As you can probably only get about 35-40 usable amps out of a 55 amp alternator
, it will take many hours to charge with the alternator
at anchor--say 3-4 hours a day to replace the typical 100-150 amp-hours daily consumption
. You will need to get the engine revs up to 12-1500 to get the alternator output up. I wouldn't worry too much about glazing the cylinders--the motor
will outlive you if you occasionally run it up under load.
If you already have a genset and a 100 amp charger, it would be preferable to running the main engine at anchor
, but you can also charge with the main engine while motoring.