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

Okay, so you’re probably looking at sloop rigged sailboats, they look like this: ⛵️

Now, when they’re heading downwind, they can use a sail called a spinnaker or push the mainsail and jib out to roughly parallel to the boat to go faster. They actually do go perpendicular when the wind is pushing them from behind.

So when going upwind (not straight upwind, typically about 45 degrees off of straight into the wind and the sails are off to an angle that creates better lift, but let’s ignore that for now) the sails SHOULD only push the boat downwind, but there’s a clever way to deal with that: a keel. The keel is a straight board in the water that’s parallel with the boat.

So let’s say wind is coming from the top of your phone, straight down. The sail is parallel with the boat/keel, moving 50 degrees to the left of going straight up, with 90 degrees being straight left. (Draw it out if it helps) There’s a component of force down yes, and that should push the boat back, but there’s a leftward component that is bigger than the down component. So the sailboat will go left more than down/back.

Now remember the keel, it’s in water which has much more friction than air. So the keel helps make the boat move in only two directions, forward or back. So whatever force is pushing on the sail pushed down to the keel, and is equalized out. The only part of the force that is allowed to push the boat forward is the remaining leftward force, which pushes the boat left, but that gets equalized out too by the keel, so the boat slips forward in the keel direction too.

In the end the boat is pushed left, but because of the keel, goes forward and left, along that 50 degree bearing.

Answer 2

Okay, so you’re probably looking at sloop rigged sailboats, they look like this: ⛵️

Now, when they’re heading downwind, they can use a sail called a spinnaker or push the mainsail and jib out to roughly parallel to the boat to go faster. They actually do go perpendicular when the wind is pushing them from behind.

So when going upwind (not straight upwind, typically about 45 degrees off of straight into the wind and the sails are off to an angle that creates better lift, but let’s ignore that for now) the sails SHOULD only push the boat downwind, but there’s a clever way to deal with that: a keel. The keel is a straight board in the water that’s parallel with the boat.

So let’s say wind is coming from the top of your phone, straight down. The sail is parallel with the boat/keel, moving 50 degrees to the left of going straight up, with 90 degrees being straight left. (Draw it out if it helps) There’s a component of force down yes, and that should push the boat back, but there’s a leftward component that is bigger than the down component. So the sailboat will go left more than down/back.

Now remember the keel, it’s in water which has much more friction than air. So the keel helps make the boat move in only two directions, forward or back. So whatever force is pushing on the sail pushed down to the keel, and is equalized out. The only part of the force that is allowed to push the boat forward is the remaining leftward force, which pushes the boat left, but that gets equalized out too by the keel, so the boat slips forward in the keel direction too.

In the end the boat is pushed left, but because of the keel, goes forward and left, along that 50 degree bearing.