Here's a real nutshell explaination.

Well, on an outboard, the Stator (winding) is made under the flywheel
instead of being configured into abelt driven package. Instead of a
field rotor, (automotive) the Yamaha has magnets mounted inside the
flywheel to draw a field. the automotive alternator, is actually a
3-phase DC generator (for lack of better terms) while the outboard is 2
phase.

they both do the same thing, jsut way different ways of doing it.

Tim