How a Sacrificial Anode Protects a Boat

Choose the boat hull metal and the attached anode metal. The more active metal loses electrons first, so it corrodes instead of the boat hull.

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Boat hull metal Steel / iron hull Aluminum hull Copper alloy part

Attached anode metal Magnesium anode Zinc anode Aluminum anode Iron anode Copper anode

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Reset anode

Protection statusProtected

Metal oxidizedZn

Electron directionAnode → hull

Anode remaining100%

electron, e⁻ metal ion dissolved O₂ OH⁻ forms near hull

Metal connected underwater in salty water

Salt water completes the circuit by allowing ions to move.

Hull: Fe is protected

Anode: Zn atoms become Zn²⁺ ions

e⁻ flow to hull

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−

−

−

−

Zn²⁺

Zn²⁺

Zn²⁺

Zn²⁺

O₂

O₂

O₂

OH⁻

OH⁻

OH⁻

At the sacrificial anode

Zn → Zn²⁺ + 2e⁻

Zinc atoms lose electrons and enter the water as ions. This is oxidation.

At the protected hull

O₂ + 2H₂O + 4e⁻ → 4OH⁻

Electrons arriving at the hull are used in a reduction reaction, so the hull metal is less likely to lose its own electrons.

What students should notice

1. The anode is more active

A sacrificial anode must be easier to oxidize than the boat metal. Magnesium, zinc, or aluminum can protect steel because they lose electrons more readily.

2. Electrons protect the hull

The anode sends electrons through the metal connection to the hull. Those electrons make it harder for hull atoms to become positive ions.

3. The anode is used up

The anode corrodes on purpose. It must be inspected and replaced because it slowly dissolves into the water as metal ions.