During Season 1- Season 3 there were several faceless boats, one was green, black, white, and red, one was light yellow, with a red hull with a white stripe in the middle, one was an old steamship who was white, light yellow, and light blue. Another one, based on the RV Calypso, had a white hull, and its model was later used for Rebecca.
These boats do not have any speaking roles.
The little red boat appears in Season 1 - Season 2 , The a blue vessel appeared in Different Strokes - Different Boats. The green one appeared in Seasons 1-3, the steamship in Season 1 only, and the research vessel, later reused for Rebecca in Theodore's Bad Dreams, only appeared in Season 1.