Why Boats Need Zinc
Why Boats Need Zinc: A Beginner’s Guide to Cathodic Protection
Corrosion is one of the biggest enemies of any boat, especially motor yachts with complex systems and powerful engines.
To fight it, boaters rely on sacrificial anodes, often made of zinc.
This blog explains how zinc protects your boat, where to install it, and how to maintain it—so even a beginner can keep their yacht in top shape.
What Is Galvanic Corrosion?
When two different metals are underwater, an electrical current flows between them.
This causes the less noble metal to corrode faster.
Saltwater speeds up this reaction because it’s a great electrolyte.
Without protection, critical components like shafts, propellers, and heat exchangers will corrode.
How Zinc Anodes Work
Zinc is more reactive than most other metals used in marine systems.
When connected to less reactive metals (like bronze or stainless steel), zinc corrodes first.
It “sacrifices” itself to protect more valuable parts.
This is called cathodic protection.
It’s a simple and reliable method to stop corrosion before it starts.
Why It Matters More on Motor Yachts
Motor yachts have more underwater metal and electrical systems:
Twin propeller shafts
Large trim tabs
Hydraulic platforms
Stern drives / pods
Seawater-cooled engines and generators
Each one is a potential corrosion point.
Motor yachts also tend to stay plugged into shore power, which increases the risk of stray current corrosion—making zinc protection even more critical.
Where to Install Zinc on a Motor Yacht
Key areas to protect include:
Propeller shafts – Shaft zincs are clamped near the prop
Rudders – Plate zincs bolted directly on
Trim tabs – Small disc or plate zincs
Transom – Large zinc blocks or plates
Engines / heat exchangers – Internal pencil zincs screwed into housings
Bow and stern thrusters – Anodes fitted to housings or prop blades
Stabilizers or hydraulic parts – Where applicable
Make sure each anode has solid metal-to-metal contact.
When and How to Replace Zinc Anodes
Check your anodes regularly—especially during:
Haul-outs
Diving inspections
Routine servicing
Replace anodes when:
They’re more than 50% consumed
You see deep pitting or flaking
They’re loose or cracked
Note: Don’t paint over zincs. Paint blocks the electrical flow and renders them useless.
Zinc, Aluminum, or Magnesium?
Choose based on your boating environment:
Zinc – Saltwater only
Aluminum – Salt or brackish water, longer lasting
Magnesium – Freshwater only (too reactive for saltwater)
For motor yachts that travel between different regions, aluminum is often the most versatile choice.
Bonus Tips for Motor Yacht Owners
Use a bonding system to link all underwater metals to the anodes.
Always match anode material across the boat. Don’t mix zinc, aluminum, and magnesium.
Add a galvanic isolator to shore power to reduce corrosion risk.
Monitor anodes after any electrical work—changes in wiring can impact effectiveness.
Final Word
Zinc anodes are your first line of defense against marine corrosion.
For motor yachts, where the systems are more complex and the stakes are higher, proper use of sacrificial anodes is essential.
Routine checks, proper placement, and timely replacement will save you from costly damage.
Let the zinc wear out—not your yacht.