[nradov]

Fixed sails won't be viable for container and bulk cargo ships due to the need for unobstructed access. They might be able to make limited use of kite type sails for running downwind.

Sails could be more viable for tankers and car carriers. Those don't rely on cranes for loading and have more free space on deck.

[hinkley]

You could rotate it out of the way in port, assuming you can keep other ships from running into them (I've seen one fixed sale design that collapses like an antenna), but there are wear and tear problems with a mast that is not fixed, aren't there? Especially given the direction and magnitude of the forces we're talking about.