  This series of papers explores the evolution of late-type galaxies in the
rich cluster Abell 85. Here, we revisit the complex dynamical state of A 85 by
using independent methods. We analyze the redshift distribution towards the
cluster out to 40,000 km/s, and determine the mean redshifts of the background
clusters A 87 and A 89. We then search for substructures in A 85 by considering
the 2-D galaxy distribution for its members and by applying the kinematical 3-D
Delta-test to both projected positions and radial velocities. This clearly
reveals several substructures that we describe. We also analyse the
distribution of the brightest blue galaxies across a major fraction of the
cluster volume, considering if they are gas-rich or poor. We report a very
asymmetric distribution of the blue member galaxies, and connect it with
substructures revealed in the optical and X-rays. By matching our sample of
bright blue member galaxies with HI detections reported in the literature, we
identify gas-rich and gas-poor ones. HI-rich blue galaxies also turn out to be
asymmetrically distributed, with most of them projected on the eastern side of
the cluster. No blue objects have been detected in HI up to a projected radius
of 2 Mpc in this zone. We estimate the ram pressure stripping exerted by the
intra-cluster medium as a function of the projected distance from A 85, and
quantify how important this mechanism may be in sweeping the gas out of the
infalling spirals.
