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xkcd #3013: Kedging Cannon
(xkcd.com)
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this post was submitted on 19 Nov 2024
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Edit: I have been corrected. Please read the follow-up comments for better information. I'm leaving the original text below for context and transparency.
As I understand (I'll happily be corrected), the basic mechanism is that you want to align your ship diagonally off to the side, and the sails at a shallow angle so that the wind pushes you to the side (diagonally back and to the side, but the hydrodynamics of your bow resist the backwards component), so you gain some momentum. Then you turn into the wind to have that momentum carry you forward, sails parallel to the wind so it doesn't push you back as much. Turn off to the side again (either back to the same side, or continue your turn to the other side) and repeat.
It doesn't move you quickly, because it's rather inefficient in transferring the wind's power into opposite momentum, but it gets you moving at least a little.
Not sure if you're wrong or im misunderstanding what you are saying.
When sailing upwind think of sails as an aircraft wing with the top facing forward. As the wind passes over them from one side they generate "lift" at a perpendicular angle to the sail, pulling the boat in that direction, usually a combination of forward and sideways. The sideways is offset by your underwater profile, that resists sideways movement, resulting in (mostly) just the forward movement.
Square rigs like this comic often struggle sailing upwind compared to sloop rigs with two sails as the fore sail is used to generate that lift on the mail sail.
I've oversimplified this a lot so please not nit pick too much.
Sounds like I had it mostly wrong. I definitely didn't know about the wing / "lift" / pull mechanic. The only part I did get right was that the sideways component of the force is offset by your ship shape, and even that I misphrased.
Thanks for the correction!
You're one of today's lucky 10,000.
All good, its much more than that but gives a general idea
A fun next lesson is the benefit of apparent wind. In addition to the wind relative to the water, you have added wind generated by the movement of the boat. Since the lift generated is related to the speed of the wind relative to the boat, the faster the boat goes, the more lift you get. As a result, it is possible to actually sail faster than the wind speed of the wind relative to the water.
I'm pretty sure I did a bad job explaining that. Google can explain it better for sure.
Similar thing - aparent wind shifts the wind direction forward. As such, how close a boat can sail to the wind decreases as the boat speeds up.
Not of the bow, but the center of all lateral resistance, which must be aft of the center of effort (sails). This includes the hull and rudder, but more important is the daggerboard/centerboard/keel, otherwise you would just be pushed downwind.
Keel was the word I was thinking of, but couldn't remember. Thanks for the correction!
And so Kedging is used only in tighter spaces where angles are not an option, like harbors or rivers
Also, while it doesn’t move you quickly, it still feels super fast due to the headwind adding to the feeling.