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The hulls of cargo chips are painted copper-coloured for a reason. (Gary Blakeley/Getty Images/Hemera)
The hulls of cargo chips are painted copper-coloured for a reason. (Gary Blakeley/Getty Images/Hemera)


How cargo ships repel unwanted passengers Add to ...

This week, Collected Wisdom takes to the high seas to get the lowdown on a colourful maritime mystery.

The question

Why are the bottoms of cargo-ship hulls painted a copper colour? Peter Simpson of Toronto wants to know.

The answer

It’s simply because the paint contains copper, which is an anti-fouling agent.

“Over time, little critters and plants attach themselves to submerged surfaces,” writes George Fowler of Dartmouth, N.S. “The bottom of a ship is an ideal location because it’s near the surface so there is lots of light for plants and, since the ship moves, dinner is always wafted over the animals that filter nutrients out of the water.”

However, barnacles and other organisms clinging to a ship’s hull increase drag and push up fuel costs. “Copper is a biocide,” Mr. Fowler writes, “and controls the fouling of the hull by poisoning the organisms that try to attach themselves.”

He says copper’s effectiveness in this regard was most strikingly demonstrated by marine archeologist George Bass, who excavated a Bronze Age ship that had sunk off the coast of Turkey more than 3,000 years ago. “The copper cargo splayed out over the wood of the hull when it hit the bottom and actually preserved sections of the hull from marine borers for all these years.”

Sven Johansson of Victoria tells us that, before the days of steel hulls, thin copper sheeting was nailed to the bottoms of wooden ships. “In fact,” he says, “the copper-sheeted wooden clipper ships were the fastest sailing ships.”

Norm Rogers of Toronto adds that, as well as protecting wooden ships from barnacles, the copper sheeting prevented pests such as teredo worms – sometimes called “termites of the sea” – from eating holes in the wood.

Incidentally, CW has discovered that teredo worms are not actually worms, but a form of saltwater clam. Why are they called worms? That’s another maritime mystery.

Further notice

We recently told you that horses and cattle can survive outdoors during frigid Canadian winters because they grow thick winter coats. Turns out there’s more to it than that. It’s also because of their size.

Large animals such as cows have more surface area than smaller animals to radiate away metabolically generated heat, but they also have proportionally more volume (and proportionally more total body mass) to generate heat, explains physicist Dave Hanes of Queen’s University in Kingston.

Consequently, he says, “large grazing animals are very much less threatened by cold weather than one might think, which is why bison and caribou have survived for so many millennia, living through Canadian winters.”

A final word on this from Jan D’Arcy of Ottawa: “Years ago, a horse breeder (who lived just outside Montreal) told me that horses that had been left out to pasture in the winter snows and wind always had healthier foals than the ones that had been sheltered in the barn.”

Help wanted

How long must a homing pigeon live in a location before it adopts that location as its home? Alex Saegert of Vancouver wants to know.

Farm homesteads used to have chickens freely ranging, writes Mike Curtis of Vancouver. They also had cats to catch mice and rats. Why didn’t the cats eat the chickens?

Miriam Pyett of Shields, Sask., asks: Why do some online bill payments take up to two business days to go through? Since the transfer is electronic, why doesn’t it just go through immediately?

Let’s hear from you: If you have the answer to one of these questions (or have a question of your own) send an e-mail to wisdom@globeandmail.com. Please include your location and a daytime phone number.

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