[Medicone]

I heard of similar issues with the 8.1s.  At least on my (previous) 8.1s, the alternators have external voltage regulators (Charles C-Charger double alternator regulator) that controls the output to the battery banks.  I watched some videos of another Tiara Open with 8.1s running and the voltage gauges were as you described (low voltage on one or both banks).  I don't know if the gauges monitor alternator output or battery charge level.

While you are underway (obviously with someone at the helm), check the voltage readings on both battery banks (house/engine) on the DC panel inside the cabin.  You will probably notice that they indicate that the proper charger voltage is being supplied, even though the gauges on the helm indicate otherwise.  In my experience, the charge didn't kick in until around 1K rpms.

Also, not sure if you have gel or lead acid batteries, but you may want to check the Charles C-Chargers to make sure that the dip switches are set to the proper battery type, which changes the charge profiles.

Best of luck!

M1