3119: Flettner Rotor

2025-07-24T12:56:26Z

Mandelbrot:

{{comic
| number = 3119
| date = July 23, 2025
| title = Flettner Rotor
| image = flettner_rotor_2x.png
| imagesize = 385x359px
| noexpand = true
| titletext = "And in maritime news, the Coast Guard is on the scene today after an apparent collision between two lighthouses."
}}

==Explanation==
{{incomplete|This page was created by a spinning shaft. Don't remove this notice too soon.}}

Randall is pointing out that a {{w|Flettner rotor}} can make a boat look like a lighthouse, and thus make the other boats give the right of way, in reference of a [https://en.wikipedia.org/wiki/Lighthouse_and_naval_vessel_urban_legend famous urban legend] about a fictional conversation between a ship and a lighthouse both asking the other one to change course to avoid collision.

A vertical-axis Flettner rotor is a smooth cylinder which is spun along its axis. As air passes across it from the side, an aerodynamic force is generated at a right-angle (i.e. forwards) to propel the boat in the desired direction. If a directional light were attached at the top, it too would spin, sending out periodic flashes of light just like a lighthouse. Or, as it appears to be in the comic, a fully working {{w|Lighthouse#Components|lantern house}} may be fixed to the top of the non-rotating core to the rotor, within which its light rotates at a more usual rate independent of that of the vertical rotor.

A vessel directly in the path of the moving boat would have to perhaps consider the possibility that they are drifting towards rocks, but how one ''at anchor'' (and not obviously dragging its moorings) could reconcile the conceptual movement, especially if GPS data gives no reason to believe it, is left unexplained.

Alternatively, a single Flettnerized boat complacently collided with an actual lighthouse, having similarly dismissed it as another boat that should have been avoiding itself. Thus, tangentially alluding to the old {{w|Lighthouse and naval vessel urban legend|urban legend}} in which a naval vessel insists that another radio operator at sea diverts course to avoid a collision, demanding right of way by citing their military importance, only to be embarrassed when the other operator reveals they are not another sea vessel, but a lighthouse.

The title text describes "an apparent collision between two lighthouses", which could refer to two Flettnerized boats colliding with each other because they were ''both'' assuming that everyone else will give them the right of way.

==Transcript==
:[A panel showing Cueball standing on a Flettner Rotor Sailboat, which is decorated with rocks and a lighthouse-top on the Flettner Rotor.]
:[Text beneath panel:]
:Sailing tip: If you have a Flettner Rotor Sailboat, you can add some fake plastic rocks and a light to make other boats give you the right of way.

{{comic discussion}}<noinclude>

3119: Flettner Rotor

2025-07-24T12:55:18Z

Mandelbrot:

{{comic
| number = 3119
| date = July 23, 2025
| title = Flettner Rotor
| image = flettner_rotor_2x.png
| imagesize = 385x359px
| noexpand = true
| titletext = "And in maritime news, the Coast Guard is on the scene today after an apparent collision between two lighthouses."
}}

==Explanation==
{{incomplete|This page was created by a spinning shaft. Don't remove this notice too soon.}}

Randall is pointing out that a {{w|Flettner rotor}} can make a boat look like a lighthouse, and thus make the other boats give the right of way, in reference of an urban legend{{citation needed}} concerning a fictional conversation between a ship and a lighthouse both asking the other one to change course to avoid collision.

A vertical-axis Flettner rotor is a smooth cylinder which is spun along its axis. As air passes across it from the side, an aerodynamic force is generated at a right-angle (i.e. forwards) to propel the boat in the desired direction. If a directional light were attached at the top, it too would spin, sending out periodic flashes of light just like a lighthouse. Or, as it appears to be in the comic, a fully working {{w|Lighthouse#Components|lantern house}} may be fixed to the top of the non-rotating core to the rotor, within which its light rotates at a more usual rate independent of that of the vertical rotor.

A vessel directly in the path of the moving boat would have to perhaps consider the possibility that they are drifting towards rocks, but how one ''at anchor'' (and not obviously dragging its moorings) could reconcile the conceptual movement, especially if GPS data gives no reason to believe it, is left unexplained.

Alternatively, a single Flettnerized boat complacently collided with an actual lighthouse, having similarly dismissed it as another boat that should have been avoiding itself. Thus, tangentially alluding to the old {{w|Lighthouse and naval vessel urban legend|urban legend}} in which a naval vessel insists that another radio operator at sea diverts course to avoid a collision, demanding right of way by citing their military importance, only to be embarrassed when the other operator reveals they are not another sea vessel, but a lighthouse.

The title text describes "an apparent collision between two lighthouses", which could refer to two Flettnerized boats colliding with each other because they were ''both'' assuming that everyone else will give them the right of way.

==Transcript==
:[A panel showing Cueball standing on a Flettner Rotor Sailboat, which is decorated with rocks and a lighthouse-top on the Flettner Rotor.]
:[Text beneath panel:]
:Sailing tip: If you have a Flettner Rotor Sailboat, you can add some fake plastic rocks and a light to make other boats give you the right of way.

{{comic discussion}}<noinclude>

explain xkcd - User contributions [en]

3119: Flettner Rotor

3119: Flettner Rotor