Boats fascinate me. I think it’s because some of my favorite books as a kid were the Swallows and Amazons novels by Arthur Ransome, which are full of boats. So, “Jibbooms and bobstays!”, I said to myself, “Why not write about them?”
The one characteristic you really, really want in a boat is the ability to float. The scientific principle behind all floating is Archimedes’ Principle, named after the famous Greek philosopher who formulated it in the bathtub and ran naked down the street yelling “Eureka!” An object floats if the amount of fluid it displaces matches its weight. How deep a boat sits depends on how much water it has to displace to match its weight.
Our ancestors didn’t know Archimedes or his principle, but they knew that logs float, so hollowed-out logs were the earliest form of boats. They worked well, too, because they were long and narrow and therefore moved easily through the water . The Caribbean Indians called their log dugouts “canaoa,” which is where we get the word canoe.
When people wandered to areas where no large trees were available, they began to build boats with animal hides fastened over a wooden frame: kayaks, for example. They were more seaworthy than dugouts because they flexed with waves instead of resisting.
When the first people to populate North America came across the Bering Strait from Asia, they knew how to build hide canoes, but in the eastern forests large game animals weren’t that plentiful, and the powerful currents of the region’s rivers strained hide-skinned canoes. Hence the switch to birch bark, a stiffer, but still flexible, covering.
Just as canoes were the first form of boat, so the paddles that drove them were the first form of boat propulsion. Paddles work because of Newton’s famous Law: for every action there is an equal and opposite reaction. When you drive a paddle backward through the water, the water pushes back, shoving you forward with the same force you applied to the paddle. Oars were eventually used to drive even large ships like the Greek triremes, but long before that people had figured out a far less tiring form of propulsion: the sail.
The earliest type of sailing craft was just a flat raft with a short mast and a single square sail, steered by an extra-large oar slung over one quarter (for which the word steerboard was coined– hence the term starboard for the right side of a ship).
The principle of the sail is pretty obvious: air blows the sail forward and takes the boat with it. But nobody could sail into the wind until the 12th century, when the rudder was invented,. Sailors discovered they could sail “close-hauled,” angled toward the wind, and thus advance into the wind by zigzagging back and forth, or “tacking.” This works because the force of the wind against the sail is matched by the resistance of the water to having the boat’s keel and rudder pushed sideways through it. The boat, trapped between these two forces, squirts forward like a watermelon seed squeezed between two fingers.
When steamboats came along in the late 1700s, they were propelled by paddle-wheels, but in the 1830s Archimedes’ screw (yep, the same Archimedes), a sort of auger originally used to pump water, was applied to boats. Screw-type propellers screw the boat through the water like a screw going through wood. Bladed propellers are more like rotating wings, curved so that, as they rotate, the water flows faster over one side than on the other, creating an imbalance in pressure that drives the boat forward.
Today, gasoline engines have replaced steam engines, and the most popular form of motor is the outboard, which is light, inexpensive, and capable of being attached to a wide variety of craft, from rowboats to small cruising sailboats and catamarans.
The first successful outboard, built in 1907 by Ole Evinrude, developed less than two horsepower. By contrast, the most powerful modern outboards develop up to 300 horsepower. Inboard motors, in which the engine is firmly attached to the hull and drives a long shaft with a propeller on the end, range up to 1,200 horsepower, and there are also inboard/outboard motors, which combine the power of an inboard with the rotating/tilting propeller of an outboard, making them good for operation in shallow water.
Today, boating is one of the most popular leisure activities, but of course boaters generally aren’t thinking of Archimedes’ or Bernoulli’s Principles or Newton’s Third Law or even Archimedes’ screw. The only principle that concerns them might best be called Ratty’s Principle, for it was Ratty, in The Wind in the Willows, who said that there’s nothing whatever half so worth doing as simply “messing about in boats.”
Unless, maybe, it’s writing about them.
