A motorboat of some kind, but it didn't sound like a very powerful one.
"The Wailing Octopus"
Harold Leland Goodwin
One thing leads to another, and suddenly a stranger is trying to run you down with a motorboat."
"The Wailing Octopus"
Harold Leland Goodwin
He was living at home now, nominally secretary of a strong corporation-practically eating, smoking, drinking, theater-going, lounging at the Varsity Club, and playing with his speedy motorboat.
"Our Nervous Friends Illustrating the Mastery of Nervousness"
Robert S. Carroll