Guiding Ships with Moire Patterns (2018)
Navigating Waters via Moire Patterns (2018)
Originally posted on March 28, 2018, by mechatronicsguy on the "Tinkerings" blog—a digital sanctuary for personal musings and technical experiments.
⚓ The Inspiration
My curiosity was piqued by a fantastic video from Tom Scott, who explored a specialized lighting system known as "Inogon" lights. These are designed to help maritime vessels navigate through harbors or narrow channels.
To dive deeper into the mechanics, I consulted the following resources:
- The Patent: US4629325
- Military Analysis: A DTIC report regarding its efficacy.
Spoiler alert: The military wasn't particularly impressed with the system.
🛠️ The Build Process
Using Inkscape for the design and a laser cutter for fabrication, I attempted to recreate the system by adhering closely to the patent's specifications.
Implementation Checklist
- Design masks in Inkscape
- Calculate pitch-to-width ratio
- Laser cut the grids
- Assemble and back-light
The Technical Specifications
The patent suggests a ratio of pitch spacing to dark band width between and . I opted for a value of .
Mathematically, this can be expressed as:
This specific configuration results in a duty cycle of approximately . Additionally, I ensured the first mask contained exactly one more band than the second mask.
👁️ Visual Observations
When the device is illuminated from behind and viewed head-on, the effect is striking.
Note: You might notice some slight circular distortions. This is simply because the distance between the two grids is significant relative to my viewing distance. If this were installed on a shoreline and viewed from away, those effects would vanish.
⚖️ Critical Analysis: Moire vs. Traditional Guidance
Is this the ideal way to guide a ship? While it is a nifty, intuitive design that requires minimal calibration and supports multiple simultaneous users, it has a fundamental flaw.
Harbors require a razor-thin, platonically perfect path. In reality, harbors have a general safe zone that a captain should stay within. The Moire system provides constant steering corrections even when the ship is in a perfectly safe area, just slightly off the center line.
Comparison Table
| Feature | Moire System | 3-Lamp System |
|---|---|---|
| Guidance Type | Precise Line | Safe Corridor |
| Feedback | Constant adjustment | Threshold-based |
| Stress Level | High (requires perfection) | Low (indicates danger) |
| Best Use Case | Narrow targets (e.g., cables) | General Navigation |
The "Three-Lamp" Alternative
Years ago in Newcastle, I encountered a more elegant solution using three lights.
The logic follows a simple spatial alignment:
🏁 Final Thoughts
Navigating a massive ship involves juggling cross-currents, weather, and other traffic. Forcing a pilot to adhere to a singular, invisible line increases fuel consumption, mental fatigue, and the risk of collisions as every ship crowds the same path.
I would personally prefer a system that tells me when I am actually in danger, rather than one that tells me I've deviated from a theoretical line on a map.
That said, the Moire system is a brilliant application of mathematics. It is incredibly useful for marking very narrow objects—such as the submarine cables mentioned in the Tom Scott video—to prevent anchors from snagging them.
📂 Resources
If you want to build your own, the files are available here:
https://www.thingiverse.com/thing:2842603
