Science Matters takes you inside the Physics of Crew. Since making an appearance in the first modern Olympic games in 1896, the sport of rowing has been notorious for its difficulty, competitiveness, and high level of precision. Also known as Crew, this sport has high school, college, adult, as well as national level teams that compete in races called regattas all over the world. Boats race side by side for a short 2000 meter distance or a longer 5000 meter distance as a time trial at speeds reaching 15 miles per hour.
So how does it work? And where does Physics come in?
The sleek styles of boats used in this sport are called “shells” and have between one and eight rowers, as well as in some cases a coxswain who uses voice commands to direct the rowers and keep them in time. The rowing stroke has two distinct parts. The first part is called the “drive.” This is where the oar is in the water and the rower is pulling on it to generate speed. The second part of the stroke is called the “recovery,” when the rower takes the oar out of the water and uses his or her sliding seat to move back up for another drive.
There are two elements to the relative motion of the rowers body in relation to the hull. The first is the rowers body, which moves initially when the rower pushes off with compressed legs to pull the oar through the water. The second part is the rowers’ torso, which swings back to fully pull the oar into the chest and then swings back over again as the rower moves up the slide on the recovery.
Two opposing forces determine the speed of the boat: drag from the water and thrust from the rowers muscles, namely their thighs. The drag is reduced by the shell’s streamlined design, but rowers must work to counteract the forces of drag during the recovery where they are not actively moving the boat through the water. In order to do this, first think of the boat and rower as one unit instead of two. This one unit has a velocity, or speed, which combines the velocities of the rower and the boat.
To keep the boat moving at roughly the same speed throughout the duration of the rowing cycle, the rower compensates by moving faster towards the bow during the drive, and then slows down the way up to the stern to take another stroke. In this way the velocities average out to combat drag.
Different kinds of shells have different numbers of rowers. Contrary to what you might think, adding a rower does not double your speed. While two rowers does have double the power and velocity of one, this doesn’t take into account for the ratio between power and drag, which differs from shell type to shell type.
In order to figure out what this ratio is, follow this equation:
Drag= number of rowers2/3 X velocity2
If you plug in 8, for 8 rowers, you find that the power to drag ratio comes out to be roughly 7, less drag per person than if a rower was in a shell by themselves. In addition to the lower drag per rower ratio, the greater the number of rowers the more they can work together on the recovery to conserve momentum. Another important factor is that shells of 4 and 8 rowers have coxswains which help them stay together and coordinate their movements for more efficient motions.
Check out this video of the Hickory Rowing Club from Chesapeake Virginia! As you’re watching, watch how the rowers move and think about the physics of how it all works, as well as the beautiful sunrise.
Article by: Margaret Carmel, an intern with Science Matters and a crew member. Margaret is a Virginia Commonwealth University student studying Broadcast Journalism, Middle Eastern Studies, International Social Justice, and Global Education.