How AC/DC Charging works?
AC = alternating current
DC = direct current
Power taken from the grid is always AC because it can transmit over great distances without much loss of power. But to store power in a battery (like in an electric boat), there must be a conversion to DC.
With an AC charger, the conversion takes place inside the boat via the onboard charger. Whereas when you use a DC charging point, the conversion from AC to DC happens within the charging point, thus allowing the DC power to flow directly from the charging point and into the battery. As the conversion process happens within a more spacious charging point and not the boat, larger converters can be used to convert AC power from the grid very quickly.
Another fundamental difference between AC and DC charging is the charging curve shape. In case of AC charging, the power delivered to the boat is simply a flat line. The reason for this is the small size of the onboard charger and, accordingly, its limited power. Meanwhile, DC charging creates a degrading charging curve, as the boat's battery initially accepts a faster flow of energy, but gradually requires less when it reaches maximum capacity.
Which is better AC/DC?
This depends on your situation. If you need a quick charge to continue a long-distance journey, then we'd recommend you would use a high power AQUA DC charge point (if your boat supports it). For any other situation then you would use an AC charger.
Summary
Parameter
AC Charger
DC Charger
Charging current
Provides AC current to on-board charger
Provides DC current directly to batteries
Cost
Relatively cheaper
Higher costs
Charging speed
Usually limited by the capacity of onboard chargers
High charging speed, depends on DC charger