Why Ship Chains Are Studded With Giant Iron Nubs

If you peer over the side of a cargo ship as it lowers its anchor, you'll spot a heavy chain dropping toward the water. The links are thick, some as big as your forearm, and each one shows off a rugged design built for work. But if you watch carefully, you'll notice something unexpected: every so often a link swells with an iron bulge, or sits next to a pair of odd, paw-shaped projections. These aren't flaws or hasty repairs. They're 'stud links' and 'kenter shackles,' inventions honed over hundreds of years to fix a problem most people never notice.

Ships need hundreds of meters of chain to be sure the anchor will hit the seabed. If that chain kinks or ties itself in a knot, a ship can be stranded, sometimes in the worst conditions. Chains with plain round links, the kind you'd find around town, will twist and wrap on themselves under stress from ocean currents and swinging hulls. Once these links lock up in a steel snarl, untangling them becomes nearly impossible, and in a storm, the consequences can be dire for the crew.

That's why the stud link was created. Here, a solid iron stud is welded across the inside of each link. It stiffens the link against crushing forces and blocks the chain from twisting or bending out of shape. The result is a chain that's stronger throughout its length, and far less likely to jam or knot as it's hauled up, even when the ship rolls and the anchor swings.

Kenter shackles are another odd feature you might spy. These oversized, detachable links stand out with their flat sides and hefty center bolts. Crews use them to quickly swap out damaged chain sections at sea. They're also painted or notched at regular intervals, working as depth markers so officers can track how much chain is out, even in darkness or bad weather.

So next time you're near a docked ship, try to catch a glimpse of the anchor chain. Its details tell a story of how seafarers have learned to outsmart the ocean, link by link.