  We present a simple model for the apparent superluminal motion along curved
trajectories of features observed in the compact radio jet of the quasar 3C345.
The model is inspired by the magneto-hydrodynamic approach of Camenzind (1986),
and assumes a conical geometry of the jet within about three milliarcseconds of
the radio core. Simultaneous conservation of three out of four physical
parameters is used to derive analytic solutions for the equation of motion of
the idealized jet features. These are the jet's kinetic energy, angular
momentum, and momentum along the jet axis. Conservation of angular momentum is
required to fit the observed trajectories at distances larger than 3
milliarcsec, in agreement with the kinematic predictions of Camenzind's model.
The best-fit model variant preserves angular momentum, kinetic energy, and
opening angle, with an inclination of the jet axis to the line of sight 6.8
degrees, an opening angle 0.95 degrees, and Lorentz factors 5.8 and 4.6 for
components C4 and C5, respectively (H_o=100 km/(s Mpc)). The model ignores
turbulent small-scale motion of the jet components, and it does not take into
account the overall bending of the jet beyond about 4 milliarcseconds,
restricting it's applicability to the inner few milliarcseconds from the core.
