Swimming Straight In The Open Water

Swimming Straight In The Open Water

Let’s say you are 1 kilometer from the next turn buoy. If you are capable of swimming straight, you have 1000 meters to swim.

But no one swims perfectly straight all the time, especially when there are lateral currents, waves or surface turbulence to account for. What happens when you make a 1° mistake in your navigation? How far are you be from the optimal straight-line tangent and the turn buoy? How far would you have to make up competing against a swimmer of similar speed who swam right on the rhumb line?

Using the Pythagorean Theorem Calculator, used for calculating the hypotenuse length of a right triangle, you can calculate your extra swimming distance here.

You would be 17 meters off the optimal line with a 1° diversion. If you are swimming at the average speed of a female Olympic 10km Marathon Swim athlete (assume 2 hours for the 10K), that navigational error is about a 12-second mistake. Not bad for an amateur swimmer doing a weekend swim or a local triathlon, but that same 12 seconds could be the difference between a gold medal and 10th place at the Olympic 10K Marathon Swim and an even greater distance on land once the triathletes hop on their bicycle.

But 1° diversion is frankly an excellent indicator of a high navigational IQ for a vast majority of people. 3-5° is more common. A 3° diversion equates to a 50-meter mistake over a 1000-meter distance.

Which, according to your opinion or perspective, is a good reason to have many buoys along an open water swim course – or not.

But as famed channel swimmer Forrest Nelson correctly points out, “With each sighting, new information becomes available to the swimmer, enabling the swimmer to continuously plot a better course. In fact, theoretically, an open water swimmer could always be navigating “1° off course” for the entire kilometer, with frequent course corrections, and still hit the buoy just a fraction of a second off the perfect navigator.”



Information courtesy of Forrest Nelson, an MIT graduate.

Copyright © 2011 by Open Water Source