Boat Zincs - What do They Really Do?

We all listen to talk on the docks on the topic of underwater zincs, but what do they truly do? How do they perform?

When you have 2 diverse metals that are physically and electrically linked and immersed in marine water, they establish an electrical flow. Some DC current travels between the two metals which can decay metals such as prop shafts, thru hulls and sea strainers in the engine room.

The best way we can discontinue galvanic corrosion is to attach a piece of metal called a sacrificial anode, and most frequently it is a zinc alloy. In fact, most of us refer to sacrificial anodes merely as zincs. Using zinc anodes on your vessel is very significant. The anode will be used to purposely corrode away sooner than your boat equipment does.

On top of the Galvanic Scale, Zinc is number 4, 1 being the most sacrificial to salt water, Aluminum is 12, Steel is 30, Brass is 51, 316 Stainless is 76 and pure Gold is 91. This is why zinc is used, we wish for it to wear away and guard the other metal in contact with sea water.

Zincs ought to be substituted when about 1/2 of the anode has vanished to corrosion. In an ideal world we want that to take place not more frequently than annually. I check my trawler zincs regularly by diving under the boat and replace those zincs that need it. At haul out, a complete set is always installed. All zincs are not made alike. Insist on MIL spec zincs. There is a dealer on my website Links page that I acquire mine from. High-quality zincs, excellent price.

Props and Rudders

Propellers and prop shafts are more often than not protected by a zinc band bolted together about the shaft. It is essential to make certain the shaft is clean and smooth before clamping the collar to it.

Rudders and struts are also protected with zinc disks bolted diametrically to the metal. Be positive bottom paint does not cover them.

Hull Plates

Hull plates are fastened on the exterior of the hull and are used to bond the boat metals within the boat not directly exposed to salt water.

Bonding is the linking together of zinc plates bolted to the hull to other metals by wires. All of the submerged running gear and the metal inside the engine space is connected to these plates. Be certain you check the bonding between thru-hulls and other metal gear by the use of a multi-meter set on the ohm settings.

Hull plates are typically found underwater on the stern of the boat.

Tip: If you spot "green" bronze equipment, the bonding has failed and deterioration is in development. Check and re-establish the bonding.

Cooling Raw Water

Heat exchangers and engine raw water systems are also at risk. Most heat exchangers are fixed with a zinc "pencil". You will find it under a brass plug. The pencil is unscrewed from the plug for substitution. Additionally, your transmission and oil coolers will be fitted with pencil zincs too.

Mike Dickens, the author, is a boat owner and owner/Broker of Paradise Yachts in Florida USA.

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