  We developed an algorithm to use Galaxy Zoo 3D spiral arm masks produced by
citizen scientist volunteers to semi-automatically classify spiral galaxies as
either multi-armed or grand design spirals. Our final sample consists of 299
multi-armed and 245 grand design galaxies. On average, the grand design
galaxies have smaller stellar masses than the multi-armed galaxies. For a given
stellar mass, the grand design galaxies have larger concentrations, earlier
Hubble types, smaller half-light radii, and larger central surface mass
densities than the multi-armed galaxies. Lower mass galaxies of both arm
classes have later Hubble types and lower concentrations than higher mass
galaxies. In our sample, a higher fraction of grand design galaxies have
classical bulges rather than pseudo-bulges, compared to multi-armed galaxies.
These results are consistent with theoretical models and simulations which
suggest that dense classical bulges support the development and/or longevity of
2-armed spiral patterns. Similar specific star formation rates are found in
multi-armed and grand design galaxies with similar stellar masses and
concentrations. This implies that the specific star formation rates in spiral
galaxies is a function of concentration and stellar mass, but independent of
the number of spiral arms. Our classifications are consistent with arm counts
from the Galaxy Zoo 2 project and published m=3 Fourier amplitudes.
