What zincs do
Zincs — sacrificial anodes — protect the metal under your boat. In salt water, different metals connected together form a battery, and the most active metal corrodes first. Zinc is more active than bronze, stainless steel or aluminum, so it corrodes instead of your shaft, propeller, drive and through-hulls.
The half-worn rule
A zinc does its job only while there is enough of it. Once it’s about half worn away, it protects less, and the shaft, propeller and drive start to corrode instead. That’s the time to replace it — not when it’s gone.
Why zincs wear fast in Miami
Warm salt water speeds up corrosion. Stray electric current — from shore power, a neighbor’s boat or a fault on your own — can eat a zinc in weeks. That’s why we check zincs at every cleaning and tell you when they’re due.
A zinc that doesn’t wear at all is a warning sign too: it may not be making good electrical contact, and then it protects nothing.
Zinc, aluminum or magnesium
In salt water, use zinc or aluminum anodes. Aluminum also works in brackish water and lasts a little longer. Magnesium is for fresh water only — in salt water it wears away too fast. Stick to one type on the boat, the one your drive or engine maker specifies.
Replacing zincs in the water
Shaft, outdrive, trim tab and rudder zincs are replaced by a diver in the water, at your dock or slip. Engine zincs inside the cooling system are a mechanic’s job. Labor starts at $200 per visit — our minimum for any visit; the zincs are extra, at parts price plus sales tax. Labor isn’t taxed.