Visual detection
 

I´m using GWX.

1. What are the approx. ranges for visual detection by AI?

2. At different weather conditions?

3. Warships vs. cargo. Same AI detection range?

You've asked a big set of questions with a range of parameters. Generally if you check out the contents of sensors.dat you can find the answers.

Have a look at this thread which deals mostly with radar and sonar sensors but is pertinent to visual as well. http://www.subsim.com/radioroom/showthread.php?t=103709

Running decks awash I've been able to pass to within 1000m of a DD in 1940 in bad weather, but have also had my scope seen at 1800m in calm weather in the same year. A lot depends on the quality of the crew also. Elite DD's later in the war will pick you up on radar much earlier than they will see you anyway.

Visual detection depends on weather conditions. On a clear day you can see a ship up to 20Km away, and they can see you from a distance of about 6-8Km. At night obviously these distances deminish. On bad weather conditions the distances become even smaller, but it reality what matters is the relative experience of the look out crews. I don't think there is a difference in the spotting range between merchants and warships.