Many moons ago, when I was a teen, my friend borrowed his dad's boat. He hitched the trailer up to his truck and picked me up at home. Right before the boat launch ramp the road had a couple of large dips, a right sweeping turn, and a stop sign. He negotiated the turn and came to a stop. As he slowed down we noticed the boat/trailer passing us on the left. The front was riding on the retracted tongue jack wheel. It continued past us, missed all the trailers parked at the launch area, and went down the ramp, all on it's own.
The boat ended up floating with the trailer attached to it. With some help we managed to recover the boat and turn it around. We tied a rope to the trailer, launched the boat off it, and pulled the trailer to shore.
It turns out that he had not lowered the hitch ball latch or attached the safety chains.