It's not at the equator that the problems occur; it's a few degrees north and south of the equator. Coriolis force from the earth's rotation causes the same airflow patterns that make the trade winds...
Sailing is a sport that requires the changing of the rigging and rudder on a boat to change the direction and speed of the boat. The boat is moved by wind against the sails.
It's what you hammer into the planks to build a boat. ;) Tack: v. To purposely change the direction of the boat by moving the sails to the opposite side, in order to avoid shallows, rocks or other...