Boat Electrics

Boat Electrics 101 - Safe & Reliable DC Systems

6 Modules 48 Lessons Beginner

About this course

Welcome to Boat Electrics 101, the first online course from

Boat Electrics 101 will increase both your safety and your self-reliance on the water. The modules in this course will help you to understand your electrical system, and provide you with the necessary knowledge to fix it, extend it, or even completely rewire your boat in a professional way.

This course is the result of a joint effort of the three founders of BoatHowTo: Jan Athenstädt, Michael Herrmann and Nigel Calder. You will find detailed information about us towards the end of this page.

Course Goal

Our goal for this course is to provide sufficient information for even beginners to develop a comprehensive understanding of the DC system on their boats. This course should enable everyone to install and fix things on their own, or at least have the ability to spot potential points of failure in a system. 

This is an important part of seamanship these days, and more important than ever. And it applies not just to used boats, because in our experience even boats that come straight from the boat builder sometimes have electrical systems that are badly installed, and on occasion potentially dangerous.

Even boaters who already know the basics will benefit from the later lessons where details for safe and reliable installations are discussed along with systems design.

We believe that if you master everything we cover here in this course, you will quite often be able to do a better job working on your electrics than many so-called "marine electricians".

If you do it: Do it right!

That is our motto for this course. And in our opinion, the best way to do things right is to understand why you are doing them. 

That's why we not only want to tell you what to do, but we also want you to understand why and how and enable you to make your own informed decisions

Some of this content will be difficult for novices and you will need a certain commitment to learning. Unfortunately, there is just no way around this and there are no shortcuts with boat electrical systems.

Whether it comes to choosing new equipment, installing equipment, or troubleshooting your existing installation: The same basic knowledge is necessary for everything from a minor rewiring job to a complete rewiring of a boat, or when starting from scratch with a new build.

No matter how simple the circuit, it is either correctly designed and installed or it will be prone to trouble and potentially unsafe .


If the content becomes overwhelming, it is an indication that you should look for professional help. Don't try to muddle through on your own if you are not sure what you are doing.

Even if you are only installing simple circuits, you need the base knowledge we teach in the following modules. Without this you will not be able to do a proper job when it comes to sizing cables, determining what overcurrent protection devices to use, where to put them, and so on.

Meet the  Team

Dr.  Jan C. Athenstädt

Your Teacher

Jan runs a German online magazine for boatowners and an online shop for boat electrics.He has a PhD in Computer Science.

Jan is the youngster in the BOATHOWTO team. During his studies of computer science in Germany and the US, he has worked as crew on various tall ships before moving aboard his own boat.He started teaching people how to install and maintain technical systems on their boat through his online magazine KlabauterKiste.He later started an online shop for boat electric supplies which he runs from his boat while sailing the Med.Jan takes care of the technical side of BOATHOWTO and will guide you through most of the video lessons.

Click here to learn more about Jan's story...

Nigel Calder

Expert on ABYC Standards

Author of the famous  Boatowner’s Mechanical and Electrical Manual , often referred to as the "bible for boatowners"

Nigel is a full-time sailing writer, with a focus on marine technical systems. He is often referred to as THE guru when it comes to mechanical and electrical systems on boats.His books are widely acclaimed by both boaters and professionals in the field. His most famous book, the Boatowner’s Mechanical and Electrical Manual has sold over 300,000 copies and has a staggering 4,8 stars from 596 ratings on Amazon.Besides writing books, Nigel is a long-time member of the American Boat and Yacht Council (ABYC) electrical Project Technical Committee (PTC) which writes the standards for recreational boat systems in the USA, and has also been involved in European standards development.

Click here to learn more about Nigel's story...

Michael Herrmann

Expert on ISO Standards

Author of several books about technical equipment on boats.His book on electrical systems "Elektrik auf Yachten" is considered THE reference for technical information in the German language.

Michael belongs to the rare kind of people who combine a vast theoretical knowledge with the ability to apply this to the practical world.Besides having written seven books, he has published over 500 articles in technical magazines, mainly on the topics of boat electrics and mechanics.Since 2007, Michael has been a member of the German Boat Builders Association committee on electrics, and a member of ISO TC188 which establishes standards for small craft.His latest activity in the ISO was contributing to the merger of the two basic standards for DC and AC electrical systems on recreational craft - ISO 10133 and 13297.

Click here to learn more about Michael's story...

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Course Structure

3 Lessons


About Boat Electrics 101

A quick welcome and introduction of your teachers and a few words on who this course is for and what to expect.

Course Structure & Overview

Get an overview on the contents of this course and the underlying standards.

Safety Precautions

In this lesson we will cover some dangers and necessary safety precautions to keep in mind before working on your system.

8 Lessons


Get to know the basics of electricity and learn about Volts, Amps, Ohms and how they relate to each other.

What is electricity?

What is electricity and what happens when a current flows? We take a quick look at the behavior of electrons inside metallic conductors.


Learn all you need to know about voltage, the equivalent to pressure in electrical systems.


The current (given in Amperes) is the amount of charge that moves through a conductor.

Resistance and Resistors

In this lesson, you will learn how resistors reduce the general movement of electrons and how resistance affects the flow of electrons in conductors.

Ohm’s Law

Ohm's law allows you to calculate how resistance affects voltage given a certain current and vice versa.


Power the product of voltage and current. With two examples you will learn how to calculate the power draw of an appliance.

Energy, Consumption and Capacity

In this lesson, you will learn how the power supplied over time serves a measurement for energy and how this can be used to describe the capacity of batteries.


A quick recap on everything we have learned so far.

9 Lessons

Electrical Components and Circuit diagrams

Get to know the most common components of a boat's electrical system and learn how they can be represented in a circuit diagram.

The Idea Behind a Circuit Diagram

Learn why it is important to be able to read and draw circuit diagrams.

Wires and Conductors

In this lesson you learn the symbols for wires and wire connections.

Circuit Ground

What is ground/earth and how is it represented in circuit diagrams?

Switches, Buttons and Relays

Get to know the basic symbols for switches and buttons and learn how relays and solenoids work.

Resistors and Shunts

Get to know the symbols for resistors and learn about the most common type of resistor on board: the shunt.

Fuses and Circuit Breakers

How are fuses and circuit breakers represented in circuit diagrams?

Coils and Transformers

Coils mostly occur on boats within transformers. Here you will learn about their basic function and how to represent them.

Lamps, LEDs, Diodes, etc.

In this lesson you will get to know a few more symbols for common components in a boat's electrical system.

Basic Circuits

In the final lesson of the module, you will learn how the components in boat electrics are connected in parallel and in series and how this affects battery capacity and voltage.

9 Lessons

Cable Selection and Installation

In this module, you will learn how to choose the right type and size of cable and how to properly install it. This is crucial knowledge for anyone planning any modification on their boat's electrical system.

Cable Construction

Learn about different types of cables and which ones are suitable for use on boats.

Colors and Labeling

Learn what cable colors you can use for what purpose and how to properly label your wiring.

Sizing Cables

Learn how to choose the proper size for a cable with respect to ampacity and voltage drop.

Terminals and Terminal Installation

It is crucial for the system's safety to establish proper connections. In this lesson you will learn how to install terminals in a professional manner.

Making the Connection

Proper connections of terminals to bus bars and consumers are vital. Here you learn what makes a professional connection.

Overcurrent Protection (OCP)

In order to prevent fires due to overcurrents and short circuits, protective measures are absolutely crucial. In this lesson you will learn how to choose fuses and circuit breakers and where to install them.

Cable Installation

Learn the proper way to install cables in order to protect them from chafing and physical stress

Case Study: High Output Alternators

In this lesson we will apply what we have learned in this module to the special case of high output alternators. As we will see, there are quite a lot of things to consider.

Bonus: More Examples

Here we show a few more examples of good or bad installations and also what happens in case of a short circuit if no adequate OCP is installed.

11 Lessons


In this module we cover all you need to know about lead acid batteries.


Get an overview on what to expect in this important module.

Battery Safety

Even though they operate at relatively low voltages, there are significant dangers when dealing with batteries. In this lesson we cover the required safety measures.

Lead-Acid Battery Chemistry

In this lesson you will get an overview on the chemistry inside a battery and how lead acid batteries work.

Battery Construction

Here we go more into the details of the internal construction and discuss the differences between cranking and deep cycle batteries.

Battery Types

Now it's time to look at different types of lead acid batteries, such as wet cell, AGM, gel-cell and some new innovations.

Battery Efficiency

Learn about the crucial difference between amp-hour and watt-hour efficiency and how to evaluate batteries based on this.

Battery Ratings

What do the common ratings found batteries (nominal voltage, nominal capacity and cold cranking amp) mean?

Battery Failure Modes

In this lesson you will learn what the most common reasons for battery failure or reduced lifespan are and how to avoid them.

Series and Parallel Batteries

Learn how to maximize battery life when installing batteries in serial or parallel.

Sizing Battery Banks

This lesson will help you decide how much battery capacity you really need for reliable operation and optimal battery lifespan.

Lead-Acid Battery Installation and Maintenance

Learn how to properly install your battery bank and how to maintain it in order to optimize its performance.

8 Lessons

Charging Systems

In this module we cover in detail all you need to know about charging batteries. Topics include charging profiles, charging systems, charging circuits and systems monitoring.

Failure Modes Revisited and Expanded

Learn about the most common failure modes with lead acid batteries so mistakes can be avoided.

The Water Tank Analogy

Through the analogy of a water tank with semi-permeable membranes we explain why it takes a long time to completely top off a lead acid battery.

Charge Profiles

Learn what an IUoU profile is and how the bulk, absorption and float phases increase battery life.

Fast Charge and State of Charge (SOC)

Learn strategies to reduce charging times and engine hours while at the same time increasing your battery's lifespan.

Charging Devices

Learn what to look for when choosing a battery charger, an alternator or when planning on installing renewable energy sources.

Charging Circuits

Learn about different ways to charge multiple battery banks from a single power source.

Systems Monitoring

Learn about the importance (and challenges) of proper battery monitoring.


A quick recap on what we have learned so far in this module.