[Jomatra]

We have a 2000 35' Open with 370HP Cummins. Everything was fine until a week ago when I started the engines the port gage (engine bank) showed 11V and starboard gage (house bank) read 11.5V (this .5 deviation is normal only about 1.5V low) I took a reading directly from both banks and the both read 12.5V (engines running).I decided to take it out for a short run and after a short period of time the voltage increased to normal readings on the gages. Today I started the port engine and reading on the gage was normal, when I started the starboard engine both gages went to the previous low reading of 11V and 11.5. I once again took it out for about 2 hours (constantly monitoring the status of the batteries) and this time it did not return to normal. With the engines still running at the dock, I once again checked the banks and they both were 12.45V. It seems strange to me that both alternators would give me trouble at the same time. Is there a voltage regulator that works both engines. Any suggestions, advice, or comments would be appreciated.