Vision rolls to see landmarks at sea

[Anthony]

Originally Posted by Michael Thayne

Maybe the real range of possibilities is greater than that? I don't know.

Haze penalties should basically be "-1 per X distance"; real-world standards for visibility are a factor of 20 reduction in contrast, which is probably around -8.

[Michael Thayne]

Originally Posted by Anthony

Haze penalties should basically be "-1 per X distance"; real-world standards for visibility are a factor of 20 reduction in contrast, which is probably around -8.

Yeah—but what's a reasonable value of X for a clear day at sea?

[Anthony]

Originally Posted by Michael Thayne

Yeah—but what's a reasonable value of X for a clear day at sea?

Seems to depend on humidity; could be as much as ten miles in mountain air, but over water I doubt it's going to exceed 2 miles over water. You'd want to look into real-world visibility standards, and divide listed visibility by 8 or 10.

[Dalin]

I'm not an expert, but this site seems useful for atmospheric purposes:

https://www.sciencedirect.com/topics...on-coefficient

I've always found this sort of thing interesting. One of the very first dynamic web pages I ever created (in the early 1990s) was a calculator that would determine potential visibility given the height of the observer, the object being observed, and the size of the planet. This was cool, but I never figured out how to introduce atmospheric haze into it, so it didn't reflect reality very well.

[Michael Thayne]

Originally Posted by Anthony

Seems to depend on humidity; could be as much as ten miles in mountain air, but over water I doubt it's going to exceed 2 miles over water. You'd want to look into real-world visibility standards, and divide listed visibility by 8 or 10.

Apparently it is sometimes possible to see the Chicago skyline at 50+ miles over lake Michigan. So 5-7 miles might be the real maximum under absolutely ideal conditions. But maybe 2 miles fits more typical conditions.

[johndallman]

Originally Posted by Anthony

Seems to depend on humidity ...

And temperature. Slight mists that city-dwellers never notice provide significant concealment at sea.

[RGTraynor]

Mm ... all that being said, people are focusing on Vision to the exclusion of experience. It's well known that skilled navigators could spot islands and landmasses from distances beyond normal sight, just by how clouds and the light of the sky were set.

Wind is also a factor: the stronger the wind blowing towards you, the harder it is to see things at sea ... never mind if it's gusty enough for spindrifts.

[Michael Thayne]

Originally Posted by RGTraynor

Mm ... all that being said, people are focusing on Vision to the exclusion of experience. It's well known that skilled navigators could spot islands and landmasses from distances beyond normal sight, just by how clouds and the light of the sky were set.

Wind is also a factor: the stronger the wind blowing towards you, the harder it is to see things at sea ... never mind if it's gusty enough for spindrifts.

Suspect this aspect of the thing might be best handled by allowing Per-based Navigation or Area Knowledge rules, rather than mucking about with modifiers.

[Rupert]

Originally Posted by Michael Thayne

Apparently it is sometimes possible to see the Chicago skyline at 50+ miles over lake Michigan. So 5-7 miles might be the real maximum under absolutely ideal conditions. But maybe 2 miles fits more typical conditions.

On a very clear day you can see Mount Taranaki/Mount Egmont from my parents' house, 115 miles away. On a slightly less clear day you can see Mount Ruapehu, 80 miles away. However, as these are mountain peaks, much of the line of sight is in higher, dryer and cleaner air.

Where I live, in a coastal city, I've yet to see official visibility given as better than 10km, and it's listed as "10km. Light Haze is affecting visibility." This seems to be code for "about as good as it gets, but not perfect". This implies -1 per kilometre.

So tif we can answer "How much more or less hazy is the Eastern Mediterranean than the South-West Pacific?" we can tell what a typical penalty for there is.

[Anthony]

Extreme visibility where I am is being able to see the Farallon Islands, which are around 40 miles away. That's over water and mid-latitude so decent equivalency.