Portland Plotter

A navigational tool used in marine chartwork to measure and plot courses, bearings, and distances on nautical charts.

The Portland Plotter is an essential instrument in the toolkit of any navigator, particularly in traditional maritime navigation. It is a flat, rectangular piece of transparent plastic, typically marked with a compass rose, parallel lines, and a protractor scale. The tool is designed to assist sailors in accurately plotting their position, determining a course to steer, or measuring bearings and distances on a nautical chart. Its transparency allows the user to see the chart details beneath it, while the markings provide the necessary references for precise navigation.

One of the key features of the Portland Plotter is its rotating compass rose, which enables the user to align the plotter with the chart’s meridians or parallels. This alignment ensures that the bearings or courses measured are true to the chart’s orientation. The parallel lines on the plotter are used to transfer a course or bearing from one part of the chart to another, maintaining accuracy over distances.

The tool is particularly valued for its simplicity and reliability, requiring no power source or electronic components. It is often used in conjunction with dividers to measure distances between points on the chart. While modern electronic navigation systems have become prevalent, the Portland Plotter remains a vital backup tool and a fundamental part of traditional seamanship training. Its use reinforces an understanding of chartwork principles and ensures navigators are prepared for situations where electronic systems may fail.