How Do They Keep Ship Chains from Rusting?

“Six days shalt you do all you are able, the seventh the same and pound on the cable.” This phrase refers to general ship maintenance, including hauling chains out of the chain locker and hitting them with hammers to remove rust. The practice of ‘pounding on the cable’ as it’s called has been a common method for centuries.

Rust Prevention Techniques

Chains, especially those that rarely move during use, can be kept from rusting in various ways. For instance, they can be painted or treated with tar to prevent rust. Chain stays on masts are an example where such protective measures are implemented.

Small Boats and Ship Chains

In smaller vessels like my 32-foot sailboat, the anchor chain is coated with zinc for protection against corrosion. This zinc slowly dissipates, protecting the steel chain, but the protection is not permanent and usually lasts for just a few years. The area of the chain closest to the surface, where it is exposed to both saltwater and air, tends to rust the most. I occasionally repaint my chain, primarily to indicate the length—however, this does not significantly help in reducing rust.

Whenever a significant portion of the chain near the surface is corroded, I cut it away and purchase new chain to connect to the remaining damaged part using a joining link that can be hammered shut and still fits around the windlass. The process of corrosion weakening the chain is not significant for decades, but it can be messy—the rust particles can stain the fiberglass deck if not promptly washed away within a day or two.

Large Ships and Their Chains

On a large ship, the anchor chain is much thicker and more substantial, making corrosion a less significant issue. It primarily affects the surface rather than the bulk of the link where the strength comes from.

Environmental Factors and Corrosion

Despite our best efforts, complete prevention of corrosion is challenging. The harsh marine environment itself is an agent of corrosion. Even if anchors are rarely used, the chain inside the chain locker inside the ship can be quite corroded, at least on the surface.

The only way to give the chains a complete overhaul is during a drydock operation, where the chain is removed from the ship, inspected, descaled, repainted, and all markings refreshed.

Despite the limitations, we do some manual efforts to mitigate rust. One method is to drop the anchor up to the 10th or 11th shackle using a controlled brake. As the anchor hits the deck, the rust can fall off instantly into the water. Another common practice is to manually chip and paint the chain, but we only do this on the parts with shackle markings for easy readability at night.

Conclusion

Despite the challenges posed by the harsh marine environment, several techniques are employed to prevent rust and maintain the integrity of ship chains. These include protective coatings, regular inspections, and meticulous maintenance practices, ensuring the safety and reliability of maritime operations.