Navigation: Aiming Off

When you’re paddling to a destination located somewhere along a nondescript shoreline, it’s easy to miss your target even if you took an exact bearing. There are lots of reasons why this might happen, some of those reasons include wind or current pushing you off course, lack of attention, slight inaccuracy in your compass reading or maybe magnetic deviation. But, the truth is that it’s hard to end up at an exact location without a visual clue. In situations like this, use a technique called aiming off to make sure you end up at your desired destination.

How to Aim Off

To aim off, you deliberately set a course off to one side of your destination. By setting a course off to one side, you know that when you hit the shore, you just need to turn towards your destination and eventually you’ll find it. When you don’t aim off, if you miss your destination you won’t know which way to turn to find it. Because compass errors and drift are common and usually a couple of degrees, you want to aim off enough to compensate for any error. There’s no standard amount of degrees to aim off, because there are too many variables. For example, on a calm day, you may only need a couple of degrees, but on a windy day with strong current, you may need 10 or more. Over time with practice, you’ll gain a feel for how much you need to aim off. At first, aim further off than you think you need.

When setting your new course consider wind and current. If you aim upwind or up-current of your destination, when you turn towards it, the current or wind helps push you along.

Calculating Distance from Destination

When aiming off, you’ll end up some distance away from your destination. To calculate the distance, you could use the formula listed below, or you could roughly estimate it with this simple rule: over a mile, for every degree you aim off, you’ll end up 92 feet away from your destination. For example, if you aim off 5 degrees and paddle 2 miles, you’ll end up 920 feet away (92*5*2=920).

Distance from destination = tan(degrees off) * distance to destination

Aiming Off Example

Let’s say we’re visiting one of the two dozen permanent residents on North Bass Island on Lake Erie, and we decide that we want to head over to Pelee Island to visit Canada. We’ll need to check in with customs, so we need to land at the west dock which has a customs office.

Our crossing is about 7 miles. Our course bearing (red line) from the southeast corner of North Bass to the west dock on Pelee is 57 degrees (64 degrees magnetic). There’s a 10 knot south wind blowing, so we decide to aim off by 7 degrees to the south. We set our course bearing (green line) to 64 degrees (71 degrees magnetic).

Without any drift, we’ll end up about 8/10th of a mile or 15 football fields south of our destination (92* 7 degrees * 7 miles = 4508 feet). With a 10 knot wind, we’ll probably experience some drift to the north, so there’s a good chance that unless we compensate we’ll hit the shore closer to the west dock than we expect.

After we reach the shore, we turn north and paddle the shoreline to the west dock and enjoy our visit to Canada.