Step 1: How to Sink and Burn Your Boat Without Doing Anything

Captain Victor and Captain Kenny were already at the boat.
We got out the pumps and started working.
Here's the boat with most of the water pumped out. The water was shin deep above the floorboards when we got there. It took us about half an hour to pump it out with the two hand pumps. The "gusher" lever/diaphragm pump was a lot faster than the pvc piston pump.

How did it happen? The boat has a slow leak through the rusted stern tube. When the water gets high enough to lift the flap on a float switch it turns on an electric bilge pump which runs for about ten seconds and pumps out the water. Those little pumps are the size of half a beer can and work really well. Until they stop working. One of them died and we didn't notice, because the other pump kept working and the boat stayed dry. Each pump is wired to a separate battery. Eventually the other battery died a natural death.

We went sailing on a sunday. Everything was fine. Some time after that the remaining pump quit doing its thing. The boat slowly sank at the dock. When the water got high enough it reached the end of an extension cord that was hanging off the side of the counter.
The 120volt AC started arcing and fizzing, making clouds of steam and smoke. The neighbors noticed the burning smell and came to investigate. It's actually a really lucky thing, because without the fire, no one would have noticed the boat sinking until much later. We don't know how low the boat could have gotten, would it have sunk to the bottom and flipped sideways hanging from the dock lines? Fortunately we didn't have to find out.

Step 2: The Burned Out Extension Cord That Saved Us

Here's what the end of the extension cord looked like after it saved our boat.
The two prongs in the connector dipped into the bilge water and shorted out, boiling the water making lots of smoke, fog, and stink.
This alerted our neighbors that our boat was malfunctioning.
Fortunately the seawater resistance over this gap was high enough that it didn't just blow the circuit breaker.