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xkcd #3013: Kedging Cannon (xkcd.com)

submitted 4 days ago by [email protected] to c/xkcd

30 comments fedilink hide all child comments

The real key was inventing the windmill-powered winch.

https://explainxkcd.com/3013/

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[–] HappycamperNZ 9 points 4 days ago (1 children)

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.

[–] [email protected] 5 points 4 days ago (3 children)

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!

[–] [email protected] 7 points 4 days ago

You're one of today's lucky 10,000.

[–] HappycamperNZ 4 points 3 days ago

All good, its much more than that but gives a general idea

[–] waz 1 points 4 days ago (2 children)

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.

[–] HappycamperNZ 2 points 1 day ago

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.

[–] [email protected] 2 points 3 days ago* (last edited 3 days ago)

That's too complicated. I'm just going to keep using the kedging cannon.