The first scientific principle involved in boating of any sort is the one named after Archimedes, the Greek philosopher who formulated it in the bathtub and was so excited he ran naked down the street yelling “
Once you’ve managed to construct something that floats, your next task is to make it go where you want it to go. Enter paddling and rowing, and Isaac Newton (who may or may not have rowed).
When boaters dip a paddle or oars in the water and force them back, the boat accelerates forward. This is in accordance with
(It takes less energy to move a large mass of water slowly than it does to move a small mass of water quickly, but both impart the same amount of energy to the boat—so using oars with bigger blades, or “spoons,” is the most efficient way of making it easier to row, row, row your boat.)
It takes a fair amount of effort to move a boat through the water, though, because bodies moving in fluids are subject to drag, a transfer of momentum from the body to the fluid: the surrounding fluid speeds up (it was at rest before, and now it’s in motion), and the body slows down. Boats are subject to three kinds of drag: skin drag, caused by friction between the hull and the water, form drag, caused by turbulence created by the passage of the hull through the water, and wave drag, due to the energy lost in creating waves.
Racing boats, which slice through the water with little turbulence and make very small waves, are primarily subject to skin drag. In ordinary boats, wave drag is a bigger factor. And if you’re trying to row something particularly ungainly, like a raft, form drag become a big problem. (Air resistance accounts for only a small part of the drag—unless there’s a strong head wind, which certainly isn’t out of the question on
To keep a boat moving at a constant speed, you have to keep applying sufficient force, through the oars, to overcome drag. The faster you go the more drag you encounter, which means it’s hard work increasing speed. In fact, double a moving boat’s speed, you need eight times as much force as is currently being applied—or, to put it another way, doubling the force of your rowing will only increase the speed of the boat by about a quarter.
Boats also drag some water along with them. This sets up a “constant velocity gradient,” otherwise known as shear, in the water, extending down and back from the bow at an angle. In shallow water, particularly at low velocities (which allow more time for the shear layer to grow), the shear layer can actually touch the bottom and increase drag on the boat. The recent deepening of
Oars (as opposed to paddles) are essentially levers—but unlike a lever you might use to lift a boulder, where the fulcrum is close to the boulder and the long end of the lever is toward you, in an oar, the fulcrum is close to you and the long end of the lever extends into the water. In the former case, the energy necessary to move the long end of the lever a long distance is translated into a greater force over a short distance underneath the boulder. But in rowing, the goal is to move water as fast as possible over as long a distance as possible, so oars transfer a great force applied to the short end of the lever into a faster but less-forceful movement of the long end.
“No limits!” may be the official motto of the Canada Summer Games, but I have my own: “Don’t just spectate—cogitate!”
You’re welcome.
