How to Harness the Wind (Crossing the Wind I)

Sailing is a prime form of technological magic that we take for granted. You stick a boat in the water with a standing sheet of cloth or plastic and expect it to start zooming wherever you like. Pretty miraculous, though. Like flying, it’s not just going fast and having wings, but how the wings are shaped. In the same way, sailboats move because of how the sails are shaped, and how they’re allowed to move.

Phoenician ship
Phoenician ships ruled the Mediterranean 3000 years ago, photo by Jennie Hill

Human cultures have a lot of coastlines, so for eight millennia, those cultures learned how to navigate long distances–without computers, electricity, steam power, sextants, or even nails. The Portugese, Phoenicians, Vikings, and the Chinese all created distinct seafaring dynasties, each in their own turn. As I’m about to start a journey across the Atlantic on a boat, I decided to try to understand exactly how they did it.

If Square, Add Oars

The oldest known ship, the Pessoe canoe in the Netherlands, dates back to 8000 BC. From Easter Island to the fertile crescent to the Inuit, people have been hollowing out a tree or lashing logs together, raft-like, in order to move across the water. Many added a bit of cloth mounted on a stick to move away from the wind, plus some oar power to keep going when the wind was in the wrong direction or nonexistent. Early depictions of the sails in the cradle of civilization near the Mediterranean were square, dating back to Egyptian hieroglyphs. The Vikings slimmed the ships, but added lots of oars. Columbus gets credit for sailing from southern Europe over to the southern mid-Atlantic, but other accounts have Leif Ericson finding the northern North American coast much earlier, and St. Brendan possibly going from Norway to Newfoundland before the first millennium. The Ericson ship model was, in fact, reconstructed in the 1920s and sailed again from Europe, eventually ending up into Duluth, where it has been refurbished and stands in a park today.

Leif Ericson ship reproduction
Leif Ericson ship, sailing to Duluth. Photo by Tom Kasper, 1927

The Vikings didn’t change the basic sail design, but they did add a few other technology advances. Viking ships were narrow and long, with a comparatively shallow base that allowed it to sail in very shallow waters. Ships were symmetrical, which allowed them to be reversed easily in case they needed to back out, for example, if they reached an impenetrable ice sheet. They were light enough to be transported over land as needed, easy to imagine in lands striped with rivers and sandbars. Warships were long to hold lots of warriors, who doubled as oarsmen to gain the speed they needed to mount quick, lethal attacks. But the next big advancement for ships–the one that launched the Age of Discovery in Europe–was the triangular sail.

Maori waka ship with triangular sail, photo at

The Persians and the Maoris Had It

Historians say that the lateen sail launched the Age of Discovery, when the Portugese, Dutch, and Scandinavian traders started going across all the ponds. Of course, the triangular sails might have been in long use along the Nile, in the Indian Ocean, and in Polynesia for centuries, so “invented” is a dubious term. Wherever they came from, once the growing merchant cultures had them, exploring and trading was on. They created the speedy caravel which anyone who ever played Civilization knows quite well.

The Nina with lateen sails. Photo at

Columbus used a core caravel design for both the Nina and the Pinta, using the bigger, partly square-sailed carrack for the Santa Maria. Ships also had, by then, added more of a keel and put a steering rudder in the back. What is it about that triangle version that made it so much more useful for sailing?

Acting as “I” beams, they resist the forces on the sail that try to compress the leech in towards the luff when the sail is sheeted in. This preserves the open leeched airfoil shape and keeps the sail from becoming fuller and more semicircular (rounded leech) as the breeze and the loads increase. A flatter airfoil shape with a straight, open leech keeps the boat upright and reduces weather helm. The more roach you need to support, the greater the compression, and the more important battens become. from

Luffing your Lateen until the Leech

Triangles are where the rubber meets the road, or where the wind hits the fan, so to speak. Of course, as soon as you start trying to understand the Physics of sailing, the terminology goes quickly over your head. This is especially true if you’re a modern sailor trying to understand a modern boat–I got quickly towed under by the leeches and the luffs. The sailors reading this are raising an eyebrows, so forgive me if I get it wrong… the lateen means triangle. The luff is the straight part, attached to the vertical mast, and the leech is the back “round” part.If you’ve ever tried to sail, you probably know that when you want to sail into the wind, you move in a zigzag pattern, at a 45 degree angle. I always thought that tacking simply meant the wind was moving you from the side, but it’s more complicated than that. Yes, my physics son, vectors are involved.

Sailing physics

The Physics of Sailing Photo from

The wind comes it and hits the sail at an angle, so the boat is prompted to move. But if it’s properly held fast, the boat will move at the angle and slightly forward. However, if the wind is strong, the boat would normally just move sideways, except for the keel. A deep keel will face resistance from the water, which prevents the boat from going sideways, and instead it goes forward-ish.

Tall triangle sails

Tall and triangular at the America’s Cup 2013 in the Golden Gate. Photo by Abner Kingman

When the sail is tall, the wind at the bottom is also directed upward and catches as much of the sail that’s there. Plus airfoils shape, that’s spreading air pressure in that complex way that works on planes and more and more vectors, Victor.

Interestingly enough, the Chinese did not use keels. Instead, their boats–the Chinese junks–had flat-bottoms. But their technology was sophisticated for a variety of other reasons.

The Battens–the Chinese, like Aristotle, Seemed to Know Everything

Chinese junks came in a huge variety of sizes, everything from a single sail to move through along the myriad rivers, to multiple sails for trading. Flat bottoms were used, but the Chinese made use of a stern rudder for steering, long before the Europeans did. The rudders acted both to steer and as a keel for moving upwind.

Sails on the Chinese ships were also placed oblique to the wind and curved to take the best advantage of the wind, including directing the wind more effectively from the front one to the those in the back. Chinese sailors also derived ways to create water-tight compartments–bulkheads–which helped with flotation and speed. And they used battens.

Chinese junk

Chinese junk, obligue, battened sails. Photo by brighthub engineering

You probably know the expression “batten down the hatches,” and you probably know that has something to do with securing things. I, foolishly, thought it meant tie down the cargo, but not exactly. A batten a strip of wood or inflexible material. To batten the hatches is to use nailed battens over tarps to cover the hatches to the holds, where cargo or people may be trying to wait out a storm.

Battens are also used on the sails themselves. Today’s sails would have a batten extending from the triangle-part inward, although not necessarily all the way. The batten keeps the material stiff because when you are raising the sail, the extra material will flap around rather hazardously until the sail is all the way up or down. Battening the sail alleviates the problem. Note that the Chinese sails were fully battened, so that raising and lowering them was more akin to Venetian blinds. Overall, the Chinese sails were quick and easy to bring down, or “reef,” as follows:

Naturally curious, I asked the skipper about reefing the junk rig. He had just passed around fresh mugs of hot chocolate, so I expected a brief discourse on the subject. Instead, without saying anything he walked over to the main mast and with one hand released the main halyard just enough to let it slip over the belaying pin, paying out about half of it and then belaying it again. The boat was reefed. He did not put down his mug of hot chocolate… and he did not spill any.

Old Age Crystals and Sunstones

Now, we know how the sails work. Most of us know that they knew where to get to by using the stars and position of the sun. However, the Vikings may have had a different method. After all, quite a bit of the northern climates don’t see the sun for much of the year, and if they don’t see the sun, they also don’t see the stars.

Navigation crystals
Viking crystals may have helped navigation. Photo by Arnien/Wikimedia commons

Recent historians think the Vikings may have spotted the sun by using crystals. Several expeditions have found fairly large partly carved bits of calcite on foundered ships. Speculation is that by using the crystals with very little or diffused light, plus another scientific concept called polarization, to determine what direction the sun is in. But explaining that would require a whole extra blog. I’ll stick with the wind.

We’re off to sail across the Atlantic, then up the west coast of Europe and around the British Isles. Next week: Columbus and the Mayflower–how did that crossing go?

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