Have you ever noticed how boats look when they're built more for speed than for carrying cargo? The classic cargo-carrying vessel is the barge. It's just as broad in the front as it is in the middle, the better to maximize cargo capacity. But it doesn't matter how powerful a tug is pushing it, the barge will never move at more than a crawl, even when moving downriver empty.
The classic built-for-speed vessel is the racing shell because its human cargo is also its engine. Even though it has only an 8- human-power engine, compared with the thousands of horsepower driving the tug, the crew shell really flies across the water. Now what about that shell's design? Not only is it needle-like from stem to stern, but it has an awful lot of length both in front and back of where the crew sits. There's a lesson in that for swimmers.
In the 1830s and 1840s, there was a fever among clipper ship owners to break the speed record for various ocean crossings. Because they had only sail power to rely on and couldn't simply install a bigger engine, the the only way to gain speed was to change boat design. A naval architect named W. Froude tested various vessel shapes in a water tank to figure out what ratios of length, width and draft would produce the fastest boat.
Froude's critical discovery was that, all other things being equal, the best way to reduce drag was to design the boat to be longer at the water line. To this day, "Froude numbers" are used in boat design, and if you look at any boat-built-to-go-fast, from the racing shell to an America's Cup yacht, they all have the same long, sleek shape.
What's the implication for the vessel that carries you up and down the pool? Many swimmers assume that the best way to go faster is to make the engine (muscles and CV system) bigger. They hit the weight room, pull with paddles or do more yardage (to increase the engine's available fuel--heartbeats and calories). But any potential increase in engine power will always be puny in comparison to the amount of drag faced.
So vessel design that reduces drag will clearly have a far greater payoff. Froude told us that drag and the power required to overcome it are greatly reduced when you increase the length of the vessel. If you put a 12-foot and a 16-foot canoe in the pool side by side and push both away from the wall with equal force, the 16- footer will always go farther, faster and truer. Okay, I understand that if my body was longer I'd travel through the water faster and further on every stroke. But I'll never be taller than 6-feet, so how does that apply to me?
Well, when I extend an arm overhead I'm nearly 9-feet long from my fingertips to my toes. And Froude's research showed that a 9-foot vessel would travel nearly 25% faster than a 6-foot vessel. There's a simple experiment to test that. Push off the wall as hard as you can with your arms at your sides (the 6-foot position) and glide as far as you can. Then go back and do it again, but with your arms streamlined overhead (the 9-foot position). You'll glide a lot farther.
Conclusion: One way to swim faster with no more effort is to keep your body as long as possible for as long as possible during each stroke cycle. There are three ways to do that:
In the final analysis, there's no advantage to stroking faster if it reduces your reach. Keeping an arm outstretched in front of the body for just a bit longer during each stroke cycle allows your "vessel" to be longer for more of each stroke cycle and hugely reduces the drag on your body. You should feel a very slight overlap (or catchup) in your strokes. Too much overlap will mess up your stroke rhythm. Just a split-second longer can make a difference. You'll travel farther and faster with no more effort on every stroke. Happy laps!