Question: Is ability of boat to maintain depth tied to crew ability?
 

I noticed that when I order a depth like 120 meters it becomes very hard to maintain depth or even to ascend again without blowing balast. Is this realistic? Is it somehow tied to the crew's abilities?

No one is quite sure if it's tied to crew experience or due to the sub buoyancy modeling.

Further reading
http://www.subsim.com/radioroom/showthread.php?t=165011
http://www.subsim.com/radioroom/show...ighlight=awful

Plus
http://www.subsim.com/radioroom/showthread.php?t=165478
Mod that changes sub buoyancy.

Thanks Sergei, that explains alot. :)