[cjlars]

Why is a retracting mast preferable to a freestanding rig with, e.g. a roller furling main or a nonsuch style wishbone boom? Is there a physics reason or is this a pragmatic trade-off to fit under bridges and stay out of the way during loading?

[wongarsu]

Typically attempts to fit sails on moderns ships (like the rotor sails that have been installed on some ships in recent years) are targeted at ferries or tankers, exactly because of the loading/unloading topic. Putting large structures on a container ship will interfere with the cranes. And the SC Connector launched in 2021 can tilt the rotor to fit under bridges, with sails half as high as what OutSail tries to do [1]

1: https://www.rivieramm.com/news-content-hub/sea-cargo-ro-ro-w...

[ArpanRau]

Retraction is pragmatic: Air draft and loading/unloading concerns. Wings because they perform much better than traditional sails when installed on ships that are already powering forward at speed.