The very thing happened to a cousin of mine. Luckily he didn't get out of the harbor before it blew up, so there were a few people nearby to pull him out of the water.
As a kid I was always scared to death of blowing up the boat and always ran the blowers plenty and/or lifted the cowling.
My older sister has a boat and doesn’t seem too worried about it. “Oh - there’s a breeze today, that is good enough.” So far so good, but I hate being on her boat!