Marine Electrics Made Simple or How to Keep the Batteries Charged

By John Champion

Marine electrics are mostly misunderstood by cruising sailors, the people who need the most understanding. This small book describes in simple detail, in plain language how to keep the batteries charged and the options available to do this. It does not attempt to get technical but instead concentrates on the practical understanding of the issues so you can make informed decisions and understand the benefits. Not a serious book the 11 chapters contain a lot of fun in addition to good information.

• Language: English
• Publisher: John Champion
• Release date: Sep 16, 2012
• ISBN: 9781301413539

John Champion

The author, John Champion is currently living aboard in Malaysia after a three year stint working in the marine electrics industry in Thailand. A regular writer for sailing magazines he has lived aboard since 1999 and sailed perhaps 22 000 sea miles. Much work in sail training and the charter industry has allowed him to test many dozens of different yachts and catamarans. He now needs a bigger boat so please buy a copy for a friend!

Book preview

Marine Electrics Made Simple

Or How to Keep the Batteries Charged.

John Champion

Smashwords Edition

Copyright 2012 John Champion

Chapter 1. How much energy do you need?

The wind is free and yachts use this energy to get around. A good deal when you consider the amount of fuel necessary to get up the coast or make a passage, never mind a circumnavigation. Additional energy however is still required to make a yacht comfortable and convenient. Electricity is the ideal stuff for this and we rely on it to run fridges, autopilots, lights, navigation equipment and plenty more.

Generating, storing and distributing electricity on a yacht is no easy feat and the more gear we add the more complex and critical it becomes. If we are tying up in the marina most of the time the task is easier, shore power will supply the solution but a cruising boat needs to be largely self sufficient in this area. Easier said than done and a properly balanced DC electrical system will set you back a good many bucks. Initially costly yes, but cheaper in the long term and far better for your sanity. I wonder how many cruising dreams and relationships have soured because of power related boat problems? No lights, a fridge full of spoiled food, no music, no showers and maybe no engine when it was really needed.

There is considerable science involved in obtaining an efficient and reliable DC (direct current, usually 12 or 24 volts in most yachts) system. In many cases professional advice and installation are required but understanding some of the basics will at least help in selecting equipment and comprehending a little of what the sparky or brochure is saying.

Calculating electrical requirements

This is perhaps the starting point for a reliable DC system, get this right and all should work, get it wrong and go through the expensive process twice. Estimate, (calculate through experience is better) the electricity your vessel will require for an average day and add 20% for fun. Check the current draw of items and calculate the consumption over a 24 hour period.

Item Time run Consumption

Fridge 4 amps for 12 hours = 48 amps

Lights 2 amps for 4 = 8 amps

Pilot 4 amps 12 hours =48 amps

Instruments 2 amps for 12 hours =24

Pumps 3 amps for 0.1 hour = 0.3 amps

Stereo 2 amps for 12 hours = 24 amps

Total for the day a whopping 152.3 amps!

So on a day sail of twelve hours our consumption will be around 150 amp hours for the 24 hour period, more for a passage when nav lights are used, less when at anchor and the autopilot is off. Add 20% and the figure becomes 180 amp hours. If we wish to discharge the batteries to no less than 50% we need a minimum 360 amp hour bank. So generating at least 180 amp hours each day is the target and the methods of achieving this