the physics of sailing

February 21, 2008 at 7:39 pm | | journal club, science@home

physics-today.jpgThe cover story of February’s issue of Physics Today, the publication of the American Institute of Physics, is the physics of sailing. I like sailing: grew up on the coast of Maine sailing Lasers—and eventually and Ensign—every summer. Obviously, I can’t afford to sail out here in San Francisco, but I get to go home every summer and sail in Casco Bay.

I thought the cover of Physics Today was a little cruel: “Hey you, in that dark laser lab, check out what these smart people are doing: Sailing!” But the article was actually pretty cool. The basic stuff was in there, and it even had equations (like Reynolds number). But really, I just looked at the figures.


This is a helpful one: you can go faster on a beam reach than when running downwind. If you don’t realize that a (modern) sailboat is wings on the water, going directly downwind is what you would intuitively want to do. And going upwind is mind-boggling.

But my favorite figure was this image of sailboats racing in the fog:


The beauty of vortices trailing off in the fog for thousands of feet was stunning. I also like that you can see that the third boat from the top is tacking and temporarily interrupting the trail. Cool.

Well, here’s a PDF of the article if you’re interested.


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  1. Are you sure you weren’t sailing on an optical maser?

    Comment by Mike — February 22, 2008 #

  2. i get it.

    Comment by sam — February 22, 2008 #

  3. But first let’s start with the downwind case. If the sailor wants to travel in the same direction as the wind, then all he or she has to do is hold the sail perpendicular to the wind and let the boat be pushed from behind. This is the most basic point of sail, and wasoften used by ancient Egyptian, Greek, and Roman sailors. When they needed additional speed or wanted to travel upwind, they rowed. The large square-rigged boats popular in the h and h centuries (the classic pirate ship, for instance) were also most effective on a downwind sail. Modern sailboats can sail in any direction that is greater than about 45 degrees with respect to the wind. They can’t sail exactly upwind but with a clever boat design, a well-positioned sail, and the patience to zig-zag back and forth, sailors can travel anywhere. To explore this, let’s draw a diagram that labels all the forces on the sailboat. If you haven’t seen a force diagram before, not to worry it’s just a few arrows and triangles. By adding the forces together we will get the total force on the boat and thus the direction in which it will move. Here’s a basic sailboat. The two parts we will focus on are the sail above the boat and the keel below the boat. The keel keeps the boat from tipping over and, as we shall see, plays a crucial role in moving the boat forward.

    Comment by young — November 9, 2019 #

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