  Most ULXs are believed to be powered by super-Eddington accreting neutron
stars and, perhaps, black holes. Above the Eddington rate the disc is expected
to thicken and to launch powerful winds through radiation pressure. Winds have
been recently discovered in several ULXs. However, it is yet unclear whether
the thickening of the disc or the wind variability causes the switch between
the classical soft and supersoft states observed in some ULXs. In order to
understand such phenomenology and the overall super-Eddington mechanism, we
undertook a large (800 ks) observing campaign with XMM-Newton to study NGC 247
ULX-1, which shifts between a supersoft and classical soft ULX state. The new
observations show unambiguous evidence of a wind in the form of emission and
absorption lines from highly-ionised ionic species, with the latter indicating
a mildly-relativistic outflow (-0.17c) in line with the detections in other
ULXs. Strong dipping activity is observed in the lightcurve and primarily
during the brightest observations, which is typical among soft ULXs, and
indicates a close relationship between the accretion rate and the appearance of
the dips. The latter is likely due to a thickening of the disc scale-height and
the wind as shown by a progressively increasing blueshift in the spectral
lines.
