Ever wonder how a sailboat sails into the wind? Or why, as you build speed, you can point closer to the breeze?
When under sail there are a number of different forces that effect your speed and direction of travel. The wind and water both create forces on your yacht, keel and sails; all of these combine together to determine your speed and direction of travel.
So, how does a boat sail into the wind?
The way sails work while sailing upwind is very similar to how an aeroplane wing works.
The curve of the sails means the wind has to travel a longer distance over the outside (front) of the sail, creating a low-pressure zone. The shorter distance the wind travels on the inside of the curve (back) creates a relatively high-pressure zone. This imbalance in pressure is what makes the yacht move, as it is perpetually pulled towards the low-pressure zone.
If this was the only force effecting a yacht, it would move sideways instead of in the desired forward direction.
Luckily, the water you’re sailing in also produces forces against the keel and hull of the yacht that help to keep you moving forward.
As the wind pulls the yacht one way, the water produces an opposite force against the hull and keel of the yacht, pushing it in the other direction.
The vector forces of the sails and hull/keel together produce the total force that propels the yacht forward (and slightly sideways) through the water.
This is a very simplified explanation of some of the key forces that allow a boat to sail forward. If you’d like to do some further reading, check out these resources:
- Physics Central – The Physics of Sailing: How Does a Sailboat Move Upwind?
- University NSW – The Physics of Sailing
- North Sails – How Sails Work
- Stanford Yacht Research – An Explanation of Sail Flow Analysis