The ornamental design for a boat, as shown and described.
FIG. 1 is a left side elevation view of a boat showing the new design;
FIG. 2 is a rear elevation view thereof;
FIG. 3 is a front elevation view thereof;
FIG. 4 is a top plan view of the upper deck thereof; and,
FIG. 5 is a cutaway top plan view of the lower deck thereof, taken in the direction of line 5-5 in FIG. 3.
The broken lines and unshaded surfaces bounded by broken lines are for the purpose of illustrating portions of the article that form no part of the claimed design.