That is possibly / probably your earthing plate - not an Anode. It wou;dn't be much pont having an earthing plate that eroded away.
3.1
craft’s ground/earth
protective grounding connection, provided for safety purposes, that is established by a conducting connection with the common ground/earth (potential of the earth's surface)
3.4
main grounding earthing point
main point that provides connection for the DC negative conductor, AC protective grounding conductor (3.10) and bonding conductor to the craft's ground that is established by a conducting connection (intended or accidental) with the common ground (potential of the earth's surface)
Note 1 to entry: It can include any conductive part of the wetted surface of the hull in permanent contact with the water, depending on the overall system design.
6.2
For craft having a fully insulated DC system, the AC protective conductor shall be connected to:
a) for metallic hulled craft, the hull;
b) for non-conductive hulls, the craft's external ground/earth or ground plate.