This is going to sound like a dumb question but here goes...

My mercury outboard is bolted directly to the aluminum transom, the motor is grounded directly to the battery, so the whole boat is now a ground for the battery. This doesn't seem right to me. Right for a car, but not a boat. Is the motor supposed to be mounted in a way that it is electrically insulated from the boat? I had a red wire short out to the boat seat and almost start a fire. Didn't know that the current would run through the boat back to the battery.

Anyway is this normal? If not, any way to fix it?