reveal its inner construction.
The various layers of the cable are shown and described below:
OVERVIEW OF THE CABLE AND ITS LAYERS:
This view shows all of the various layers of the cable. Each of these layers
is described below. Some erosion of the outermost layer is apparent due to its
submersion for over 100 years in salt water.
OUTER LAYER - 1: STEEL WIRES:
The outer layer consists of a total of 10 strands of steel wire. Each strand
had an outside diameter of 3/8-inch. This layer was designed to provide great
strength and resistance to abraision from coral and rocks.
LAYER 2 - TAR-IMPREGNATED HEMP:
This layer was designed to provide a waterproof seal. It was wound in
the opposite direction from the outer layer in an attempt to reduce torsional
twisting of the cable.
LAYER 3 - SPIRAL-WOUND COPPER SHEET:
This copper sheet layer was included to prevent the Torado
worms from working their way into the Gutta Percha insulation and allowing
salt water to short out the inner conductor. Although it looks like
the shield in a modern coaxial cable, it actually had no electrical
LAYER 4 - SPIRAL-WOUND COPPER SHEET:
A second layer of copper sheeting was wound just under layer 3. It
was also designed to further deter the Torado worms.
LAYER 5 - GUTTA PERCHA INSULATION:
Gutta Percha is a rubber-like Malayan gum obtained from trees which is
liquid when heated and solid when cool. It is an excellent insulator and was
used as the main cable insulation.
LAYER 6 - SPIRAL-WOUND STEEL WIRE:
A continuous wrapping of .020-inch. diameter steel wire provided inductive
loading to partially cancel out the large values of capacitance generated in
such a long cable. Cancelling out some of the the capacitance reduced the
time-constant of the cable and increased the speed that It could carry
LAYER 7 - SPIRAL-WOUND COPPER SHEETS wound around the
LAYER 8 - SOLID COPPER INNER CONDUCTOR:
The 5/32-inch outside diameter layer of spiral wound copper sheets
decoupled and isolated the steel wire from the 1/8-inch outside diameter
solid copper inner conductor which carried the positive and negative voltages
of the telegraph signals.
In the future, I plan to add information about the electrical characteristics of this cable. I will also update these pages as I try to recover all six of the underwater cables. They will provide samples of the technological improvements in cables from 1866 to the 1900's and allow me to analyze how well they have survived over 100 years under the ocean.
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