This "professionally installed" alternator replacement was anything but professional. The new alternator had a 1/2" pulley yet this engine uses a 3/8" belt.... Can you say engine choking belt dust....
How any technician could walk away from a boat like this is beyond me. According to the owner at least two yards, beyond the original install, had looked at this and none solved the problem. Sad really because the issue is SO obvious. One look at where the belt sits in the alternator pulley vs. the crank and water pump pulleys and it becomes painfully obvious....