Homemade hovercraft used to be a big thing since at least the '50s or '60s (and for all I know still are). Typically made by putting a prop on a vertical-axle lawnmower engine and building a simple vehicle body with a fan shroud in the middle.
There was a classic disaster that happened to a LOT of people who did this:
After they'd played around on land with it for a while they'd decide to test how it would perform on water. So they'd take it down to the local park-on-a-lake, fire it up, and drive out onto the lake.
It would work fine
Then the spray it was kicking up and sucking back around the motor on its way to the fan would finally short out the spark wiring. Oops!
Of course they usually hadn't included any floats...