Regarding sailing against the wind.
I’ve heard of this being done in stories about the sea and such, but I was never clear on the mechanics involved in doing this. Is there a site that explains (and shows) how this is done?
You don’t so much sail against the wind as you sail across it - with a slight amount of forwards motion. The process is called “tacking.” You go back and forth across the wind, and do it so as to make a little gain in the direction you wish to go with each direction change.
A slow process, and to be avoided if possible - so I gather.
I’m not a sailor (nor do I play one on TV.) Possibly sailor will show up before long with a good explanation.
Someone here (SDMB) made a model craft that used a windmill to drive a prop, this was direct drive with no ability to store energy (no batteries/generator/motor setup). IIRC it did ‘sail’ directly into the wind. I don’t know if sail would be a proper term for it due to the active motion of the prop. Also I did see some problems with the model but I assume it could work if scalled up anyway.
What Mort said. Depending on the boat and sail configuration, it may sometime be possible to sail as close as 20 degrees off the wind though most of us can’t do better than 30 degrees. Tacking eventually gets you where you want to go.
The sail(s) form an airfoil much like an airplane wing to provide forward power. You use the sail’s ropes (called sheets) to position a sail to get the best airfoil for the wind conditions and therefore the most power.
Sailing is a very expensive way to go someplace slowly, but we love it.
I know there are more experiences sailors on the board so perhaps someone will come along to provde a better answer.
When sailing anything other than directly away from the wind, you need to achieve a flow of air across the surface of the sail (rather than the wind blowing straight into the sail and pushing). The shape of the sail is then the crucial factor. A dead-flat sail will produce no forward motion, you need the curvature to produce an aerofoil shape. This then acts, as stated previously, in a similar way to an airplane wing, producing ‘lift’. In the case of a boat, the ‘lift’ is in the direction of the face of the sail closest to the wind, hence the motion ‘towards’ the direction of the wind.
As far as the aeronautical details of lift go, I shall have to leave that to others… I have tried to grasp it, but there sems to be considerable controversy over the Bernoulli principle, rate of flow on the high pressure side, etc etc. Suffice it to say, from my own perspective, it works! (If it stops working and I can only sail downwind tomorrow, I’ll let you know!)
Here is an interesting diagram, that will help discuss this topic.
Notice that the twelve o’clock position (and a region near it as well) is unsailable. Being close hauled, or beating to weather is the highest upwind that a sailor can ever expect to go.
This is a big topic Astro, and I regret I don’t have too much time to explain it, but as another poster said, the sail is an airfoil. The sails are not flat, but curved fore 'n aft. Wind that passes over the sail produces a low pressure zone that literally sucks the boat into its path.
That’s possibly unclear.
Here is some more information.
I was in the San Diego Naval Sailing Club when I was in jr. high, and I actually was an instructor for a few weeks. (Teaching the new members how to sail was part of advancing one’s training so as to be able to use larger boats.) But as usual, I’m too late to add anything useful to the answers already given.
In James Burke’s Connections, he mentions that sailing into the wind was impossible with square sails, and only with the invention of lateen rigging (triangular sails) did humans start to sail/tack in any wind direction. But he doesn’t explain why. I gather from reading this thread that it has something to do with the airfoil principle, but can anyone shed further light on this? Thanks.
Well there are entirely square-rigged vessels and they can tack against the wind too (probably less efficiently than fore-and-aft rigged vessels with the same sail area). Square sails form an airfoil shape by bellying out forward.
Connections is a good program, but Burke oversimplified if he said that. As explained above, you can sail against the wind by having the sail function as an airfoil instead of allowing it to push the sail. Both effects can be used with either square or triangular sails, and a variety of rigs, but fore-and-aft rigs are far better at the airfoil effect. European square riggers from the “age of sail” could manage about 60 degrees to the wind, whereas a modern recreational sailboat can manage 45 (actually, many can manage a bit closer, but 45 is very convenient - you tack through 90 degrees, and are headed at a right angle to the direction you were going).
From http://nabataea.net/sailing.html
His 56 1/4 is consistent with “about 60” in my book.
BTW, I was always taught that the fastest point of sail for a modern recreational sailboat is a beam reach - 90 degrees to the wind, where you get an optimal combination of push and use of the sail as an airfoil. For the square rigger, the fastest point is a broad reach - wind behind you at an angle.
As I think about it, that line doesn’t make physical sense, though it’s what I’ve been told by sailing instructors. Beam reach IS the fastest point of sail, but more likely because the triangular sail on a modern sloop operates as a very good airfoil at that point, imparting practically all of its lift forward.
Oh hell, cancel that that last statement. I should have let the original stand.
I wonder if anyone ever tried to come up with a wind-turbine powered boat? It would be interesting because, I imagine, sailing directly into the wind would be the easiest bearing of all. The obvious disadvantage would be evident when you wanted to go in the opposite direction, because as you move to leeward (there’s a salty expression,arrrrrgh) your relative windspeed would approach zero. But perhaps never actually reach it…any engineers around here who’d want to take a stab at this?
I guess Spectre of Pithecanthropus you didn’t read my post above:
Here’s a simple, “common sense” illustration that I believe accounts for some of the motion. This contradicts part of what Kymodoce said (about a flat sail), but I’m pretty sure it’s correct as far as it goes.
Imagine a toy railroad car on a straight track, with minimal rolling friction and minimal inertia. It has a flat sheet-metal sail angled at 45’ to the track. If you push, or the wind blows, on the sail at an angle of 90’ to the track, the pushing force will move the car along the track (we’re also going to assume that the car will not be pushed over onto its side). In pushing on the sail with your fingers, the fingers slip along the sail as the car starts to roll. The car can’t go sideways, the same direction as the push, because of the track – it can only roll forward (or backward) on the rails.
You can vary the angle of the sail to vary the proportion of forward motion of the car. If the sail is turned to parallel with the track, or turned to 90’ to the track, no forward motion (a vector of zero) is obtained. But with the sail anywhere between 0’ and 90’, some forward motion can be imparted to the car.
Likewise, going back to the sail at 45’, you can change the angle of the track relative to the pushing motion, and still get some forward motion of the car on the track. For example, you could angle the track 20’ toward the pushing force (wind or fingers) and still get the car to move forward. But now with the track angled a bit towards the wind, the car moves slightly towards the wind as it rolls on the track.
Having angled the track 20’ closer to the wind, you could adjust the sail 20’ so that it is 45’ to the wind, which I believe would give the optimum translation of the more-or-less sideways pushing force to forward-down-the-track motion.
The keel of a sailboat resists sideward motion, and to some extent has the effect of the boat being on a “track.” Obviously there will be some sideways slippage through the water, but the keel prevents the boat from simply going only in the direction of the wind’s pushing force. Angling the boat, and thus its keel, somewhat toward the wind is like angling the toy train track somewhat toward the wind. And the angle of the boat’s sail can be adjusted to the optimum for translating the sideways push of the wind into forward motion of the boat.
After that it gets more complicated. As mentioned, the pliability of the cloth sail and the shape it assumes become factors. The motion of the boat through the air produces an “apparent wind” with a different direction from the actual wind. And there is some sideways slippage of the boat. All of these factors, combined with the basic vector forces of the car/track analogy, come into play and have a bearing on what angle the boat can be turned toward the wind and what angle the sail needs relative to the boat for optimal propulsion.
But in essence, with a keel to direct which way the boat can move, and a sail whose angle can be adjusted for maximum effect, a wind approaching the boat at some sideways angle can produce some forward motion.
And then you get into ‘ice boats’, Bawahahahaha
Relative wind
Apparent wind
Wheeeeeeeeeee
According to this, you’re right.
You can say that again!
Apparent wind makes tacking into the wind faster than sailing downwind. When sailing into the breeze, the sail gets the effects of both the wind blowing and the boat moving through the air, and the sum of these move the boat forwards.
Indeed, the only way to sail faster than the wind is to sail into it.
Jaques Cousteau had a weird ship for a while that had a large pole that acted as mast and a sail at the same time. It was an experimental design. From what I remember the pole was shaped like a teardrop. I guess it wasn’t that great an idea since it didn’t catch on.