The parent hull methodology of hull form design uses an existing ships lines plan, with known performance characteristics, to produce a similar or sister ship. The parent hull can is modified (stretched, scaled, etc.) to suit the requirements of the new design vessel, or to correct undesirable qualities in original. The parent hull approach has the advantages of being relatively quick, with relatively predictable results. Care must be taken, however, not to over-generalize the relationships between similar hulls, particularly in regard to stability (i.e, see Ryan's Commander).