We don't have synonyms for slipways yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are slipway, shipway and shipways.
(n) :
(nautical) A sloping surface, leading down to the shore or to a river, on which ships are built, repaired or stored and from which they are launched.
(n) :
(nautical) A sloping surface, leading down to the shore or to a river, on which ships are built, repaired or stored and from which they are launched.