Hmm.. don't know the name.. but those things are the "sails"
Airfoils, or whatever they are called.. kind of like vertical aircraft wings.
The airfoil shape means that air has to travel further over one edge than over the other. This creates a pressure difference and with aircraft, this creates lift, and here on the ship, that "lift" is directed forward so it creates forward movement.
Now to look for the name.. hmm.. heheh..
Fred