  From a recent study of a stationary cylindrical solution for a relativistic
two-constituent superfluid at low temperature limit, we propose to specify this
solution under the form of a relativistic generalisation of a Rankine vortex
(Potential vortex whose the core has a solid body rotation).Then we establish
the dynamics of the central line of this vortex by supposing that the deviation
from the cylindrical configuration is weak in the neighbourhood of the core of
the vortex. In "stiff" material the Nambu-Goto equations are obtained.
