Oil in the ocean is a sensitive subject these days, but in the late 1800s, steam ships had stocks of oil specifically set aside to dump in the ocean. This may have saved people's lives. We'll tell you why.
Late 19th-century steam ships carried oil aboard. They didn't limit themselves to one type of oil, but made sure to stock vegetable oil, mineral oil, and even, as this was the 1800s, sperm whale oil. They made absolutely sure that lifeboats were equipped with cans of oil.
Ships kept this oil not for cooking or lighting, but because it could calm violent seas. They didn't know quite why, but they knew it worked, and each captain had their own secret. One book, "The Use of Oil to Lessen the Dangerous Effect of Heavy Seas," is paragraph after paragraph of which captain used how much oil where to calm what kind of storm. (A worrying number of them include the detail that the captain had "a boy" stand at the front of a ship in heavy seas trickling oil into the oncoming waves.) A little oil and the breakers disappeared. Ships that were taking on water with each wave suddenly could keep their decks clear. They could master storms.
The practice of oiling up the sea to tame the waves did and does work. A small amount of oil, sometimes less than a gallon per hour, will calm the water around a ship. The deep ocean swells don't change, but the waves aren't as high and they usually stop"breaking" - curling over on themselves and on ships.
The oil accomplishes this by doing exactly what it does in salad dressing - forming a film over the denser water. Even if this film is very thin, it does a critical job. Air doesn't slip frictionlessly over water. It slightly adheres to the surface of the water. If air is blowing fast over the surface of water, it will tug the water molecules along with it.
The force, though slight, builds up when it comes to air being moved at tens, or even hundreds, of miles per hour over huge swaths of ocean. The traction of the air builds the waves up, and as they get more vertical, the friction between them and the horizontally moving air increases. They build, curl, and break, sometimes over the deck of a ship. But not once oil gets involved. Air doesn't have as much traction with oil, and even when it moves the oil, the oil simply slips over the water. It acts as a kind of sheet, protecting the ocean from the effects of the air.
What's more, if water does "break" over a layer of oil, it immediately loses energy. The oil is less dense than water. Dense water on top of oil sinks through it. This saps energy from the storm. It may only be a little bit, but if you're a 19th century sailor, every little bit helps.
There's even some evidence that oil slows the wind during a violent storm. Water droplets kicked up into the air might form a vapor layer that cuts turbulence and allows air to move more quickly over the ocean. Oil forms a film over the sea that discourages water drops from forming. One scientist believes that we might calm hurricanes by dumping small amounts of non-petroleum oil on the ocean. (Other scientists vehemently disagree.)
These days, ships are meant to have as little impact on the ocean as possible, and so oil-dumping is discouraged. Still, ships do put off oil, and it is often possible to track them by the trail of becalmed sea that they leave behind them.
If you want to test this idea without being - rightly - castigated by environmentalists, don't go to the ocean. Just find yourself a puddle on a windy day. No puddles where you live? Try a wide bowl of water on a windy day. There aren't any deep swells in a puddle, but you'll notice there are a lot of wind-created waves. Take a very small amount of vegetable oil and add it to the puddle. You really can do this one drop of oil at a time. You'll notice that, suddenly, the puddle becomes calm and the waves disappear.
Congratulations, you are now a master of the waters.