Not quite the same as the two magnets. If you have a big fan and a square sail, you’re moving air, which has mass and is not attached to the boat. That alone will cause a force that moves the boat backwards. The moving air that hits the sail will not fully cancel that force due to frictional losses and air spillage from the edges.

Racing yachts are a different story. They have rigid sails that are shaped like airfoils. Blowing across an airfoil causes lift. So a big fan blowing perpendicular to the axis of the boat across such a sail would move the boat forward. But it’s much more efficient for the fan to blow backwards without the sail, hence airboats and hovercraft.