General rule of thumb 20amps per hour at 24 volts. However there are a number of variables.
Number of crew members.My figures are based on two people on board.
Wind strength and sea conditions determine power required for the autopilot.
Charging only with the Onan approximately five hours in twenty four.
Which all equates neatly to the power available in your battery bank in my case 650 amps at 24 volts giving me a little reserve.
These are very general figures and can alter considerably depending where you are sailing.
e.g. cooler latitudes , more heat required, lower fresh water production from the water maker etc all require more power.
Seafever of Cuan
SM 425 Redline