Prop torque...a prop turning clockwise would cause the starboard side to lift somewhat. On the right side to balance this effect.
Happy Thanksgiving!
I don't think that's quite correct. It goes back much, much further than the propeller does. I believe it dates back to the days when boats were controlled by the "steering board". Basically, the steering board was a rudder most commonly attached on the right side of the boat (since most people are right handed). This is also where the term starboard came from. Now when a boat was brought in to port, it was tied up on the opposite side of the steering board (or the left side). This is where the term "port side" came from.
Ye, the Brittish way, and you are correct. Red right return and docking to port played a part in this.
I do think manufactures these days take in to consideration prop torque. Least they tell me so.
Interesting question, maybe an engineer will clarify this more.