Rotor Sails in action

Have you seen the two 30-metre tall rotor sails onboard Maersk Pelican in action?

[thefinestsake]

If we've been putting rotors on ships since the 20s, with them even proving themselves more efficient . . . why are they so uncommon?

[jyk]

the tubes look symmetrical. How is the thrust directed?

Can the direction of the propulsion be changed or is it always in a certain direction - if the wind direction changes, the thrust is no longer straight ahead?

[HonsHons]

Does the rotor sail need an engine to spin too or does it solely rely on the wind?

[mojojojo_BB]

What is the purpose of the disk/flat top? Why is it so large? Thank you.