Canadian open water swimmer Jen Alexander, a former mathematics teacher, realized something really cool while swimming last week. “It has to do with measuring distance to shore using building heights,” explained Alexander who was the first swimmer to complete a double crossing of the Northumberland Strait (19 hours 17 minutes). “It works out especially well in Lake Ontario.”

In 2007, Alexander received the Diabetes Exercise and Sports Association’s “Athlete of the Year” award for her achievements as she swims attached to a waterproof insulin pump.

“Imagine this example. You take ruler, and hold it out at arm’s length. You then measure how big the CN Tower appears (in centimeters) from the water’s surface. You then divide 36 by that number, and that’s how far you are from the CN Tower in kilometers. Let’s say the CN Tower appears 3 cm tall. 36/3 = 12, so you are 12km from the CN Tower.”

Easy enough, but who has a ruler in the water?

Alexander has a solution.

“It can also be extended it to a trick a swimmer could do by using their fingers. Instead of taking a ruler, hold your arm out, and measure how tall the building is in finger widths. You can tell how far from the shore you are that way, too.”

Photo courtesy of Solo Swims.

Copyright © 2012 by Open Water Source