Metals have different electrochemical potentials when in contact with one another and form Galvanic cells. The metal with a lower potential in the galvanic cell will be anodic and will corrode. The same effect can occur in areas of different electrochemical potential in a single piece of metal such as a steel plate. Any craft moored and operating in fresh, salt or brackish water is at risk from corrosion and the effects can be costly.
A clean hull can save you about 30% of fuel bills; it is common knowledge that fouling on the boat’s hull, will lead to increased resistance, which basically means you are going to burn more fuel for every knot you make.