The ornamental design for a blowoutpreventer, as shown and described.
FIG. 1 is a perspective view of the blowout preventer showing my design;
FIG. 2 is a right side view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a front view thereof;
FIG. 5 is a rear view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines in the figures are for the purpose of illustrating the environment in which the design is associated and form no part of the claimed design.