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

It’s like a toy car on a string.

In the water, there’s a few fins that work like the tires of the toy car. Above the water, there’s wind that works like somebody pulling the string.

It’s not an exact comparison, but this is ELI5.

When the string is pulled, the car wants to roll in the direction of the tires, not always directly towards the person pulling the string.

The tires can turn much like the rudder of the boat to steer.

Beyond this, things can become slightly more complex when sailing perpendicular to the wind or towards where the wind is blowing from. (But not directly into the wind, that doesn’t work.)

This is where the angle of the sail becomes quite important. The force of the wind acting on the sails and the force of water acting on the fins can squeeze the boat (in a sense).

Like pinching a bead in your fingertips, the bead can be launched away while neither of your fingers are applying force in the launch direction. It’s two separate forces working together to create a new force in a different direction.

Answer 2

It’s like a toy car on a string.

In the water, there’s a few fins that work like the tires of the toy car. Above the water, there’s wind that works like somebody pulling the string.

It’s not an exact comparison, but this is ELI5.

When the string is pulled, the car wants to roll in the direction of the tires, not always directly towards the person pulling the string.

The tires can turn much like the rudder of the boat to steer.

Beyond this, things can become slightly more complex when sailing perpendicular to the wind or towards where the wind is blowing from. (But not directly into the wind, that doesn’t work.)

This is where the angle of the sail becomes quite important. The force of the wind acting on the sails and the force of water acting on the fins can squeeze the boat (in a sense).

Like pinching a bead in your fingertips, the bead can be launched away while neither of your fingers are applying force in the launch direction. It’s two separate forces working together to create a new force in a different direction.