The guess was a short on a bilge pump in the aft end of the vessel. The short being prior to the fuse. That then had the insulation on the curcuit go POOF! After that insulation went poof the other electrical items in the "bundle" had the same event and well all bets off as to what gets hot , shorted, etc etc.
It then becomes driven by a large 12 V house bank and well 50 amps of shore power. Disconecting the actual shore power cord really makes a difference
. Cause the power turns the inside of the boat into one really big stove.
I always find the life of electrical items interesting to watch through a fire. Lights come on and off, even the horn started with a wierd note or two , the windlass makes noise etc etc. The sound of a boat in real pain.
I was on a 34' express cruiser way back when. Cruisin along with the owner up on the Fly Bridge ( aka dodger ). When all of a sudden a log jumped out in front of us.
The boat jumps over the log , both gas power plants go into high RPM till she gets shut down. Then there be steam coming from the cabin cause the power is located under the cabin sole. Off the bridge I go to check out how much water we be pulling. Get into the cabin pull the floor hatch and F&( that smell. Poof thats not steam its oil smoke and thats not water that's FLAME! I drop the floor , grab a dry chem as the cabin fills with toxic smoke. Open the floor hatch , dump the contents of the dry chem. Flames go away for a second and then POOF up they start again. I grab my jacket and cover the flame's. Fire goes out. The "other" couple of extinquishers are not available so too speak. Placed on the other side of the event. I had one shot. Then it be GET OFF THE BOAT.
So yup stuff happens fast. Turns out both shafts stayed in but a trans was fractured. The trans fluid sprayed over the engine compartment and onto the hot section of a head / exhaust manifold. Resulting in a fire as soon as I gave it nice clean air.
Any way the bayliner had an auto halon that I clearly remember going off. Oh that smell, however they do not remove heat like water. So that system was a non event.
Interesting stuff FROM A DISTANCE
But that all being said being there for a guy on the water with a fire on board is just one of them moments. You allowed him to step to saftey not have to climb up outa water or ? Dam nice of you ! hope your around when I need
Yet there is a personal risk we assume when doing such that lots simply can not afford.