The Bird in the Waterfall by Jerry Dennis and Glenn Wolff

Oil on the Water
Jerry Dennis & Glenn Wolff

According the folklore of the sea, oil calms troubled water. In popular use the expression refers to the way that tact or gentle reasoning can soothe tempers and restore calm after an argument. But the expression is also literally true.

In traditional seamanship, the best way to calm a choppy sea was to fill a canvas bag with rags that had been soaked in cod-liver oil or Oil Slickwhale oil and hang it over the side of the boat. It was important to use fish and animal oils -- petroleum did little or no good -- and to allow it to spread slowly, drop by drop across the surface. Even an amount as small as half a gallon an hour was said to calm the water for a hundred feet or so around the boat. Small waves were eliminated altogether and the crests of larger waves were rounded and prevented from breaking.

Although no ancient mariner could have known it, waves are flattened by a thin layer of oil because it forms a membrane that remains strong and flexible even when only a millionth of a millimeter thick. The membrane, though just a few molecules in depth, adds to the natural surface tension of the water and dampens the energy contained in waves. The secret is to keep it thin: A thick layer of oil actually has less surface tension than a thin layer.

For centuries sailors have noticed that choppy waves can also be subdued, though for a different reason, by a good hard thrashing with rain. The impact of a single raindrop striking the surface of a body of water creates a splash followed immediately by a tiny eddy beneath it. When the entire surface is covered with such splashes and eddies their combined turbulence stirs the water beneath the surface and interrupts the organized, orbital motion of the waves. The waves then die a natural death and the sea flattens.

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