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25,000 Volts Under the Sea: Laying of the San Juan Cable (1952)
(23 minutes) [On Screen: US Department of the Interior
25,000 Volts Under The Sea A Pictorial Record of the laying of the Submarine
Electric Transmission Cable to serve the San Juan Islands]
In the spring of 1951 the San Juan Islands, off the Northwest coast of the United States,
became the scene of the laying of the world's longest single-length submarine high-voltage
cable. The project was designed and carried out by the Bonneville Power Administration.
Have you heard of the Pig War of 1870? Well, it was on the San Juan Islands, the last part
of the United States Territory on which the British flag was flown, where this war was
waged. At that time, the treaty establishing the
boundary between Canada and the United States was not definite, and a dispute arose as to
the ownership of the San Juan Island group. An American settler shot a pig owned by a
British settler. Both countries immediately moved troops on the Island of San Juan. For
thirteen years this joint occupation continued, until the boundary was finally settled in
1872 by Kaiser Wilhelm the First of Germany. An old British fort still stands today as
a memorial of a war in which no shot was fired -- except the shot that killed the pig.
The people of the beautiful and economically important San Juan Islands were promised power
a long time ago. To serve these islands, it was necessary to find a way to transmit power
from the great Federal projects on the Columbia River over hundreds of miles of high voltage
lines. Several alternate plans of service were investigated,
including a submarine cable from the mainland to Orcas Island on the north, then overhead
lines spanning the narrow reaches of water from island to island, using high precipitous
banks to obtain sufficient clearance for the long spans required.
The plan finally selected included a four and a half mile submarine crossing of Rosario
Strait, a wood pole line on Decatur Island, and another two-mile submarine cable to Lopez
Island. The core of the entire plan was the submarine
cable. To select the proper cable, Bonneville engineers investigated several different types
of designs. Final specifications called for a submarine cable covered for mechanical protection
by galvanized steel armor wires laid in a jute bedding around the three rubber-insulated
copper conductors. Each conductor was wrapped with a Monel metal
shielding tape and a little over one-half-inch wall of rubber insulation. The cable was manufactured
in one continuous 7 ½ mile length, weighing nearly three-quarters of a million pounds.
The first step in manufacturing the cable was to strand the sixty-one individual lead-coated
copper wires into phase conductors. Next these were insulated by folding rubber compound
strips around each conductor and compressing them by forming wheels. After eight separate
layers were built up, a temporary lead sheath was put over the outside to serve as a mold.
The cable was then placed in a large vulcanizing tank, in which it was cured under pressure
and heat for several hours. After the curing process had been completed, the temporary
lead sheath was peeled off like a banana skin. The conductor was then immersed in water for
twelve hours and tested with 170,000 volts DC for 15 minutes, and 49,000 volts AC for
five minutes to ensure that the insulation had been properly applied and cured.
Three of these individual Monel-type conductors were then twisted together with jute fillers
to make a firm rounded core. This assembly was wrapped with a heavy tape binder and place
on reels in 23,000 foot lengths. Factory splices were required to join the
2300 foot cable lengths. The 61 copper wires in each conductor were separated and silver
soldered. When the birdcage of wires had been individually soldered, the strands were compressed
back into a smooth, firm assembly, very little larger than the original conductors.
The individual conductors were then reinsulated with rubber tape. An electric heating strip
was wound around the joint, and an asbestos blanked wrapped around it to vulcanize the
rubber tape. These splices were tested with the same AC
and DC voltages as the original insulation. The core was covered with a cushion of jute
then wound in one continuous operation with 400 miles of quarter-inch galvanized steel
armor wire. From the armoring machine, the completed cable
was fed directly over a capstan 40 feet above the ground into the gondola cars where it
was coiled about a wooden core in the center. The cable was carried from one car to the
next by means of vertical loops, and the cars were sealed with lumber.
As a safety precaution, the gondola cars were linked with two heavy chains and a bar welded
through the coupling pin to prevent accidental opening of the coupling in the freight yards
or during transit. After a final test, the shipment was appropriately
launched by breaking a bottle of Atlantic Ocean water on the end car, and started on
its 3,000 mile trip to the West Coast. In the meantime, Bonneville engineers were
completing plans for installation of the cable. Studies of weather records of the Spring period
for the previous six years were made to determine probability of favorable weather.
This record had to be matched with tidal information, since the velocity of the water in the channel
would be one of the major factors during the cable laying operation.
To assist the Bonneville Power Administration in this problem, a special study was prepared
by the Coast and Geodetic Survey, predicting the actual velocity of the water in Rosario
Strait for each hour of the day from April 1 to June 1, 1951.
From this prediction and the weather studies, the dates of April 16 to April 18 were selected.
On these dates the tidal currents would be near zero for several hours in the late morning
and early afternoon. The main hazard in cable laying is paying
out the cable faster than the ship moves. Unless this is prevented, it may result in
permitting kinks in the cable as it piles up on the bottom of the sea, as well as the
possibility of running out of cable before reaching the opposite terminal.
To control the rate of payout of the cable, and underwater profile was made from fathometer
readings taken by the Coast and Geodetic survey. At each station on this profile, the proper
tension was calculated and the angle at which the cable would enter the water.
To control the movement of the cable ship and obtain an accurate record of its position
at all times, survey parties were to be established on shore at each end of the course and at
locations off to the side. Four such points were selected for the Rosario
crossing. Radio telephone communication was provided from each survey party directly to
the top deck of the cable ship. Readings determining the position of the cable ship were to be
taken every two minutes. In the meantime, the cable train was completing
its transcontinental trip. The manufacturers publicized the huge shipment by signs placed
on the sides of the cars. These signs read: Okonite Submarine Power
Cable; For 25,000 Volt Electric Transmission; World's Largest High Voltage Cable; Diameter:
Four and two-thirds inches Weight: 19 pounds per foot; Total Weight: Nearly three-quarter
of million pounds, one continuous cable over seven miles long; for Bonneville Power Administration
The Puget Sound Power and Light Company has installed a number of cables across the deep
waters of Puget Sound using a specially equipped cable ship. Bonneville Power was able to charter
this ship, named Puget Power, for the cable laying operation.
To test the ship's equipment, check the communication facilities and assure complete coordination,
all shore and ship crews were assembled for a trial run in Seattle's Lake Washington.
There, an actual operation of laying and picking up a mile-long piece of used cable was performed.
Meanwhile, the nine gondola cars were being spotted on the dock in Seattle for reloading
to the cable ship. The cable loops between cars had been protected
by burlap wrapping, which was pretty well worn by the time it reached Seattle.
Before removing the cable from the cars, both ends were opened up and connected for a high
voltage test to ensure that no damage had occurred during transit.
Forty-six thousand volts DC were applied to each of the three conductors for a 15-minute
period. The final test indicated clearly that the cable itself was not injured in transit.
By this time, the cable ship had been brought around to the Pier from Lake Washington, and
was spotted at the dock for loading operations. A sheave, 8 feet in diameter was suspended
over the gondola cars at approximately the same height as the capstan at the factory.
This was necessary to allow the armor wires on the outside of the cable to lay back into
place, as it had been during the original manufacturing process. In the cars, this armor
wire tended to "basket" and open up. The end of the cable was threaded through
this sheave over the stern of the cable ship. Upon entering the ship, the cable was wrapped
four times around a 92-inch diameter drum. The purpose of this drum was to pull the cable
from the cars and onto the ship. Later, during the laying operation, this drum
would be utilized for providing braking power to hold the cable back in deep water.
Immediately forward of this large drum are three small sheaves which drive faster than
the drum and thus keep the cable tight to prevent slippage.
Two cable wells were available for storage, one forward and one amidships. It was necessary
with the seven-and-a-half mile length of cable to store portions in each of the two wells.
Over each of these wells is located a large sheave, driven by steam, to pull the cable
to the top deck. At all points of sharp angle on the cable the diameter of the sheaves is
quite large, to avoid damage due to bending. In the wells, a large crew of men was necessary
to manhandle the cables snugly into 34-foot diameter coils. Five-and-a-quarter miles of
cable were stored in the forward well, which required 17 layers of better than 1500 feet
per layer. Normally, an excess length of cable is ordered
for submarine jobs. With two separate crossings it appeared advisable to keep the cable in
one continuous length, so that the remaining cable from the shorter crossing would be available
for the second, more difficult crossing. This also would allow any leftover cable to be
in one piece. A slot was cut in the top deck between the
two holes. A loop of the cable was lowered into the slot and the coiling process was
repeated in the second cable well, where the remaining two-and-a-quarter miles of cable
were stored. In this manner, the cable remained in a single, continuous length.
As each car was unloaded, the railroad switch engine spotted the next one under the large
sheave, and the operation was continued without interruption. The complete loading operation
was performed in two normal working days. The tag end of the cable was opened up, the
conductor sealed with rubber tape to keep out the seawater. Then the armor wires were
formed into a pulling eye, for use at the start of the laying operations.
Since it would be necessary to know the actual tension on the cable during the laying, a
special sheave calibrated against a strong spring was provided at the stern of the boat.
The cable was threaded under this sheave to the fantail. As the tension varied, the sheave
was raised and lowered against the spring, and indicated the tension being applied.
Overnight, the ship was towed 65 miles from Seattle to Lopez Sound. Meanwhile, ship and
shore crews were assembling at Anacortes and completing final preparations for the laying.
Early in the morning of April 16, survey, radio and work crews were loaded on small
vessels and transported to their stations. The cable ship itself was anchored offshore
from the Lopez terminal. The cable laying operation was about to begin. Although this
operation would require less than 3 hours, the preparatory work up to this moment took
more than a year of planning and preparation. A helicopter was used to carry a small light
rope from shore to ship. This rope was attached to a steel pulling line which was then drawn
to the ship and fastened to the pulling eye of the submarine cable.
A tractor on shore pulled the submarine cable from the ship into the terminal. In this operation
it was necessary to use power from the steam winches to feed the cable off the ship. During
this time the cable ship remained at anchor. School children and local residents came down
en masse to ensure an ample number of "sidewalk superintendents."
Handling and laying this cable was a rugged, he-man job, and there was little time for
relaxation or the more pleasant diversions, except -- well -- yes, there were a few girls
present. The communities in the area took the event
as an important civic affair. They selected a cable-laying queen and her princesses. In
breaking the bottle over the cable as it reached shore, the Queen cut her finger slightly.
This was the only accident during the entire cable-laying operation.
When launching formalities were completed, the end of the cable was secured to a buried
anchor on the shore, and the ship was ready to proceed across Lopez Sound.
[Boat whistle] Since the ship has no means of self-propulsion,
navigation was provided by three tugs, two secured alongside, near the stern, and one
forward. The navigation officer on the top deck of
the cable ship communicated by radio to control the coordinated operation of these three tugs.
Over the loud speakers, throughout the ship and over the radio, an announcer gave the
time every two minutes. The transit men on shore and the observers
on the ship took simultaneous readings at each of these two-minute intervals.
The shore crews transmitted their transit readings to the plotting table on the top
deck, where the information was laid off on a master control map, and the actual course
of the cable ship was thus recorded. The position of the ship with respect to the
course was made available to the navigating officer. A second crew onboard ship in the
meantime was recording the angle of the cable entering the water, the number of revolutions
of the main drum (which gave us the actual length of cable paid out to that point), the
speed of the revolutions of the main drum, the actual tension of the cable, and the calculated
tension desired at each location. It was impractical to bring the large cable
ship into the shallow water near shore, so as it approached the Decatur-Allen terminal,
the cable ship was brought to a stop in deep water. There a scow was placed in position
near the stern so that a sufficient length of cable could be laid out to reach the shore
terminal. With the measured amount of cable on the scow,
workmen bound the armor wire to prevent unraveling and sawed the cable in two.
Shore crews would be coming the next day to drag the cable up to the terminals from the
scow and backfill the ditches. The cable ship was towed around Decatur Island
to Anacortes, where it lay overnight. Early in the morning she was moved to anchorage
off the Fidalgo terminal, in preparation for the second day's laying across Rosario Strait.
Procedure at Fidalgo terminal was similar to that of the preceding day. Submarine cable
was pulled ashore by tractor, anchored, and the ship began moving across the Strait.
The crossing of this Strait, four-and-a-half miles in length and in much deeper water,
was more difficult, due to the greater tensions required, the stronger wind, and eddy currents
at the center of the channel. Because of these adverse factors, it was necessary
to operate the ship at a higher speed -- better than three miles an hour at times. Deviation
from the straight-line course was as much as 400 feet, although the total amount of
cable used in excess of calculated requirements was only 500 feet.
After completing the crossing, the cable ship was again anchored, the shore length paid
off onto a scow, and the cable pulled ashore to the terminal.
At all shore terminal structures, the cable end was split and each of its conductors was
brought out to a separate insulated terminal. On the Islands, the terminals were mounted
on wood pole structures. At the Fidalgo Island substation, the cable
was terminated on a steel frame. The protective armor wire was anchored in a cast iron casing
known as a spreader head. The three individual conductors were carried through this spreader
head up to the potheads. Shielding tape on the outside of the conductors
was protected in this portion by neoprene rubber and fabric tapes. To relieve the electric
stresses between the conductor and the ground-shielding tape, a tapered stress cone was build up on
the end of each conductor. This stress cone was then inserted through
the base of the terminal, and a porcelain bushing placed over the upper end. This pothead,
as it is called, was later filled with a compound material to keep off moisture and air. A gasketed
cap nut was attached to the cap of the pothead, and provided a terminal for the attachment
of the overhead lines. The cable was energized on July 22, 1951.
This event was celebrated by the population of the San Juan Islands at a large community
gathering, with members of Congress, civic leaders, and the Bonneville Power Administration
participating. The cable has been in successful operation since that time.
And so a promise has been fulfilled -- a promise made more than thirteen years ago -- that
someday in the future, power from the mighty dams on the Columbia River would be brought
to the San Juan Islands to light homes and provide energy for the growing industries
of the Islands. [On Screen: The End]