A friend of mine bought a boat last season and was checking things out before launch this year and noticed the anodes looked brand new. I suggested that they might not be the correct material for fresh water which launched a little debate over a few
The issued was resolved after referencing this site
I would report the possibility of electrolysis occurring in the water and see if laws require the marina to investigate to see if it is happening in the water around you first and if so, then see if the shore power on the docks is the culprit. IF not check with the other boats around for bad shore power cables in the water cracked and if so replace. Also if gen sets running on board that could be a problem there. You could try putting over sacrificial anodes to see if that is happening in the water by your boat first. Water and electricity do not mix.