DustinLC

OK, I know it uses the wind and you angle the sail in such a way that move your boat/ship forward. That's all I know.

I've always wonder how ships go around before the motor ship existed. I'm sure they look for existing wind/current route but how do you get to point B from A and get back to A with a sail? Surely they don't wait until the wind actually blows the other way or take an extra 1000mi to get back to A? Or do they? Perhaps that's why the Argonaut has so many rowers ?

CharlesD

You can sail "into" the wind or basically be blown along by it in the general direction of the wind. Of course no boat can sail directly into the wind, but some can sail upwind better than others. The old square rig ships weren't very good going into the wind, so for a given wind direction there was a large range of directions that a ship could not move in. So, yes, basically they either had to wait for the wind to shift or go far out of their way to get to their destination.

DavidMich

It's called "tacking".
You (basically) zig-zag into the wind by angling the sail.

The choices we make define our lives, because choice, not chance, determines destiny.

Andrew W

In fact, you can sail without tacking most of the time.
If you are with the wind directly behind you, you are running. But if the wind is 90 degrees to your direction, you are reaching and you can make very good speed this way. Tacking is the only time you have to go back and forth across your intended path. So the wind from 3 main quadrants is good and the wind is only bad from one quadrant.

Andrew in Austin

wally

I believe when you tack, sail into the wind, you are basically using the sail as an airfoil.

The air travels faster over the leading side creating lower air pressure (lift on a aircraft wing) so the boat is “pulled” forward into the lower pressure air, or pushed forward by the higher pressure on the aft side of the sail.

However it works, it sure is fun!

DustinLC

Sound to me like you need a degree to go sailing .

I live in the San Francisco Bay Area and I watch guys that do board sailing. I'm not sure that is what you call it. It's a surf board with a sail on it and the rider climb onto the board and set up the sail .... and off he goes out and comes back in. The whole time, the wind is blowing in my face from the marina bay so I'm wondering how he can get out in the first place. I understand how he can get back in but getting out is against the wind.

I guess you guys probably explained it already but I haven't had time to draw out what the hell you guys are talking about .

DustinLC

OK. If I was going down a hill on my bike, I can go straight down or zig-zag to go down left or down right but how do I zig-zag up/back?



That hurts my brain .



Using my bike down the hill analogy, how do I go up/left or right while the hill is forcing me down? If I have a sail on my bike, I can image going down left, down or down right.

CharlesD

Tacking would be like a hill that you can't go straight down on your bike, but you can go at angle... so you go at an angle to the left, then turn to the right. The boat isn't being blown along by the wind, but is using the wind flowing over the sails like an areofoil. This is when you see boats heeled over at an angle. The wind is coming from ahead and to one side or the other of the boat, not from behind.

When a boat is tacking it is trying to move upwind, so it sails as close to the wind as possible. Say the wind is from the North and that is the direction you want to sail in. And say our boat can sail no closer to the wind than 45 degrees, so you sail toward the North East, then after sailing for a while in this direction, you tack so the bow of the boat swings around and points into the wind and then past that point so that the wind fills the sails again from the other side of the boat and you are now pointing 45 degrees away from the wind in the other direction (the momentum of the boat lets you do this.) Now you are sailing to the NW. Repeat as needed.

Keith Mickunas

Dustin, there's a few things going on. First, by doing the zig zag, you aren't going straight into the wind, which makes it easier to do. To equate it to a bike is a not very good, but look at it this way, what's easier, going straight up the hill, or at an angle?

I don't understand it all, but I'll take a shot at explaining it.
Have you ever seen the diagrams explaining how an airplane wing works? A sail is very similar but on the side. The sail forms a wing like shape as the wind blows on it, and then it causes the high-pressure/low-pressure imbalance, which causes the sail to move forward in the air. The direction that this pull has is mostly controlled by the orientation of the hull in the water.

imported_BrianW

Actually, the bike analogy can work, as long as you have an external force, like a pickup truck with a rope tied to the hitch.

What everyone has said about the sail behaving like an airplane wing is correct. When tacking at maximum angle into the wind, the force produced by the wind on the sail will push the sail toward the convex (low pressure) side of the sail. So if you have your sail nearly in line with the wind, this force will be almost perpendicular to the wind. (It'll never be completely perpendicular, because you have to tilt your sail a little to maintain the airfoil shape. Because of this, there will always be a component of force that pushes you in the same direction as the wind is blowing.) This sideways force is enough to get you going sideways in the wind. The way you convert this to motion into the wind is by simply pointing the boat upwind. The sail will pull the boat sideways in the wind, but it will go upwind at an angle, because that's the direction you point your boat.

Likewise, if you are on a hill on your bike, and you're holding on to a rope being dragged by a pickup truck moving sideways across the hill, you can steer your bike to go up hill, even though the force is sideways, and not up the hill. The more you align your bike straight up the hill, though, the less helpful the pickup truck will be. If you try to go straight up, the pickup truck will just pull you over, and you won't make any progress up the hill at all. The same tradeoff between speed and direction is true for the sailboat.