Corrosion happens in the presence of a conductive medium like salt water and two dissimilar materials which are in very close proximity of, or even in contact with each other.  Such an arrangement essentially forms a battery with one of the two materials acting as the anode and the other acting as the cathode of the battery.  The anode material is the one of concern as it will corrode.

Stainless steel and aluminum exposed to saltwater form one such battery.  In this case, aluminum is the anode and corrodes.  The bigger the contact area between the two materials, the faster the corrosion progresses.  The speed of corrosion further increases if the stainless steel (cathode) mass near the contact area is large compared to the one of the aluminum (anode).  That is why backstays corrode typically faster near the pin than at the hull, even though stainless steel hardware is used at both places.

Some of the other factors which can speed up the rate of corrosion are design features trapping saltwater, humid air which will keep salt deposits moist and the thoroughness of regular boat maintenance.

The corrosion of an aluminum part can be delayed, slowed or maybe even stopped by “coating” it with an inert layer.  This can be done with paint, some plastic coating or a chemical process called anodizing.  If the inert coating gets damaged, e.g. by screws, tools, split lock washer, etc., corrosion will start where the aluminum is exposed.

Starting points for corrosion can also be pin hole sized “holes” in the coating.  A piece of metal can even corrode on its own if it contains any impurities on its surface and hence forms an “internal” battery between that impurity and its base metal.

If the aluminum part has been bent or is constantly worked (during a rowing stroke) near the contact area with stainless steel, the built in stresses open the aluminum to yet another form of corrosion.  This so called stress corrosion will lead to cracks along stress lines and to a premature failure of the aluminum part.

Typically, anodizing and especially hard anodizing (the inert protective layer is much thicker than for standard anodizing) an aluminum part is sufficient protection for rowing in fresh water.  It is even fine for rowing in most salt waters if combined with rigorous maintenance and cleaning.

However the only way to really stop any corrosion between the stainless pin and the backstay when rowing in salt water, is to eliminate aluminum at the pin area altogether – hence the stainless steel pin connector option for Powerlink backstays.  In this case the salinity level of the salt water doesn’t matter.  Glass reinforced Nylon bushings safely insulate the stainless pin connectors from the aluminum tubing of the Powerlink backstays.