Yep, in the last few years, there's been quite a lot of movement in the shipping industry to add wind-assist devices to existing/new ships. Michelin [1] is basically doing what you suggest. Maersk and Cargill [2] are also working on technologies that harness wind to decrease fossil fuel use. Oceanbird [3] is working on wing-style sails that they claim can basically move a cargo ship along at ~10kts.
How does one even attach a sail to a cargo ship that would move it at 10 knots? I'm not an engineer so it might even be obvious, but it seems like the mast would have to exert an incredible amount of force on the ship.
Then again, I guess the same applies to old sailing ship and they figured it out. It just boggles my mind.
Traditionally I believe the masts were held vertical by ropes, I imagine the force transferred through them (by tension) not the stiffness of the mast. But I'm far from an expert.
Then again, I guess the same applies to old sailing ship and they figured it out. It just boggles my mind.