  We report results from a high-resolution optical spectroscopic survey aimed
to search for nearby young associations and young stars among optical
counterparts of ROSAT All-Sky Survey X-ray sources in the Southern Hemisphere.
We selected 1953 late-type (B-V >= 0.6), potentially young, optical
counterparts out of a total of 9574 1RXS sources for follow-up observations. At
least one high-resolution spectrum was obtained for each of 1511 targets. This
paper is the first in a series presenting the results of the SACY survey. Here
we describe our sample and our observations. We describe a convergence method
in the (UVW) velocity space to find associations. As an example, we discuss the
validity of this method in the framework of the BetaPic Association.
