The ornamental design for a boattransomplatform, as shown and described.
FIG. 1 is a front, top perspective view of the boat transom platform of the instant invention, showing the new design;
FIG. 2 is a left side perspective view of the boat transom platform of the instant invention of FIG. 1, wherein the right side is a mirror image thereof;
FIG. 3 is a plan view of the boat transom platform of the instant invention of FIG. 1;
FIG. 4 is a bottom plan view of the boat transom platform of the instant invention of FIG. 1;
FIG. 5 is a front elevational view of the boat transom platform of the instant invention of FIG. 1;
FIG. 6 is a rear elevational view of the boat transom platform of the instant invention of FIG. 1;
FIG. 7 is a left side elevational view of the boat transom platform of the instant invention of FIG. 1; and,
FIG. 8 is a right side elevational view of the boat transom platform of the instant invention of FIG. 1.