What are these?

[steveeasy]

I’m sat waiting for a trailor to come off a ship. Yep I have to work. Just noticed these things on the tub. The rotate. What could the be

 

[andsarkit]

Rotor ship. I wonder how well they work. Any chance you could get up to the bridge and ask them?

 

[VicS]

Rotorsail wind propulsion

https://sea-cargo.no/wp-content/uploads/2022/10/SC-Connector-produktark-2022-1.pdf