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Ask Sail: Centerboard Corrosion

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David Soule of Gardnerville, Nevada, asks:

I recently removed the centerboard from my 1978 Balboa 21 to work on the pivot pin. The board is a 2ft x 4ft half-inch steel plate and has some minor rust. After I fix the pin and remove the rust, what product do you recommend to protect the steel before I reinstall the board? The boat is sailed in both fresh and salt water, and is stored on its trailer.

Don Casey replies:

If the centerboard is galvanized and exhibits only minor rusting, I would just hit the rust spots with a  so-called “cold galvanizing” zinc-loaded spray paint. You may need to treat fresh rust spots annually. If the centerboard is bare steel and shows only minor rusting after more than three decades, I might be inclined to leave the board bare, unless you plan on using the boat differently.

To eliminate all surface rust, the best choice is an epoxy barrier coat. Apply the initial coat of epoxy immediately after the metal has been sanded bright, then wire brush the metal through the wet epoxy. This ensures that the epoxy will adhere to the metal. If using epoxy resin rather than a commercial barrier coat, you need to eliminate air bubbles and force the resin into the grain of the steel. Take a third of a foam roller split lengthwise and drag it across the wet epoxy like a squeegee. You should treat only one side of the board at a time and perhaps divide each side into smaller sections. Treat whatever area you can cover with a single mixed pot of epoxy before it begins to gel. Add additional coats until you get a dry film thickness close to 20 mils. This is typically six or seven coats.

After the epoxy has cured for at least a couple of weeks, you can scrub it with water and a Scotchbrite pad to remove the waxy surface blush. Scuff it lightly with 100-grit paper and paint it with whatever bottom paint you like—antifouling or otherwise.

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