Electrical Systems & Power Possibilities

Andrew read in a book I bought him that we needed to work out a ‘power budget’ to figure out how much power we were going to need to run the various things on board. You can then work out what the best way is of producing that power

Here are the things that will be run on the electrical system:

  • Starting the motor
  • Interior Cabin lighting
  • Navigation lights
  • GPS and other instruments
  • Autohelm
  • Compass light
  • VHF Radio
  • Stereo
  • Fridge/Freezer
  • 12v Charger for phones etc
  • Inverter for charging cameras, laptops etc

Nice to have:

  • Printer
  • Coffee Machine

Things to look for when purchasing a yacht

  • Location of lighting in all areas
  • Does it have the option for red lighting at night
  • Is there an inverter
  • Where are the batteries and battery switch located?
  • Does it have an inverter?
  • Does it have solar panels or is there a convenient place to position them?
  • Location of navigation lights
  • Are there spreader lights?
  • Location of VHF aerial
  • Location of GPS aerial (it should be low and not blocked)
  • Is the fridge/freezer run on electrical power? (Wildwood’s is run off the motor and it is a pain not having a consistent temperature in the fridge when you are on board for a week – but it is fine when you are just sailing for the day!)

Also it would be great to get a copy of the electrical layout of the yacht so if anything does go wrong it will be useful to refer to that.

Here are some things that I have learnt about electrical systems on board:

  • A battery is a storage facility containing units called ‘amp hours’
  • Every electrical thing on board uses current which is measured in amps. (If it draws 5 amps it means it uses 5 units in the battery in an hour)
  • Its demand is expressed in ‘watts’
  • The power to push the amps down the wires is called ‘volts’
  • Watts = Volts x Amps or Amps = Watts/Volts
  • So a 25 Watt lightbulb in a 12 volt system draws 25/12 = 2 amps (so it uses 2 amps per hour)
  • No battery can really deliver as much as manufacturers claim so a 110 amp battery may be limited to say 65 amps.
  • Yacht batteries are topped up by an alternator driven by a belt from the main engine and the alternator is measured in amps – so a 50 amp alternator can effectively put 50 am hours in to a battery. (However as a battery ages, it becomes harder to charge and takes longer to charge)

So my next job will be finding out how many amp hours all those things use, and then working out how we are going to produce the power! I think solar will be good, but if you are days at a time in cloudy and rainy storm conditions it wouldn’t be much fun if you ran out of power to use the auto helm. I will research the options and note them in this post later.

Update May 2014

I have just read a fantastic article by Ellen Leonard regarding wind vs solar panels. There are some great suggestions in here in regards to the various options for power production. Ellen makes some good points in here, one being that if you are sailing downwind, the wind generator doesn’t create enough apparent wind to generate any kind of power. The other option is towed generators, they are deployed from the stern and as they are towed through the water they spin and produce electricity. Sounds like a great system, but they don’t sound overly popular from what I have read so far. If you are in a marina or at an anchorage for a while then this isn’t going to help much, and there are potential issues with a fish eating it or getting it tangled in the propeller if you forgot to bring it in?! I would like to avoid having a generator. They are noisy and require fuel, but by utilising the power of the wind or sun, or even sea I think we can be more self sufficient and environmentally friendly!

So it looks like it might be solar panels for us. Ellen recommends some different types in her article. I will check them out.


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