Could be faulty grounding at the shore connection that should have dropped out with a direct short on the boat. I think he mentioned that the batteries were off via the Perko switch.

Definitely worth a look.

However...if the switch was left on, it is highly possible that the bilge pump float stuck, overheated the pump and set the boat on fire. That is what happened in 1985 at High Lift Marina at NE 188th Street in North Miami Beach. A boat was brought in and put in one of the lower racks...switch was left on and the bilge pump hung. There were no Fire Sprinklers and the entire dry stack warehouse burned to the ground...first 5 alarm fire in Dade Co. history. I am tuned into this because I installed the Fire Sprinkler System in the Racks and overhead in the new replacement building.

Most Marinas have a strict policy that the battery switches be left in the "All Off" position anytime a vessel is stored or docked on the property. Marine UL listed breakers on docks for shore power have a dead short automatic disconnecting means. If the battery switch was off and there was a short on board between the On Board Panel and the Dockside Breaker...the breaker should have tripped...immediately killing any source of power to create a short from a fire.

Admittedly, all this is speculative but entirely possible.