Propulsion

You start with an engine, a dive shaft, and a propeller.  Simple and beautiful.  ...and then it starts to get complicated.

You want to be able to go fast when you need to out run a storm or meet a deadline. You want to be powerful when loaded down in heavy seas off a lee shore. You don't want to waste fuel. You want to optimize free wind and solar power.  You want to be able to fix it yourself. You want a backup plan if fixing is not going to happen quickly.

See where these criteria took us.  Junk Sails, Background Info, Propeller, Controllable Pitch, Diesel/Hybrid/Electric