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Preface and Contents

This book is about the theory and simple practice of electricity and electronics on boats. Not ships - though the theory is of course the same, as it is for anywhere electricity is used - car, plane, spaceship - but smaller vessels.

The book is for anyone who wants to understand how electricity and electronics works - in so far that is possible, and to the extent that I can help!

Humans are more and more dependent on technology, in every area of life. The last few decades of the 20th century have brought an unprecedented proliferation of electronic gadgets into many fields where previously and for hundreds of years, mechanical gadgets, some mathematics (in a simplified form) and simple adherence to some pre-prepared method had served people well.

An example: the 'Ready Reckoner' (available in many different forms) was a book of pre-calculated solutions to prepared problems - giving a reasonably simple way of dealing with things like:

'If each item costs 12.35 units, and there are 120 items in a box, and there is 10% discount for quantities over 3 boxes - but 15% for 10 boxes up - and my overdraft costs me 4% pa, and my markup is 33%, what should I sell them for and how many should I buy?'

Nowadays of course a pocket calculator (or its larger relative, a spreadsheet on a PC) would be used to get the answer.

Another example: in 1970 a yachtsmen might well have had an (electronic) depth sounder, and if it was a racing boat, there might have been a knot meter attached to the Walker log. But for position finding on passage, it would be a question of getting the sextant and the sight reduction tables out, and getting down to it.

In current practice, there will be a GPS (navigation satellite) receiver clocking out the course, waypoints, ground track, speed over the ground - plus the rest - and it may well be linked to a chart plotter to show your position. I am not suggesting that there is anything wrong with this. I've heard many people suggest that this trend indicates that people are just using the equipment without understanding what they are doing - but this was just as true of the previous technology. The whole point is to be able to use it without having to calculate everything manually every time.

There is, however, one big difference. If you dropped your Ready Reckoner in a bucket of seawater, it would work just fine once it dried out. If you dropped the sextant, there was some chance of fixing it. Try this with a GPS receiver. Have you ever looked at the electronics on your boat and asked yourself, 'how does it work? Could I fix it if it went wrong?'

If you have, then you are in the right place. This book is Electricity and Electronics for Boats: How it Works. Assuming you are of moderate intelligence and prepared to persist, you can quickly grasp all the basics you need to be able to understand - in principle - every piece of electronic or electrical equipment on your boat. Also, of course, this applies to your home, your car, the Space Shuttle - the electronics and electrics does not really vary all that much. Here, though, the emphasis is on small craft - boats of less than, say, 25 metres or so, and the examples, applications and problems are drawn from that field.

So: there we are. Shall we get started? But first you must read this disclaimer; I don't in any way want to frighten you away from electricity, but nor do I want to lose any readers to carelessness! You might also want to look at the Copyright Notice. Or, of course, find out how and why   Open in popup window this book was written.


  1. Please first read this warning and disclaimer
  2. Atom and electrons
  3. Conductors and resistance
  4. A little maths

Errors and Corrections

This work is offered in the hope that it may be useful but without any form of warranty as to its correctness. It is you, the reader's, responsibility to check any and all information that is presented here for its correctness. As far as I know it is correct, but errors always sneak in to any work, and it is probable that there are some errors here that I have not detected; even scientific claims often are modified in the light of newer theories. Therefore, please notify me of any errors or corrections, which I will implement if I agree and am convinced!







The author disclaims in totality any and all responsibility or liability for the accuracy in, or use that is made of, the information in this work. Before working on any electrical equipment, it is ESSENTIAL that it is isolated from any potentially hazardous voltage or current. Learning to work with electricity requires that you commence with ALL REASONABLE PRECAUTIONS in place. IF YOU ARE IN ANY DOUBT as to what you are doing, do not touch any equipment without supervision from an experienced and/or qualified person. Even if you are certain that you are correct, double check. ALWAYS test circuitry for dangerous voltages or currents using test equipment with suitable INSULATED PROBES. Suitable equipment might be a voltmeter, ammeter or general voltage indicator. TAKE ESPECIAL CARE with MAINS/LINE voltage which can easily KILL YOU. Always be especially careful to leave all electrical circuits in a safe state, so that children, animals or others who are not aware of electrical issues are SAFE from electrocution or any risk consequential on your actions. In some administrations/countries only qualified or certificated electricians are permitted to work with equipment that is permanently connected to the main/line supply. KNOW THE LAW IN YOUR ADMINISTRATION/COUNTRY. NEVER BYPASS SAFETY EQUIPMENT such as fuses or circuit breakers or any safety interlocks. NEVER LEAVE BARE LIVE WIRES ACCESSIBLE. YOU MAY BE LIABLE IN LAW FOR ANY ACTIONS YOU TAKE. Every year some professional electricians are killed as a result of failing to take appropriate precautions - PLEASE BE CAREFUL WITH ELECTRICITY!

Now, I do hope all that got your attention - I don't want any dead or shocked readers. There is absolutely no need to be frightened by electricity - especially here, as we will mainly be dealing with very-low-voltage supplies, which are relatively safe. There is however EVERY reason to be cautious when dealing with electricity - just as you wouldn't put your hand in a pot of boiling water. With boiling water, it's fairly easy to detect that there is a risk, but electricity is invisible, so you must test with something that can detect its presence.

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