[Silver Rush]

I have a 1997 3100 open with 454's. Here in the great lakes we troll at very low speeds (i.e. 1.8 to 2.8 mph). In order to do that I run one engine at a time. When I use the port engine my volts stay between 12 and 13 but when I use the starboard engine the volts slowly drop, the last time it was down to a little less then 11. When I raise the RPMS to over 1000 it begins to slowly rise. I am thinking it is the alternator, is there an easy way to check it? Could it be some sort of regulator that is not working properly. Any suggestions? 

The 31 open has Balmar alternators with separate Balmar voltage regulators,designed for 4 stage charging in a cruising environment. I have a 96 open with the 454s and had bad regulators when i bout it an one bad alternator. I could have had everything rebuilt but I too troll lake Michigan. I opted to replace both alternators with new Balmar alternators with smaller pulleys and internal regulators. Now i get great charge for all my systems while trolling.