U-boat visual detection range
 

It's now become clear that our previous (and formerly correct) understanding that time of day had no impact on visibility was stealthily shattered sometime around update 0.20.

After some empirical research, below are the visual detection ranges as of game version 0.20b (current).

Note that night time represents the extreme (no moon, pitch black) and so does day time (the brightest it can get), while dusk/dawn is calibrated to about the average amount of light around that time of day. Anecdotally, the exact amount of light influences the equation somewhat, so take the figures below as a rough guideline rather than gospel.

https://i.imgur.com/1dOYtTH.png

Yes, this means that you can now do Kretschmer-style night attacks :)

Kudos to Koji and Lucifer for hopping on my boat while I was running the experiments, and not dying of boredom :P

Detection Ranges
 

Thank you sir. Saved a lot of guys a lot of tedium there.
At full moon I've ran alongside a Flower at 800 meters out while matching his course and speed. Never detected.

(15 OCT 40, Biscay, approximately 2100hrs, medium setting)

We ran about 800 m away from a Sloop and was never spotted, even though we could clearly see the Merchant ships in the distance (about 4000 m).

1941, night time with low Moon (ship outlines easily visible due to looking "up Moon" (Moon was behind us).

A Warm Welcome To The Subsim Community > VonHoffman
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What do people think about these effectively digital ranges?

Ideally whether or not one is observed should be a very low base chance per minute, increasing or decreasing with:

Lighting
Being silhouetted
Surfacing or Diving
Aspect (side on or pointed at the viewer)
Height
Gun-flashes
Weather
Observer being alerted to a U-boats position

...and so forth.

In other words if you can see the convoy, then you're not utterly safe from observation at any range, or any light-level etc. Instead in disadvantageous conditions for the AI observer eg night, fog you can be pretty sure of being unobserved, but not completely certain...

I don't know how the model works now, but I would like the game to "simulate" the vision of people on the ships. Like, the game simulates one person on the bridge looking in the forward direction of the ship. That results in an oval shape in front of the ship, on the water, where he is looking right now. Like a beam (obviously not rendered in-game). That beam would move around the ship as he is looking in different directions. If your submarine is inside of the oval beam shape, you are detected (or at least there is a risk of detection). The closer to the ship he is currently looking, the bigger the beam is. And the further away, the smaller it is. This means that the risk of detection from afar is very low, because this beam would be very small and very unlikely to "hit" your sub. But if it does, he could see you!

Multiple ships will all have these beams wandering around, making it risky to approach a convoy because of so many eyes. Also, if you've been detected, a lot more people on the ships will be on alert and many many more beams will look for you!

The risk for detection when you're inside the beam could depend on things like sun position, moon position, sea state, speed etc. Even if he looks directly on your periscope a rough night, there is a chance he misses it.

The purpose of this, besides achieving some realism effects, is to add a lot of randomness to it.