Source : Webster's Revised Unabridged Dictionary (1913)

Mackinaw boat \Mack"i*naw boat\
   A flat-bottomed boat with a pointed prow and square stern,
   using oars or sails or both, used esp. on the upper Great
   Lakes and their tributaries.

Source : WordNet®

Mackinaw boat
     n : a flat-bottomed boat used on upper Great Lakes [syn: {mackinaw}]