We don't have synonyms for mackinaw boat yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are mackinaw coat.
(n) :
(historical) A flat-bottomed cargo boat, resembling a canoe, often schooner-rigged, formerly used on the Great Lakes and the Missouri River (to a lesser extent, elsewhere).
(n) :
(historical) A flat-bottomed cargo boat, resembling a canoe, often schooner-rigged, formerly used on the Great Lakes and the Missouri River (to a lesser extent, elsewhere).