It's very simple. Break it down to it's core component. "How do you stop a run away boat". Not "How do you PREVENT a run away boat." You're just an asshole, it's not my fault.
Example : Guy sitting in boat driver seat. Has heart attack. Slumps in seat, but still there. Killswitch still in. How ya gonna stop it. If you can't answer just say so.
lol I'm just an asshole? You apparently can't come up with a reasonable debate so you start name calling? Well if you wanna asshole I guess I'll be one.
Since you can't grasp this concept let's spell it out for you. Let's look at youre example; guy has a heart attack in a boat.
Any halfway smart person that has been around boats for longer than ten seconds knows that on any single engine boat design, standard rotation of the propeller is right hand rotation. So anyone knows that when you take your hand off the wheel, and given enough time, that rotation of the propeller will overcome the steering wheel and will make the boat steer a hard right. And even in a jonboat, when the boat takes a hard right and you're unconscious, you WILL NOT stay in the seat. And if the kill switch is hooked to your body as the law requires, it will kill the engine.
Now there again, if you didn't hook it up, or you didn't verify that it works, that's your problem. The only ways to stop a runaway boat at that point would be a remote kill switch (yes they make them) a remote fuel cut off (yes they make them), a dukes of hazard side by side switcharoo, or a damn good shot with a rifle.
Now then you got what you wanted, so shut up and troll somewhere else.