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Essential boat electrics

Small yachts and power boats have 12-volt DC (direct current) systems, although larger vessels will have 24-volt electrics. In most cases the system is split into two parts, one for starting the engine, the other for running all the other electrical equipment on board. There are usually two batteries (or banks of batteries) to ensure there’s always a well-charged battery for starting the engine that’s never used for anything else. In some cases there will also be a third system, with another dedicated battery (or bank of batteries) for powering high current equipment such as electric windlasses, bow thrusters and electric winches.

AC systems

Larger boats often have an alternating current (AC) generator to power domestic electrics. The generator can also charge the DC batteries instead of  using the main engine.

The more common type of AC system relies on connecting to shore power when the boat is docked. This can be used to run domestic appliances and also to charge the batteries. Note that AC and DC systems must be kept separate.

Electrics inspection checklist

With the boat ashore, here are some recommendations for carrying out a boat owner electrics inspection. Safety is always paramount so remember to do the checks with the batteries off. Wearing a head torch helps, make notes as you go and only tackle a repair if you are 100% sure you know what you are doing:

Wiring checks

  • Labelling – the idea of labelling where each wire connects to and from may sound time consuming but will pay dividends when you or your electrician need to source a component’s wiring in a hurry. Being organised here will really be of help and save you money in the long run.
  • Wiring diagram – refer to your boat’s wiring diagram as you carry out the inspection. If you don’t have a schematic of all the boat’s equipment and wiring plan, then it would be a good idea to sketch one out. This will also be invaluable when troubleshooting faults.
  • Chafing – check the condition of the wiring for any signs of chafing, or exposed wires. This can be caused by vibration of wires that are not properly secured rubbing against things or where wires pass through bulkheads. This happens when wire are not properly protected by conduit and suitable grommets or have come into contact with sharp objects. At very worst protect with electrical tape, but exposed wiring should be replaced with new marine grade wire as soon as possible. Also at the same time you will need to fit suitable conduit, grommets or padding.
  • Melted wires – wires that overheat are a serious fire risk and need to be sorted out as a priority. Look for signs of melted wiring insulation, caused either by overloaded wires becoming very hot or from being in contact with a hot engine. Ensuring wires don’t come into contact with hot engines is easy enough to fix. However, wires that overheat need some troubleshooting to determine the cause. This might entail replacing with thicker wire to suit the power draw of the components they connect to and/or protecting with more appropriate fuses (see below). If in any doubt this is time to call in professional help.
  • Fuses and circuit breakers – fuses need to be rated lower than the wires they are protecting and lower than the components they connect to. Check all wires are protected by a fuse or circuit breaker.
  • Connections – check the wiring for weak connections, tighten or replace any that are loose and check for corrosion. Poor connections that are not properly installed or corroded are also fire hazards. Note: do not use electrical tape to repair a connection.

Battery checks

  • Battery connections – check the condition of the battery connections. Check for tightness. Clean and coat with petroleum jelly.
  • Battery straps – check the batteries have remained secure and the retaining straps are in good condition and have not become weakened.
  • Battery top up – unless they are maintenance-free type, check battery levels and top up with distilled water if necessary.
  • Battery condition – test batteries to confirm capacity. Check batteries are kept clean and dry. If the boat is ashore over the winter, consider taking the batteries home for storage as they will last longer. Note – I have done this for the past 7 years with my current batteries and they are still in good condition.

Alternator checks

  • Belt tension – check the belt tension. This should be enough to allow the belt to be depressed by 12mm or so when pushed down by the thumb.

Equipment checks

  • Navigation lights – check all navigation lights are working correctly. Make a note of any bulbs that need replacing and add to the to do list. The most likely causes of a bulb failure are either that it is blown or the contacts have become corroded. Masthead lights can suffer from voltage drop as there is a long cable run from the battery to the top of a mast and resistance in the wire can become excessive. Consider replacing with thicker wire if this is the case. Corrosion of the bulb contacts and connections need to be checked and cleaned up first, using fine emery paper. Also check deck connectors are in good condition. Also check lens seals are in good condition and are not allowing ingress of water into the light.
  • Exterior bulbs – clean exterior bulb contact points, including deck lights. Spray with anti-corrosion spray.
  • Interior lights – check all interior lights are working. Make a note of any bulbs that need replacing and add to do list.
  • Bilge pumps – check the float switch and manual override switch of the bilge pumps are working correctly. If not, check the connections and fuse leading from the battery to the pump. Note a bilge pump is one of the only pieces of equipment that should be wired directly to a battery via its own fuse to ensure it will work if the batteries are turned off.
  • Instruments – test all the instruments are working satisfactorily and carry out any annual maintenance recommended by the manufacturer’s operator manual. Clean instrument screens with plasma screen cleaner.
  • Solar panels – check electrical connections are in good order and secure.

 

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