The voltage of the direct current, appears in abbreviated form as Vcc (Volt Continuous Current) or from the English Volt Direct Current as Vdc.
In boats it consists of the downstream line of batteries, which passes through the battery breaker and then arrives at the electrical panel in the part dedicated to 12 Vdc devices and then also to electronic instruments.
In boats it is therefore widely used by several devices specially designed with this standard, also because it is the only one that can be used during navigation when you do not have a generator or inverter.