This article is an excerpt from NauticEd’s online Skipper Large Keelboats Course, a comprehensive online sailing course for beginner to intermediate sailors to learn how to sail large sailboats 26 ft (8m) and above. The Skipper Large Keelboats course is part of the Skipper Course Bundle of online courses, also teaching you how to master maneuvering under power and docking!

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We begin with a phenomenon called magnetism. This phenomenon was known thousands of years before electricity. Magnetism was discovered in a section of Asia Minor known as Magnesia where the Greeks observed that strange metallic-like rocks would attract bits of iron. This was the beginning discovery of “magnets”. These stones with their unseen power were also called lodestones by early explorers and sailors.

Magnetic Field

As more became known about these magnets, it was discovered that they possessed two distinct focal areas, that today we call poles. By convention, one pole is called the North Pole and the other the South Pole. The unseen force between them is called magnetism.

When magnets are spun (rotated) through a magnetic field they will generate electricity. The power to spin these magnets comes from a variety of sources, such as falling water in huge dams, geothermal steam, steam generated by other means such as burning coal and nuclear fuel, and in particular for boats – diesel engines and wind turbines.

2.2.1 Earth’s Magnetic Field

The pervasive magnetic field surrounding magnets flows in a complete loop around the poles from north to south.

Interestingly enough, the earth itself is one huge magnet with a relatively strong magnetic force field surrounding it. 

earths magnetic field

When a magnet is allowed to freely rotate on a pivot, it becomes a compass. One end will always point to the Earth’s North Pole and the other to the South Pole. Of note, these magnetic compasses do not use any source of additional power. For a long time, it was thought that magnetism was a key to creating perpetual motion.  But that was never to be found true – of course!

A Compass The needle of a compass is made from lodestone which is thought to be created in an iron-rich stone called magnetite.  The high magnetic field generated from lighting strikes close to magnetite rocks will permanently magnetize it and thus transform it into a lodestone. Lodestones named from Old English – literally “course stones”, are the only occurring naturally magnetized material on earth and are attributed to being discovered by a Greek Mathematician in 600 BC. The last piece of trivia around this is that the word magnet probably comes from the place Magnesia now in Turkey where lodestones were originally found.

This naturally occurring magnetism in rock particles led to the development of a compass and was the primary navigation aid for ancient mariners and is still very much in use today. This simple device will point in the directions we call the North and South magnetic poles on the Earth. Unfortunately, these magnetic poles are not the same as the geographic poles. In the Navigation Module, you will learn how to compensate for this difference. Compasses are affected by close-by magnetic fields. Therefore, whenever using a compass make sure your compass is only experiencing the magnetic field from the earth.

Magnets are also used in electric motors, alternators, and generators that all exist on boats today. Without magnets and magnetic fields, the world would be a very different place.

large hydro generator
A Large Hydroelectric Generator.

small belt driven generator
A Small Engine Mounted Belt Driven Generator


Boat Stand Alone Generator

A Typical Generator in Boats 40 ft or Greater

You can learn more in the Skipper Course....

Knowledge and theory for longer distances and overnight sailing in diverse conditions. The Skipper Course is a comprehensive online sailing course for beginner to intermediate sailors wanting to learn how to sail larger sailboats 26ft to 56ft. Or upgrade to the Skipper Course Bundle of online courses to also master maneuvering under power and docking!

Source: Skipper
Topic: Boat Electrical Systems
Authors: Grant Headifen, NauticEd Global Director of Education
NauticEd is a fully recognized education and certification platform for sailing students combining online and on-the-water real instruction (and now VR). NauticEd offers +24 online courses, a free sailor's toolkit that includes 2 free courses, and six ranks of certification – all integrated into NauticEd’s proprietary platform. The USCG and NASBLA recognize NauticEd as having met the established American National Standards.