  Ratchet models are prominent candidates to describe the transport phenomenum
in nature in the absence of external bias. This work analyzes the parameter
space of a discrete ratchet model and gives direct connections between chaotic
domains and a family of isoperiodic stable structures with the ratchet current.
The isoperiodic structures appear along preferred direction in the parameter
space giving a guide to follow the current, which usually increases inside the
structures but is independent of the corresponding period. One of such
structures has the shrimp-shaped form which is known to be an universal
structure in the parameter space of dissipative systems. Currents in parameter
space provide a direct measure of the momentum asymmetry of the multistable and
chaotic attractors times the size of the corresponding basin of attraction.
Transport structures are shown to exist in the parameter space of the Langevin
equation with an external oscillating force.
