Electrics are the hidden but essential part of any cruising boat. Nothing will work without a good electric system. So many problems occur during an extended cruise because of breakdowns in electrics. If you cannot start the motor, it is usually an electrical problem. The navigation instruments go on the blink and it will be found to be a power problem. Other items, such as refrigeration, lighting and communications, will not operate without a steady supply of sufficient power. The quality of the original build, including wiring looms, determines how well everything works of course. Often one of the problems is that the original power designer never dreamt of the size and number of extra electrical units that will be put into the boat. These “add ons” can often be the cause of flat batteries as time goes on. If you take up the cruising life and do not know much about 12v electrical systems then it will become a steep learning curve. To keep a cruising boat operating requires constant attention to the power supply. I well remember my first cruising boat which appeared to have been fitted out by a spider, with wires running everywhere. So when purchasing a secondhand yacht you need to make a careful study of wiring system throughout the yacht.
Like the human body, where the heart is the power supply, the boat's heart is its battery bank. Think of the batteries as a water reservoir where to keep it full you need to replace what you use. Boats that are not used full-time will nearly always have insufficient battery power. Having sufficient storage is the first requirement. Following on from there is the strength of the wiring. This is not a physical strength but a power strength. You cannot push high amps through thin wires. Heavy wiring is a must and too heavy is much better than too light. So, the higher the amps the greater the diameter of cable required. Next, is having sufficient reservoir and big enough channels to transport it is useless if you do not have the ability to keep topping up the supply. This is done by the alternator on the main engine, or by a generator set, solar panels or wind generators. It is up to the owner to decide how many of these systems are installed. Most regular cruisers will install all of them. You can never have too much power; it is the installation that creates the problems. On top of all this is the constant maintenance of the whole system. There is not much point in regularly checking oil levels in the generator set if you have bad wiring connections. But beware, it is often the wiring you cannot see that will cause you the trouble.
Let us start with the batteries. You need to look at all the electrical items on board and sit down with a notepad to work out the average daily consumption. Add about one-third to that figure and you will be close to the mark. Then compare that with the amount of amps the batteries hold and the figure you come out with should be well over half of your reservoir. Batteries do not like being drawn down to less than 50 per cent. You will need a dedicated battery just for starting your engine and this should be full of power at all times. You should have two or three house batteries that will be deep cycle type batteries to run all the rest of the electrics. A heavy-duty battery switching system is usually required, to feed power into each battery individually or join them all up together. Absorbing all this information is part of the steep learning curve I mentioned earlier. To help you understand all this, the wiring on the boat should be neat and easily traceable. Another tip: the further you push power it breaks down. For instance, you may have 12v from the battery but by the time it reaches the bow of the boat to operate the anchor winch you may only be delivering 11v. The size of the wire is so important. Due to the seawater environment, it is best to used tinned wire as it has more resistance to corrosion than copper wire.
Another tip: try not to add on to an already busy circuit. If you fit a new item then run the wires right back to the switchboard (and fuse) rather than link the wires in with a nearby unit. This puts added load on both units. So when adding new units consider carefully the route of the wire and the quality and strength of the crimps and joiners. These are the sort of places that give the most trouble.
Replacing the power in the reservoir is the hardest and most expensive system. Usually the alternator on the main engine is too small. Nothing smaller than 80amps will do and a standard frame 120amp might be a good investment. To complement this unit you also need a smart regulator. A standard regulator will not produce enough power to charge the batteries quickly enough. Proper amp meters will be required to monitor the power being supplied to the batteries from all sources. So if you have solar and wind generator then you will need three separate amp meters. You need to know at any given time how much power is being replaced by each item. It is a good idea to know how much power you are using at anytime as well.
The key to all this power supply is maintenance. While you are busily fitting new items, the saltwater environment is doing its best to destroy them and the wiring. Especially in wet areas where bilge pumps and float switches operate. So these should be tested frequently. Every so often you should open up the switch board and check all the joiners and give it a spray with WD or INOX. Battery terminals should be removed and cleaned every couple of months to ensure a clean flow of power. Also, when was the last time you checked the wiring at the anchor winch and switch? To keep that power flowing the connections must be clean and tight.