Eh... this is problematic stuff. Look to this threads:
http://www.subsim.com/radioroom/showthread.php?t=143775
http://www.subsim.com/radioroom/showthread.php?t=204399
When i was trying to play with this i never get good results. Even if it was looking good for first view, i found some problems later.
For example even if i changed values for boats only a bit and everything was looking good, when i attacked some convoy and boats start zig-zaging, the whole convoy was breaked, boats was blocking each other and AI was not able do any inteligent corrections.