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| Sail Physics |
 Title text: Turning in other directions can be accomplished by using a magnetized centerboard and ocean currents, since a current flowing through a magnetic field induces a Laplace force. |
Explanation
This comic starts off looking like a typical explanation of how sailboats can travel upwind — a topic that continues to spark debate and refinement in physics circles. However, it quickly veers into a completely fictional and incorrect theory involving triboelectric charging and the Lorentz force, rather than referencing real mechanisms like aerodynamic lift.
This humor works at another level — most interaction of physical things at macro scale (humans and boat sized objects) are electromagnetic in nature. So one unaware of sailing mechanics may start to explain the situation with electromagnetism, and could come to this line of thinking, but it is wrong. If we are to consider this, we find that either no force is appearing in the direction shown, or very little.
The first panel is a fairly accurate diagram used to explain the reasons why a boat can sail into the wind (see below), it just sets up the scenario.
The second panel portrays the triboelectric effect, which is transfer of static charge through the motion between two 'objects', which in turn depends on effective interaction surface area. It shows charge being accumulated by the wind stripping electrons from the sail of the boat, leaving the sail positively charged. Among other problems, the charge that can be acquired is typically very small.
The third panel shows the boat being blown sideways by the wind, which a sideways-facing boat hull would highly resist (see below). This motion of a charged body through the Earth's magnetic field, however, results in a Lorentz force. Depending upon the relative directions of motion and the magnetic field, this could generate a perpendicular force in the direction the hull is pointing, as indicated, assuming the entire premise was even as promised.
The final panel demonstrates this force diverting the downwind (and sideways) motion of the boat forward. As well as the various other problems that exist with the whole scenario, this is contrary to promise of allowing the boat to sail upwind, as the originally indicated wind direction and the finally indicated path results, if anything, in movement slightly downwind.
The title text invokes further technobabble to suggests using a magnetised retractable keel to adjust the nature of the forces. It conflates ocean currents (the global flow of water) and electric currents (the movement of charged particles). Perhaps from the supposed ability to move the magnet through the charge, as opposed to the other way round. It invokes the "Laplace force", which is just a technical variation of the Lorentzian one.
The More Correct Explanation
Your speed of sailing perpendicular to the wind tends to be greater than that which you can achieve heading at any angle into the wind, but this is no use if you wish to sail to a destination directly in the direction the wind is coming from. Aiming at an angle into the wind and tacking (briefly use your existing speed to turn directly across the wind), lets you combine sets of aiming off to slightly one side of the wind and doing the same slightly to the other, as required to reach your destination. The expert sailor can choose the point of sail to the wind that makes for the fastest journey time, combining the possible speed and the necessary amount of additional distance. Similarly, turns ('jibes') across the wind allow a more optimal passage to a directly downwind destination than running straight with it.
Supposing that the comic physics had been more capable of doing what it suggests, tacking/gibing could also be important concepts. With two sails made of different materials, one could unfurl that which is able to accumulate a positive charge (by losing electrons) or else another that accumulates a negative charge (by 'borrowing' electrons from the air). In this way, you could account for how the effective direction (and declination) of the magnetic field would be different for any given location, wind direction and intended destination and perhaps eventually make progress in whichever direction the vessel is required to go.
Transcript
- [Four panels show a schematic sail boat, seen from above, to indicate how it can sail into the wind. In the first panel the boat is heading straight up in the panel. The sail is fixed at the bow and describes a slight curve going to the right of the boat and then curving to the left, ending close to the stern. The rudder can be seen behind the boat. Five arrows, pointing towards 4:30 on a clock face, are drawn at the top left part of the boat, indicating the direction of the wind. There is a frame above the drawing of the boat with text. And then the arrows are labeled, and small lines going to the sail and the hull of the boat connects with two more labels:]
- How sailboats use physics to sail upwind:
- Wind
- Boat
- Sail
- [In the second panel the boat is drawn similar to panel 1, but the wind arrow have been changed to showing how the wind now blows past the sail on either side. This is done with two lines of three arrows that goes on either side of the sail, and the second and third arrow bends to follow the curve of the sail. Charged ions are shown across both sides of the sail with positive on the left side of the sail, (over the hull of the boat) and negative on the right side, over the sea to the right and behind the boat. The positive charges are small + signs in circles and the negative minus signs in circles. Above the drawing there is the following text:]
- 1. Wind passing over the sail strips away electrons via the triboelectric effect.
- [In the third panel the boat has turned towards right and has been moved closer to the bottom of the panel (this could be to acomodate more text above though). The entire hull is now covered in positive charges. A large broad dashed vector is shown going in the direction of the wind. The arrow is not over the boat but on either side of it, with the arrow head ending right of the stern of the boat. Two thin arrows are shown above the end of the force vector. A short solid arrow, that points along the same direction as the large arrow. And then a dashed arrow is drawn perpendicular to the first of these thin arrows (pointing along 1:30 on a clock face. Above the drawing there is the following text:]
- 2. The positively charged boat is blown downwind; its movement in Earth's magnetic field produces a Lorentz force.
- [In the fourth panel the boat has turned even more towards right and is back to the same height in the panel as the first two panels. The entire hull is still covered in positive charges. The broad dashed vector is still shown, but after starting in the wind direction it can be seen to turn slightly upwards before reaching the boat. And then when it comes out the other side of the boat it points in the direction of the bow of the boat, the arrow ending in front and a bit to the right of the boat. The two thin arrows from before are now shown to the left of the boat , with the short solid arrow pointing along the same direction as the start of the large arrow. And then a the dashed arrow drawn perpendicular to the first of these thin arrows pointing in the direction the boat is sailing. Above the drawing there is the following text:]
- 3. The Lorentz force acts perpendicular to the direction of motion, redirecting the boat upwind.
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