B is fine if you don't recharge at the dock from a deep discharge. Charging will take a VERY long time. When working at a utility we only used float charging for our station battery banks - 48 to 230 VDC. We did maintain them regularly, reading each cell voltage, etc, and equalized when necessary to avoid cell reversing. That's a problem we don't have with 12 volt batteries.
A is what is normally used by sailors to provide faster charging.
The charger should also be adjusted for the battery's temperature. There is a switch on your charger for that if you use A.