Abstract
We examine spherically symmetric self-similar spacetimes in comoving coordinates, subject to a monotonically increasing comoving time to the future, and find the necessary conditions for the formation of naked strong curvature shell-focusing singularities. The strength is shown to be persistent (not instantaneous). On the basis of eikonal perturbations along the associated Cauchy horizons we find no reason to suspect that the singularities are unstable.