I believe you need to distinguish between skills in navigation, skills in using sails for catching the wind as power for moving the ship from A to B and skills in keeping the ship afloat and and the maintainance of the different parts of the ship.
Considering using sails as means for moving, it is fairly easy to learn how to sail and quite difficult to learn how to sail well.
If you plan to sail in coastal waters you need skills in reading charts and tidal water tables.
If you plan to sail the ocean you will also need to know quite a lot about how things work in your ship, because something is bound to happen sooner or later and you will have to repair it yourself (electricity, motor maintenance, the plumbing system of the toilet (particularly if you appreciate the companionship of ladies) etc.
Use your head, ram the wall till it falls.