Navigation: Dead Reckoning

In navigation, dead reckoning is determining your current position based on your last known location. Because canoes and kayaks seldom leave sight of shore, you mainly use it during crossings, along featureless shorelines, in foggy conditions or to give you an estimated location between fixes. You can use the same technique to estimate your future position.

To do dead reckoning, start with a known location, such as a navigation fix, marked on your chart or map. From that point, advance a line along your known course a distance based on your speed and the time traveled using the formula shown below. Current or wind can affect your DR; during critical maneuvers you should account for these factors. Determining speed is based on experience. Before you find yourself in a situation that requires dead reckoning, figure out the speed you typically travel at.

Distance = Speed x Time

You should mark a new point at a set interval or each time you change your course or speed. Marking a point every hour makes the multiplication easy.

Let’s say that we’re circumnavigation Isle Royale on Lake Superior. It’s a typical foggy Lake Superior morning when we leave Siskiwit Bay. At 8 am, we’re able to fix our position just off the point of Fisherman’s Home Cove, and we mark that on the chart with a circle around a “X”. We know that we’ve been traveling at 3 knots, and today it feels like we’re still paddling that pace. We follow a heading of 244 magnetic. At 9am, we decide to mark our location on the map. Because we traveled for an hour at 3 knots, we know we traveled 3 nautical miles. We draw a line showing the distance on the map and mark it DR (for dead reckoning), write the time and write our heading and speed along the DR line. Use a partial circle to show your DR point.

To estimate a future position, use the same technique to extend your heading along a line.