ClimateRight CR-2550 Manuale del Proprietario Scaricare il pdf (Pagina 271)

7-26

CHAPTER 7

Galvanic/Stray Current Corrosion

Metal parts underwater can be subjected to two basic styles of

electrolysis: galvanic corrosion and stray current corrosion. Both can

damage the drive, propeller, underwater parts, boat and motor if not

correctly monitored (testing at 2 week intervals) and avoided.

Galvanic corrosion is an electrochemical reaction between two or

more metals. Drive systems consist of several different metals. Some

are more active than others.

Galvanic corrosion of the more chemically active metals can occur

whenever two or more dissimilar metals that are “grounded” (connected

by actually touching each other, or through a wire or metal part) are

immersed in a conductive solution (any material that can conduct

electricity). Anything but pure water is conductive. Saltwater, fresh

water with a high mineral content and polluted freshwater are highly

conductive. Conductivity increases with temperature. That is why

Florida boats experience more corrosion than boats in Maine.

Speciﬁ cally look at a typical marine drive unit with a stainless steel

propeller. The aluminum is the more chemically active metal (called

the anode) and the stainless steel propeller is the less chemically active

metal (called the cathode).

CORROSION TABLE

Gold

Stainless Steel

Bronze

Copper

Brass

Steel

Aluminum

Zinc

Magnesium

Least Active

Most Active