Section 6

Getting Your Bearings

6.1

Bearings

  
The bearing of the lighthouse from the boat is 170° M. This is a magnetic bearing that will have to be corrected for local variation to convert it to true.
   

A bearing is the direction of one object from another. The direction of a bearing is expressed in degrees from 0° to 360°. An object that is due east of a mariner would have a bearing of 090°. As with courses and headings, bearings are written using three digits, including zeros. An object due south would bear 180°, one southwest, 225° and one three degrees east of north, 003°.

 

Objects of Bearings

Navigators use bearings on visible, charted objects or land features to determine the boat's position. These include aids to navigation, structures on land, and coastlines or prominent points of land.

It's worth the effort to learn to take bearings quickly, accurately and under all conditions.

Hand-held compasses are often used to find the bearing of an object. The resulting magnetic bearing has to be corrected to true in just the same way as a magnetic course is corrected.

Bearings and the Steering Compass

A boat's steering compass can be used for taking a bearing by pointing the boat at the object and reading the compass heading. A bearing taken with the steering compass needs to be corrected for deviation as well as variation. The deviation of the bearing is the same deviation as the boat's heading.

On many steering compasses - particularly binnacle-mounted models - you can sight over the card to get the bearing of an object without pointing the boat towards it. Because deviation depends on the boat's heading, the deviation is that of the boat's heading, not of the direction of the bearing. This is an important point to remember and one that even experienced navigators sometimes overlook.

Bearings and the Hand-held Compass

You will be able to take a bearing free from deviation provided you remove a hand-held compass from magnetic influences on the boat. You then need only to correct for local variation to get a true bearing. Most hand-held compasses are designed specifically for taking bearings.

A hand-held compass displays a bearing of 170°M, a magnetic bearing, to the lighthouse.
A hand-held compass is uncomplicated to use, although it takes practice to get an accurate reading from an unsteady deck. The compass is held at arm's length or to the eye, depending on its type. It's pointed at the charted object and the magnetic bearing is read off a rotating compass card behind the lubber's line. There are electronic versions of the hand-held compass available as well as binoculars with integrated compasses.

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