What is Sacrificial Anodes?
Sacrificial anodes are pieces of reactive metal mounted on underwater metal components to prevent galvanic corrosion. Common locations include hull zincs, shaft zincs, propeller zincs, rudder zincs, trim tab zincs, and internal engine zincs (heat exchanger pencil anodes, engine block plugs).
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What it is
Sacrificial anodes are pieces of reactive metal mounted on underwater metal components to prevent galvanic corrosion. Common locations include hull zincs, shaft zincs, propeller zincs, rudder zincs, trim tab zincs, and internal engine zincs (heat exchanger pencil anodes, engine block plugs). Anodes prevent destructive corrosion by serving as a more reactive metal that corrodes preferentially, protecting less reactive metals in contact with seawater.
What it does
Anodes prevent destructive corrosion by attracting electrical current flow in seawater caused by dissimilar metals in contact. The anode corrodes instead of your propeller, shaft, rudder, through-hulls and engine components. Properly functioning anodes waste away over months, indicating they are actively protecting other metals and turn white or chalky as they corrode instead of staying silver.
Why it matters
Without adequate anode protection, corrosion can rapidly destroy expensive underwater gear. Internal engine zincs protecting heat exchangers and engine blocks must be monitored closely. A failed engine zinc can allow a heat exchanger tube to corrode, creating cooling system failure and overheating that can destroy an engine. Boats in marinas with shore power connections face accelerated corrosion from stray electrical currents if zincs are depleted.
General Maintenance
Inspect all external anodes at every haul-out. Replace any anode depleted by 50% or more, as effectiveness drops dramatically beyond half-life. Check internal engine anodes every 100 engine hours or annually by removing inspection plugs. Replace when 50% corroded. Clean contact surfaces before installing new anodes ensuring bare metal contact. If anodes show minimal corrosion after a season, investigate for poor electrical bonding, painted contact surfaces, or insufficient grounding. Anodes should show obvious wastage indicating they are working.
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