  Light curves for more than century optical photometric observations of the
blazar OJ 287 reveals strong flares with a quasi-period of about 12 years. For
a long time, this period has been interpreted by processes in a binary black
hole system. We propose an alternative explanation for this period, which is
based on Doppler factor periodic variations of the emitting region caused by
jet helicity. Using multi-epoch very large baseline interferometry (VLBI)
observations carried out in a framework of the MOJAVE (Monitoring Of Jets in
Active galactic nuclei with VLBA Experiments) program and other VLBA (Very Long
Baseline Array) archival experiments at the observing frequency of 15 GHz, we
derived geometrical parameters of the jet helix. To reach an agreement between
the VLBI and photometric optical observation data, the jet component motion at
a small angle to the radial direction is necessary. Such non-radial motion is
observed and, together with the jet helical shape, can be naturally explained
by the development of the Kelvin-Helmholtz instability in the parsec-scale
outflow. In this case, the true precession of the OJ 287 jet may manifest
itself in differences between the peak flux values of the 12-year optical
flares. A possibility to create this precession due to Lense-Thirring effect of
a single supermassive black hole is also discussed.
