Navigation and Seamanship

2.1.1. Introduction

The magnetic compass is the oldest instrument for navigation and has been an essential tool for navigators at sea to find the directions. The compass shows the way to the ships to steer a selected course. By taking bearings of visible objects with a compass, the navigator is also able to fix a ship's position on a chart. The earliest compasses probably consisted of an elongated piece of lodestone or iron ore having magnetic properties, placed on a wood chip and floated in a bowl of water. Because of the difficulty at sea in using a needle floating freely in an open bowl of water, the next development was that of using a pivot at the center of a dry bowl. Not for some centuries was the liquid put back in, this time in an enclosed chamber, as now is the case in modern magnetic compasses.

Initially, a compass was used only to indicate north, but soon the concept of marking other directions around the rim of the bowl was introduced. In olden days, compass cards were marked out not in degrees, but in points. There were 32 points, matching the directions of winds which sailors would be familiar with at sea. The four main points – North, South, East and West – are called the cardinal points. . Next are the inter-cardinal directions: NE, SE, SW, and NW. Still finer subdivisions are the combination directions: NNE, ENE, ESE, etc.; and the by-points: N X E, NNE X N, NNE X E, etc. This system results in a complete circle divided into 32 points ( 1 point = 11 ¼ °) and there are half-points and quarter points. The point system was widely used until relatively modern times, but is now obsolete except for some minor use on sailing craft.

The magnetic compass still retains its importance, despite the invention of the gyrocompass. While the latter is an extremely accurate instrument, it is highly complex, dependent on an electrical power supply, and subject to mechanical damage. The magnetic compass, on the other hand, is entirely self-contained, simple, comparatively rugged, and not easily damaged.