Wednesday, March 24, 2010


Sailors think they understand the wind, but they don't.

You can't see wind. All you can see is the effect on other things. You look at the ripples on the water, your sail, flags, smoke, etc. etc. and you think you understand what the wind is doing, but you don't.

I discovered this strange fact this weekend. My grandchildren came to our house for the weekend so I skipped sailing on Sunday and played with them. And that's when it dawned on me that I had been totally wrong about wind all the time I had been sailing.

Sailors will say things like, "The wind is 10-12 knots from a direction of 135 degrees." There are several assumptions in a statement like that. It implies that there is such a thing as an average wind range and that it is relatively constant in direction. There is a more subtle implication that the wind can be imagined as a horizontal two-dimensional vector.

That's how we think of it when we are sailing. Sure we know that the wind might vary in direction and speed over time, and at various places around the race course. And we might also know that if we sail a boat with a very tall mast that the wind speed may well be stronger and from a slightly different direction higher up.
But we generally think that at any given time and place it has a certain direction and speed, that can be described in a sentence like the one above.

We are wrong.

I learned this while playing with my 4-year-old granddaughter last weekend. One of her favorite things right now is blowing bubbles. I was assigned the job of catching as many bubbles as I could.

When you watch soap bubbles floating in the air you quickly realize that sailors' assumptions about the wind are all wrong. There is no meaningful consistent wind direction. It changes every second. It changes in a few inches. There are vertical, upwards and downwards, components to the wind. Even bubbles that start at the same place within a fraction of a second of each other will be swirled by the wind at different speeds and different directions and to different heights.

Wind is millions and millions of air molecules jiggling and tumbling around and bouncing off each other and into objects like sails and balloons and this molecule here doesn't really care what that molecule three feet away was doing two seconds ago, and certainly doesn't feel much compunction to behave in the same way as it. Wind is quite a random phenomenon.

I don't think I will ever see wind the same way again. On SailX it is a two dimensional vector at any given point and time. In the real world... not so much. It changes from inch to inch and from second to second.

How strange!

If I think like this when I am sailing it could drive me nuts.


Sam Chapin said...

The "air layer" is 5 to 7 miles thick and you are just bubbling in the bottom 3 or 4 feet.

O Docker said...

A popular tourist activity in the Napa Valley, north of San Francisco, is hot-air ballooning.

We did this once and were amazed to learn that the pilot could take us a few miles up the valley and return us nearly to where we took off by controlling altitude. The wind blew predictably one way near the ground, but in the opposite direction a few hundred feet higher.

Maybe with a tall enough mast, you could sail a whole race downwind.

Anonymous said...

"Bubbles" convinced me that I don't need to buy those strange books about the wind authored by the Annapolis doctor

michael b said...

Strange thing, O'Dock. You could drift around the world downwind. Imagine.

Carol Anne said...

O Docker, we have the same phenomenon in Albuquerque -- balloonists refer to it as the "Albuquerque Box." They can go up to a certain level, go one way, drop to another level, go the other way, and end up where they started.

Meanwhile, at Elephant Butte, I've always known about the vertical sorts of winds. There will be smooth patches of water, where a casual observer might think there is no wind. That's not necessarily the case; sometimes, there's a major downdraft in those spots.

Baydog said...

I'll comment on a simpler topic. There is no doubt that Aidan is Emily's brother. Cherubic does not do them wonder you bail on Sunday races to be with them.

Anonymous said...

Woooooooo SailX!!!!!!!!!

Post a Comment