How do sail boats actually work?

Question

The sails always seems to be somewhat parallel to the direction of the boat, but if the wind is blowing sideways, should that push the boat off course?

In: 9

Answer 1

The next time you’re at a pool, grab one of those floaty board things, shove it deep underwater, and try to wiggle it around.

You’ll notice that it’s really easy to move the board along its thin directions, but really hard to move it along the flat, wide direction.

Sailboats (and most other boats actually) are like that board. They have long thin underwater bits that make it very hard for them to be pushed sideways.

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Another fun thing about sailboats is that the most intuitive way for them to work, with the wind pushing directly into back of the sail to move it forwards, is actually the slowest way to sail.

The fastest sailing is when you’re travelling directly perpendicular to the wind.

The reason for this is that (modern) sailboats use their sails as *wings* instead of like parachutes.

The wind pushes the sail into a nice curved shape, just like the wing of a plane. Then the pressure differential between the outwardly curved and inwardly curved sides is what pushes the sailboat forwards.

This is what allows sailboats to sail upwind. The wind is *pushing* them back, but the pressure difference across the sail makes the boat move forwards anyway.

Answer 2

The next time you’re at a pool, grab one of those floaty board things, shove it deep underwater, and try to wiggle it around.

You’ll notice that it’s really easy to move the board along its thin directions, but really hard to move it along the flat, wide direction.

Sailboats (and most other boats actually) are like that board. They have long thin underwater bits that make it very hard for them to be pushed sideways.

___

Another fun thing about sailboats is that the most intuitive way for them to work, with the wind pushing directly into back of the sail to move it forwards, is actually the slowest way to sail.

The fastest sailing is when you’re travelling directly perpendicular to the wind.

The reason for this is that (modern) sailboats use their sails as *wings* instead of like parachutes.

The wind pushes the sail into a nice curved shape, just like the wing of a plane. Then the pressure differential between the outwardly curved and inwardly curved sides is what pushes the sailboat forwards.

This is what allows sailboats to sail upwind. The wind is *pushing* them back, but the pressure difference across the sail makes the boat move forwards anyway.