The ornamental design for an element of a floatingplatform, as shown and described.
FIG. 1 is a top and front perspective view of an element of a floating
platform showing my design, the bottom view thereof being plain and not
forming part of my design; and,
FIG. 2 is a rear perspective view of the element of a floating platform
shown in FIG. 1 nested with three other elements of a similar
configuration.