Source : Webster's Revised Unabridged Dictionary (1913)

Bumboat \Bum"boat`\, n. [From bum the buttocks, on account of
   its clumsy form; or fr. D. bun a box for holding fish in a
   boat.] (Naut.)
   A clumsy boat, used for conveying provisions, fruit, etc.,
   for sale, to vessels lying in port or off shore.

Source : WordNet®

bumboat
     n : a small boat that ferries supplies and commodities for sale
         to a larger ship at anchor