Check your Compass using the CompassAdjuster Pelorus

First download the CompassAdjuster Pelorus card to make a pelorus using a CD and CD case. You will need to print and glue the card face to a CD disc. (Check the printer has not distorted the compass card.) The final step is to locate the centre of the CD with a sighting peg. Alternatively a printed disc can be purchased through Compass Adjuster. To buy a printed disc, send a message to organise payment and delivery.

Conventional peloruses are used to determine a bearing of an object with the knowledge of the vessel’s heading. The CompassAdjuster Pelorus is used to determine the vessel’s heading with the knowledge of a bearing.

The CompassAdjuster Pelorus is graduated counter-clockwise to allow for expedient determination of the vessel’s heading.

Checking your Compass using a known distant bearing.  

1. align the CompassAdjuster Pelorus with the vessel’s fore & aft axis. This can be done aligning the case with a fore & aft or athwartship structure such as a hatch or heading the vessel directly at the sun and align the case so the shadow from the sighting peg falls on the reciprocal lubberline.

2. establish the magnetic bearing of a distant object, either from the chart or by hand bearing compass.

3. rotate the CompassAdjuster Pelorus card so that the value of the distant object’s bearing is on the lubberline.

4. observe the distant object through the sighting peg and note the vessel’s heading off the CompassAdjuster pelorus card.

Checking your compass using the sun’s shadow

1. place the CompassAdjuster pelorus in a position it will be in sunlight for most of a vessel rotation and ensure the  pelorus is level and the sight peg perpendicular..

2. place the vessel on a know magnetic heading, be it on a set of leads or towards a distant object of known bearing.

3. rotate the card on the pelorus until the shadow falls on the value of the vessel’s magnetic heading

4. the vessel’s heading will now be indicated by the shadow of the sighting peg.

When the sun is low, its change of bearing is slow. However, if you are slow in checking your compass, you can always resume a known heading and reset the card. If unable to establish a known magnetic heading, set up the pelorus on a compass heading.

(CompassAdjuster.com.au is working on the ability for you to download the sun’s magnetic bearing for a given location, time and time increments. In the meantime, the following two links may be of help to find the sun's true bearing and magnetic values for your location. With knowledge of the sun's magnetic bearing, simply rotate the card until the sun’s bearing for the time is on the reciprocal lubberline and the vessel’s magnetic heading will be indicated by the shadow of the sighting peg.)