This is where the magic starts. The alternator is made of three major components and many other minor ones all with important jobs. The housing does just what its name says. It houses all the internal components and provides places to mount the alternator to the engine. The stator is inside of the housing and is comprised of 3 sets of windings. Spinning inside of the stator is the rotor. The rotor is an electromagnet that is spun via a belt and pulley driven by the engines cranks pulley. When the rotor is spun it is also fed an electrical current via the regulator turning it into an electromagnet. The magnetic field acts on the windings creating more electricity. That electricity is passed through a rectifier then to your boats battery.
Here are other important parts of an alternator:
Regulator- This regulates the amount of current going to the rotor. This controls the output of the alternator.
Rectifier- This changes the AC current made in the alternator to DC current for your battery.
Bearings- Support the rotor and allow it to spin freely.
Split Rings and Brushes- Help provide power to rotor.
Fan- Cools the alternator.
Things can get complicated when talking alternators. There are different voltages, amperages, there are internally regulated and externally regulated plus man others. For this blog I will stick to 12 volt. The amperage is up to the boat, its electrical loads, and its use. in most cases the alternator that came on your engine will do the job you need it to. If you find that is not the case or you want to add more loads to your boat an aftermarket alternator with a programable external regulator like what Balmar (https://balmar.net/) offers will fit the bill.
So that is a very basic run down of your alternator. If you want a more in depth description feel free to reach out via email or give me a call.