Here is a photo of Olympic's center propeller area. The light colored object is a zinc sacrificial anode plate applied to the sternpost. Above it is a smaller rectangular zinc plate. Additionally there were narrow zinc strips applied to the forward end of the rudder. What you really can't see clearly in this photo is that on the upper and lower surfaces of the center propeller aperture, a narrow zinc strip was applied. This was the extent of the sacrificial zinc anodes which were applied.
View attachment 49641