July 13, 2016

The magic of the centerboard

I OFTEN THINK what a clever invention the humble centerboard is. In some ways, it’s the equivalent of a wing on a plane, but on a boat it’s a mostly invisible part of the magic of sailing.

I say magic, because the centerboard, like a fin keel, stops a boat making leeway by making leeway. That’s right. If a centerboard didn’t make leeway of between 3 and 5 degrees, it couldn’t work. It wouldn’t provide the “lift” to stop a sailboat drifting off to leeward so fast on the beat that it would never be able to make way to windward. And it has to be moving forward through the water to provide lift, of course, otherwise it will be stalled and allow the boat to slide sideways.

According to The Oxford Companion to Ships and the Sea, the centerboard for small craft was invented in America in colonial times. “The need to be able to sail to windward close-hauled, with an entirely flat-bottomed work boat arose from the great stretches of shallow waters found in the Chesapeake Bay and along the Atlantic seaboard from Long Island Sound to Florida, and so the centerboard was born.”

Although some famously successful ocean racing yachts have had centerboards, naval architect Ted Brewer says the pure centerboard cruiser has fallen out of favor now, although it still has much to offer the sailor.

If you’ve sailed with a pivoting centerboard, you’ll know how useful it is in balancing the helm by moving the center of lateral resistance forward and aft. If you raise the board partly to angle it aft, for instance, it greatly reduces the tendency of a sailboat to round up while on the dead run.

To take this a step further, some boats have two centerboards, one large one up forward, and another smaller one aft. The task of the forward board is to reduce leeway, while the aftermost board is raised or lowered to attain neutral helm. This is particularly handy in heavy weather, when the changes to sail balance caused by reefing can by compensated for by adjusting the boards.

Like a fin keel, the efficiency of a centerboard usually increases with its aspect ratio. The longer and thinner it is, within reason, the better it will perform, especially if it is given a streamlined shape that provides more lift for its area.

It seems so simple when you look at it. You simply stick this piece of board down into the water through a slot in the boat and it stops you going sideways. But if you care to think about it, there’s a lot of interesting science and hydrodynamics going on down there. Like many aspects of sailing, we don’t normally give it much thought. It just works when we want it to, and that’s that. But it’s magic all the same.

Today’s Thought
 ‘Tis frivolous to fix pedantically the date of particular inventions. They have all been invented over and over fifty times. Man is the arch machine, of which all these shifts drawn from himself are toy models.
— Emerson, Conduct of Life

“What happened to that guy who tried to cash your check?”
“They took him away in a strait jacket.”

No comments: