  An active swimmer can tow a passive cargo by binding it to form a
self-propelling dimer. The orientation of the cargo relative to the axis of the
active dimer's head is determined by the hydrodynamic interactions associated
with the propulsion mechanism of the latter. We show how the tower-cargo
angular configuration greatly influences the dimer's diffusivity and,
therefore, the efficiency of the active swimmer as a micro-towing motor.
