This invention is directed to a novel amphibious surface vehicle (10) having a hull like chassis (11) with a plurality of rotary engagement devices (14) adapted for travel over various surface terrains and fluidic substances (17). Each engagement device includes rotors (16) having a multi-lobular periphery that provides improved tractive and propulsive attributes. The rotors are coupled through a driven eccentric hub (30) and phased by a non-circular internal gear pair (27, 37) so as to provide synchronized linear motion upon a weight bearing surface (15). The rotors with an overlapping contact ratio which produces increased traction and bearing area translating to improved overall performance upon a planar surfaces (15). This overlapping action becomes more paddle like when surface penetration occurs or by adjusting lever (19) aggressively changing the phasing incidence of the rotors (16), which is conducive to fluidic propulsion on water or other low shear strength substances (17).