The short answer is there is no set number of distance for vessels operating in "restricted visibility" , rather there is a set of guidelines set forth in the International and Inland Rules of the Road governing your speed, look outs and conduct when operating in the fog. Rule 19 will specifically address this question in detail. Please check out the link provided below for more detailed info. Check out Rules 2,4,5,6,7,8, 19 & 35.
Vessels must show the running lights suitable for their class or the operations in which they are engaged between sunset and sunrise and during restricted visibility. There are no special or extra lights required for fog.
A fog light uses a different light beam to reduce how we see when there is fog. Regular high beams make fog appear more dense, or thicker. Low beams reduce that effect, but limits sight distance. Fog lights gives more sight distance without making the fog look more opaque.
Fog does not really exist as a feature of Minecraft, it is designed to help Minecraft run faster if you have the render distance turned down. To toggle fog and how thick the fog is go into the pause menu click options then video options. From here you can set the render distance, far has no fog while tiny has very thick fog. Please note that turning up your render distance may cause Minecraft to run slowly.
fog -> at land level cloud -> in sky
There isn't really a distance when you should use your fog lights, Switch on headlights, dip them if necessary and turn on fog lights if visibility is reduced. Fog lamps are very bright, however, so if you can see the vehicles behind you then it's likely they can also see you. In this case your fog lights will dazzle other drivers so turn them off
Adjust your speed so that you are able to stop on the amount of road that is visible. Use rear fog lights if visibility is less than 100m. Front fog lights are sometimes beneficial and high beams will dazzle you and decrease visibility.
I believe the navigation lighting requirement is that they have to be displayed between sunset and sunrise, and during periods of limited visibility such as fog, rain, or haze.
Switch on headlights and fog lights if you have them, drive no faster than a speed that you can safely stop in the distance you can see to be clear.
Press 'F' to change your fog render distance.
Fog lights are low lights on the car that provide greater road visibility in poor lighting conditions such as fog, rain or snow. They are not generally frequently used and are not statutorily required in some countries.
Fog, mist, dark
Fog is created by the tempurature and weather and a cloud is created by evapourated water