The electrical system on a sailing boat

The electrical system is one of the most important systems on a boat and as we use more and more electrical equipment on board, the need for electricity increases. In these articles, I have the ambition to write about electrical systems, so that most people who are interested can understand how the system works and benefit from it onboard their boat.


Although I think I have good knowledge of electricity and electrical systems from my education as an electrical engineer, I missed a lot of practical knowledge about how the electrical system on a boat works. It became obvious to me when we got our first long-distance sailing boat over 20 years ago. Then we switched from a Maxi 77 with an outboard engine, to a 40-foot Långedrag 401 built of steel with a much more complex electrical system.

Since then, I have learned a lot about electrical systems on board, partly because I wanted to add equipment to the systems, for example, an isolation transformer, battery monitoring. But also because parts have stopped working and I have been forced to troubleshoot and fix the faults myself.

As usual, there is a lot of information on this topic on the internet, but often only about a sub-area or someone has described how they changed their electrical system. For me, it has meant that I have had to put together information from several different sources to arrive at how something works or should work, I have also bought books on the subject to learn more.

In these articles, I hope to be able to give you the whole picture in one place.

A modern long-distance sailing boat has a much more complex electrical system than a house. The boat’s system also contains generation and storage of electricity and has both direct voltage and alternating voltage to handle. You also want the system to be fault-tolerant because you are sometimes far from someone who can help fix it when something stops working and then at least I want to understand what needs to be fixed and preferably also why it happened.

One thing I have learned over the years as owner of sailing boats is that sooner or later there will be problems with the electrical system, even if the boat is new.

What I plan to write about

Since it is a fairly extensive subject area, I have divided the series of articles into these areas.

  • Part 1, Fundamentals of electrical systems
    In this article you can read about the basics of electricity. Direct current (DC), alternating current (AC), 1-phase, 3-phase, electrical current and resistance. In electrical engineering, there is a central formula, Ohm’s law, which I explain how it works. With its help, you can calculate electrical current, voltage, and resistance. I also go through the concepts of power and energy.
    There is also a practical part about how to use a so-called multimeter (a measuring instrument) to measure voltage, resistance and current.
  • Part 2, Overview of the electrical system on board
    Here I thought I would make a general description of an electrical system intended for a newer sailing boat around 40-60 feet with shore power connection, power plant, solar panels, wind power, several battery banks and the possibility to connect equipment that uses 12V, 24V or 230V. I also write a bit about fault tolerance and spare parts.
  • Part 3, Electrical drawing and reality
    In this article, I go through how an electrical drawing is built and what information is in it. What do the symbols on the electrical drawing mean and what does the corresponding equipment look like in reality?
  • Part 4, Cables and fuses
    This article is a continuation of the article on electrical drawing, but it contains more practical information on sizing, marking and the use of colors on cables. You can also read about different types of fuses and where to place these and why.
  • Part 5, Batteries and Charging
    Pros and cons of one or more battery banks? How should they be charged? What properties have different battery types and where are they suitable for use. How to connect one or more battery banks in the electrical system so that they are charged in a good way without the charge shortening the life of the batteries unnecessarily.
  • Part 6, shore power connection
    What should I think about when the boat is connected to shore power in a marina or when it is stored on land? What components are needed and how are they connected to the rest of the electrical system on board?
  • Part 7, Generator
    Pros and cons of a generator? What should you think about if you are going to get a new generator or replace the old one? How is it connected to the rest of the electrical system on board?
  • Part 8, Sun, wind and water
    How much power and energy do you actually get from the natural energy sources you have access to? How to connect solar panels, wind turbine or water generator to charge the boat’s batteries in a good way?
  • Part 9, Inverter
    What are the pros and cons of an inverter? What to think about if you are going to install an inverter and how is it connected to the rest of the electrical system.
  • Part 10, Corrosion problems with electricity on board
    Improper installation of the electrical system can cause corrosion of the engine, propeller, bushings and other metallic equipment in contact with water or electrical systems. In this section, I write about why corrosion occurs, and what can be done to counteract it.
  • Part 11, Lightning protection
    Can you do anything to protect yourself from the effects of a lightning strike near the boat or even worse, if you get a direct hit in the boat? I will try to compile advice and techniques available to reduce the effects of lightning and how they affect the electrical system on board.

What the articles will not contain

The article series will not describe how different components should be connected in detail or evaluate components of different brands against each other. Instead, I hope that the knowledge you gain through these articles will allow you to decide for yourself which brand or component to choose.

Onboard a boat there are also other systems that use electricity. Eg lighting systems, navigation systems, autopilot, fridge and freezer, computer networks, systems for communication with the outside world, systems for generating and distributing fresh water on board, fuel systems for engines and power plants. Maybe there are even media systems for playing music and movies.

Although all of these systems use electricity and are connected to the electrical system, I have no plans to write about them in this series of articles. From the perspective of the electricity system, they are all consumers of some kind.

This series of articles begins where you connect shore power, produce electricity, store electricity, and end at the boat’s electrical central(s) where the consumers’ cables are connected. Maybe something to write about in the future.

Concluding remarks

With this article, I hope you have become more curious to learn more about electrical systems. I also hope to get your feedback on this topic so that I can shape the content according to what needs really exist.

  • Want to read more about the subject?
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What do you think, can this be something to write about?

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