  Spiral structure can contribute significantly to a galaxy's luminosity.
However, only rarely are proper photometric models of spiral arms used in
decompositions. As we show in the previous work, including the spirals as a
separate component in a photometric model of a galaxy would both allow to
obtain their structural parameters, and reduce the systematic errors in
estimating the parameters of other components. Doing so in different wavebands,
one can explore how their properties vary with the wavelength. In this paper,
second in this series, we perform decomposition of M 51 in 17 bands, from the
far UV to far IR, using imaging from the DustPedia project. We use the same 2D
photometric model of spiral structure where each arm is modelled independently.
The complex and asymmetric spiral structure in M 51 is reproduced relatively
well with our model. We analyze the differences between models with and without
spiral arms, and investigate how the fit parameters change with wavelength. In
particular, we find that the spiral arms demonstrate the largest width in the
optical, whereas their contribution to the galaxy luminosity is most
significant in the UV. The disk central intensity drops by a factor of 1.25--3
and its exponential scale changes by 5--10\% when spiral arms are included,
depending on wavelength. Taking into account the full light distribution across
the arms, we do not observe the signs of a long-lived density wave in the
spiral pattern of M 51 as a whole.
