The "good professor" told me
 

Well, he told me -- though it appears he didn't understand he told me -- that
he doesn't know the difference between a rudder and a prop.

My, my, my. but what do you expect from someone trained as an electrical
engineer 34 years ago in a country with more sheep than people who does control
system analysises for MRI equipment who tries to talk boats?

here ya go, professor. rudder, that thingie near the back of a boat; prop,
that thingie that splashes water forward or backward.