Most of the time, we mark docking lights as headlights. But they are not headlights and are not meant to be used to illuminate anything other than a dock. Docking lights are not for navigation. They do a great job of illuminating docks when it’s dark out and you are trying to pull into a sled.
When driving at night, you need headlights to stand a chance of seeing anything. If you look at a ship at night, they don’t have headlights! Ships turn off as many lights as possible to make themselves as dark as possible. But why don’t boats have headlights? If headlights work for cars, why not for ships? It’s because the headlights are useless for boats. Let’s learn more about it.
Why don’t boats have headlights? (Scientific Explanation)
A headlight is a light source that emits photons that can bounce off objects and return to your eyes. Your brain then interprets them and tells you what you’re seeing. But you need a light powerful enough to illuminate the area you’re looking at. The light’s power is dispersed across its beam’s full width. Then when the light hits an object, the small bit of its beam that hits the object is reflected.
It is again dispersed, meaning that only a tiny fraction of the original light returns to you. That’s fine in a car. You want a narrow-ish area right ahead of you, extending out far enough that you can take action to avoid the things you see. Even at motorway speeds, around 100 meters should be enough.
- With a boat, 100 meters is not enough to take any action.
A large cargo ship needs more than a mile to stop with two such vessels approaching each other. We need at least two miles of visibility to take action in time. Do you know how bright a car’s headlight is? Think how much brighter a ship’s headlight would need to have the same effect.
- Ships still use lights, but they’re nav lights.
Every seaworthy vessel is fitted with nav lights. The idea is that they’re arranged in a standardized, distinctive way so that other vessels can see you. Also, it is for identifying how you are moving as nav lights are fitted to the target vessel. Their power only needs to be sufficient to be seen by other vessels.
If you have a light fitted rather than relying on a tiny portion of reflected light, you can see how much easier it will be to see than using a headlight. But what about identifying their movement? Let’s take this cargo ship as an example. She would show two-mast headlights, the aft being higher than the forward one. These immediately tell other ships which direction she’s moving in this configuration.
- These are the colored lights you know about: red for port and green for starboard.
Again, it reinforces which way she is traveling. But the lights can tell us even more than that. If we look at the vessel’s port side and she turns towards us, watch what happens to the lights. You can start to see both sidelights. The other vessel is heading straight for you.
From above, you can see that the only angle where you would see all those lights is right ahead. The observant among you will spot that these lights don’t go all the way around either. Instead, we have a single white light filling this sector at the stern.
If you spot a single white light, one of the things it could be is a power-driven vessel viewed from astern. If she turns a bit, you might come on the cusp of viewing her sidelights and mast headlights to looking from above.
Nav lights tell you so much more than headlights ever could. They accomplish the basics, making the vessel sharp against the dark sky. But in addition, they allow you to identify the vessel, type, work out its aspect and see which way she’s moving.
9th and 10th Vic. c. 100: “An act for regulating steam navigation and requiring sea-going vessels to carry boats.
“Steamers’ lights – to prevent a collision.” The London Gazette.