It sounds like you're describing a DeHaviland Canada Twin Otter.

Check out the link for a picture..is that it?

http://www.etl.noaa.gov/technology/i..._otter_cropped.
jpg





It did look a lot like a Caravan, but it was a twin. It
had same look as a Caravan like it is carrying a boat
under the fuselage.

-john-