Plotting the course

To determine the ship’s course, nautical charts and compass were used as well as the hand log that measured its speed.
The course of the ship was plotted on the nautical chart and distances were measured in nautical miles. Galaxidian sailors used charts of various origins but all with the Mercator projection of the spherical earth on the plane surface of the chart. With these nautical charts accurate calculations could be made for the journey.

The compass was an essential instrument for each ship, as it is also today. The use of the magnetic compass spread throughout Europe in the 12th century, but it seems that it was used in China much earlier. It contributed decisively to the spread of European civilization to the rest of the world. To begin with, it was a magnetic needle mounted on a wooden pin that floated in water in a bowl. From the 13th century a card was added with markings of the wind directions, which is characteristic of the nautical compass since then. These cards have radial markings for a total of 32 points, and the north point is usually marked by a fleur-de-lis.

The compass allowed the sailors to determine their course even when the cloudy sky hid the sun during the day or the pole star at night. Also, early on clever sailors were able to deduce roughly the longitude with the help of the compass from the angle between the true geographic north determined by the pole star and the magnetic north shown by the compass. This angle changes as one travels westward or eastward.

Galaxidian sailing ships were equipped with nautical compasses, which then were mounted in wooden boxes with a glass cover and placed on the bridge of the ship.