The ornamental design for a boatbra, as shown and described.
FIG. 1 is a perspective view of my new design for a boat bra showing the boat bra as it would appear when installed on the bow of a boat mounted on a boat trailer and wherein the boat and trailer form no part of the instant design;
FIG. 2 is a left side elevational view of the design of FIG. 1;
FIG. 3 is a right side elevational view of the design of FIG. 1;
FIG. 4 is a front view of the design of FIG. 1;
FIG. 5 is a top plan view of the design of FIG. 1; and,
FIG. 6 is a bottom plan view of the design of FIG. 1.
The broken lines represent the environment in which the article resides and forms no part of the claim.