1987 Bayliner with a 5.0 shut down in the water. No loud bangs or anything just lost power and shut down. Attempted to restart it and I can hear the starter engage but nothing turns over. Batteries were at 10 volts. I'm guessing something drained the battery, but what would drain the battery? One of the starter wires was hot. I am wondering if I have a short between the two that caused it to drain the batteries. Or could I have spun a berring and it locked up? Or is the altenator shot?