yes it is the steel hull we are protecting..just a thought as i saw one in a 6oft steel boats putting anti-fouling paints in their propellers aside from a few zinc anodes in their hulls.they claim it lessen corrosion effect due to dissimilar metal in water and coating the propeller avoids marine growth....just the same i think electrical contact exist and has probably an effect on propeller efficiency as these are not a common practise...but i have no experience on how to do protect the boats hull using electrical current..thank for the reply cloa..