AnniKa32 wrote:1. so, if i have the smooth algorythm, and if we make sure that a given industry will allways be in service with more than 60% then it will very unlikely close down?
In my experience it is.
AnniKa32 wrote:2. if a ressource industry production increased from 32coal to like 320coal because it had a good service for a while, and then for any reason, train crash or whatever, the rate is below 60%, will the industry then step down to the lowest value and close then, or is there a chance that it closes right in the first moment where its below 60%?
If you stop servicing an industry (for whatever reason), the rating drops, and from then, the chance to decrease production is slightly bigger than the chance for increase. Eventually, it will drop to 0 production, and close.
A temporary stop in servicing won't be a problem thus.
AnniKa32 wrote:just an experience how it was for us with 3 new players wich played first time:
we just started a server, and after like 10 minutes the messages spamms that the industrys are closing overall on the map
Previously, you said you played 2048x2048 or so. That is a very big map. A single player can play a game in about 512x512. A map of 2048x2048 is 16 times as much, you may want to start with something smaller at first. Also, you can use a lower industry density. The high ones are mostly for small maps, to force you get every industry type, but for large maps, it just dumps a few thousand industries over the map, causing lots of "closing down" messages, as you won't be able to give good service to almost all industries.
Last but not least, start with shorter routes so you get to the servicing point quicker.
AnniKa32 wrote:this is pretty annoying since we dont even have a chance then to pick a good route on the map to build. we was 5 players, and 3 of us (2 new players) was still constructing the train tracks where the industry wich they wanted to build to just dissapeared.
Sure it was 10 minutes? Default industries are protected for the first 5 years, which amounts to 5*13 minutes ~= 1.5 hours real time. Maybe you had it set to fast-forward (left-most button with the >>)? In that case, yeah, 10 minutes is feasible

Alternatively, maybe you made a map, spending more than an hour on that map (~4 game years), you loaded that map on the server and started playing? Then the 5 year protection also ends in a year, as the major part of protection time was 'used' while making a map.
When playing MP in coop, we usually stop time (the server owner), and plan and discuss what to do. Once a cunning plan has been made, we start time again, and start building.
AnniKa32 wrote:i think this is really annoying, there should be an option to secure an industry, as example with a montly fee or pay something and the industry wont close for 1 year or something, or if you place a station nearby an industry it should have a quaranted time to not close for like a year or something like that, so players that are not so fast in constructing and plannig the track also have a chance to finish before the industry dissapears.
The default industries are from the TTD era. Due to backwards compatibility, that cannot be changed. You do have the 5 year protection though. If you want something else, there are industry NewGRFs. The list is a bit too long to discuss now. (A wiki page would be nice with a list of them, don't know if it exists.)
AnniKa32 wrote:for the new players this was really annoying and they felt like not playing this game anymore, so that we decided to use manual industries with closing off.
Yep, much of default game is less than optimal to play to say the least, but we're stuck with it due to backwards compatibility. However, there are lots of NewGRFs to tweak the game in the direction you like, which is what most players do.