As typically embodied, the present invention's add-on device includes two wedge-shaped structural components that are oppositely congruent and symmetrically connected. In profile, the device describes a pair of nearly triangular quadrilateral figures that are enantiomorphs (mirror images) with respect to the linear bisector (mirror line) at which they join. The device's V-angular upper surface defines the same V-angularity (“deadrise”) as does a V-angular hull bottom, the device thus fitting beneath the hull bottom. The device's V-angular lower surface defines a different angularity, which is imparted to the hull bottom when the device is attached thereto. According to typical inventive practice, the device alters the hull bottom's V-angularity by at least 1° and, at least, covers approximately 100% of the hull bottom's widthwise expanse along approximately 50% or more of the hull bottom's lengthwise expanse. The device modifies a marine vessel's hydrodynamics and/or hydrostatics, and may provide armor and/or wear benefits.