  The work is a detailed study of rational singularities of multiplicity 3
(RTP-singularities, for short). We give a list of nonisolated hypersurface
singularities of which normalisations are the RTP-singularities, and construct
their minimal resolution graphs by means of a subdivision of Newton polygons of
those -- a method introduced by M. Oka for isolated complete intersection
singularities. We show that nonisolated forms of RTP-singularities and their
normalisations are both Newton non-degenerate.
