The ornamental design for a yacht, as shown and described.
1.1 is a front, right and top perspective view of a yacht showing my new design;
1.2 is a rear, left and top perspective view thereof;
1.3 is another front, right and top perspective view thereof;
1.4 is a perspective view thereof shown in a first state where a starboard hatchway at a bow port and a beach club at a stern are open;
1.5 is a perspective view thereof shown in a second state where the starboard hatchway at the bow port and the beach club at the stern are closed;
1.6 is a partial enlarged view showing the stern in the first state; and,
1.7 is another partial enlarged view showing the stern portion in a third state where a helicopter landing platform and the beach club at the stern are open.
The broken lines in the drawings illustrate portions of the yacht that form no part of the claimed design.