[Chris Burkard]

Tachs - Swap them and see if the problem follows the tach or stays with its side. At least you will eliminate a part of the system with this test and make it easier to find the problem.

Batteries and charging - Your vessel was originally set up with Gel Batteries, Bal-Mar alternators and the shore charger was set to charge Gel batteries. Gel batteries and flooded cell batteries are not interchangeable. They require completely different charging cycles. A gel charging system will under charge a flooded cell battery and a flooded cell charging system will cook a gel battery.

The Bal-Mar alternators are designed to charge gel batteries. If you wish to switch to flooded cell batteries, you will either have to change out the Alternators or replace the regulators (most likely less expensive to just go to a traditional alternator) with ones designed to charge flooded cell batteries. The house charger should have a switch on it that would allow you to simply flip a switch depending on what types of batteries you are using.

Did you put Gel batteries in the boat or flooded cell (traditional lead/acid)?

An FYI - AGM batteries, even though they are not a traditional flooded cell can be used in place of flooded cell batteries, but are not a replacement for Gel batteries.