Nasty story time. After Hurricane Luis I was asked to go down to a 38 footer to just run-up the Yanmar to check it worked. After checking for a clear flow of water to the strainer I cranked her over.
So as she started the starter motor stuck, the throttle stuck wide open and the engine was just screaming at full revs. The shut-off solenoid did not work and no manual over-ride.
Then I noticed the 4D engine start battery started to spout 4inch blue flames from the breather holes on top of the top-up caps.I had to grab a big kitchen knife and a washing-up rubberglove and chop the fuel line and the positive cable quickly.
Very frightening, very quickly. All this inside the saloon.
Good battery switches and even a VSR (voltage sensetive relay) an ARS or BRS is a must, this will stop any voltage returns when ......er not required.
Not nice.
Fish