In the ancient world, what is now Saudi Arabia's Tarut Island provided an important link in the trade of that era. The principal town of Darin was a terminus for ships from India and Ceylon bearing cargoes of musk—that precious, sweet-smelling product which played such a surprisingly vital role in the lives of our ancestors. From Darin, these products were loaded on camels and carried westward across the deserts of Arabia to the Mediterranean coast and thence into Europe.
Today, just outside the Bay of Tarut, another island plays an equally significant role in the economy of the modern world. But this new island is man-made. Called "Sea Island," it is part of the oil shipping terminal of the Arabian American Oil Company (See Aramco World , May-June 1966). Indeed, by last fall, when a fourth unit was added. Sea Island, with an overall length of 1.1 miles, berths for eight supertankers and a loading capacity of 439,000 barrels of crude oil an hour, had become one of the largest offshore oil loading facilities in the world.
The fourth unit—called Sea Island 4—started out as a specially designed barge built in the shipyards of Shikoku Island in Japan. The barge was loaded with miscellaneous equipment—including 10 long caisson legs on which the .unit would eventually stand—and towed some 9,000 miles from Japan to Bahrain in the Arabian Gulf, a voyage that lasted 40 days.
In Bahrain the legs were hoisted to a vertical position, inserted and lowered 24 feet into the water. As they are 215 feet long, this still left most of their length protruding straight up from the top of the barge platform like so many smoke stacks. A control house was also installed—on a tower 120 feet above sea level—and piping was added. Then, looking rather like a ten-legged table floating upside down, the whole complex was towed across the shallow waters of the Gulf to its final destination off Ras Tanura on the eastern coast of Saudi Arabia.
Once they had it in position, the engineers and marine construction experts lowered the legs to the sea bottom 90 feet below, jacked up the platform 37 feet above sea level and hammered the great legs into the bottom with a pile-driver able to slam those legs downward with 120,000 foot-pounds of energy once every second.
At Ras Tanura, the rest of the complex machinery that makes Sea Island 4 practically self-sufficient was installed Twelve hydraulically operated Chiksan loading arms were lined up, six to a berth. Eight of these arms (which link a tanker's manifold valves to the island's loading lines) are 24 inches in diameter, making them the largest marine loading arms in the world. They are highly flexible and can rise and fall as far as 90 feet—to accommodate the differences between empty tankers and fully loaded tankers at different levels of tide.
In the middle of the deck a 221-foot crane rises into the air with a jib boom 167 feet long and strong enough to lift nearly 14 tons. Control towers and floodlighting and fire-monitoring towers were erected at the corners, the crane and control towers were linked to the control house with elevated bridges and the control house to the deck with an elevator, one of the very few in the Gulf region.
The master piping, on deck and running underwater to the shore, is enormous—four feet in diameter. And because the underwater lines are encased in concrete, to keep them anchored to the bottom, they're exceptionally heavy: one foot of pipe weighs 1,000 pounds and the valves go 23 feet high and weigh 11 tons each.
From above, Sea Island 4 looks something like a giant water insect with a body like a needle—actually a narrow 1,750-foot walkway over the water—and short appendages protruding symmetrically from either side. These appendages are the six mooring dolphins, to which the loading tankers are tied, and the four breasting dolphins, which absorb the impact of the giant ships and hold them, as it were, at arm's length from the loading facilities of the main platform. The walkway and the mooring dolphins are designed to take up to two feet of horizontal movement. The breasting dolphins are capable of deflecting under impact up to 6 feet 6 inches.
History, they say, repeats itself—but with a difference. Although petroleum is not musk, it has placed the little island of Tarut, now largely a fishing and farming community, once more on the great trade routes of the world and made Tarut Bay a major link in the modern economy of oil.
John Sabini writes for the Public Relations Department of the Arabian American Oil Company.