Hi hjl,
I agree that poorly done AI can interfere with the pleasure that one can take in careful navigation. Some otherwise good missions are turned into a crapshoot by forcing the player vessel to cross a line of AI.
Given the technical problems in getting AI to obey COLREGS, creators should be very careful about placement of AI paths. Players, on the other hand, should also understand the limitations and behavior of AI, and operate under Rule 2 whenever they are near an AI vessel.
In SS08, AI ships move along defined paths. If, for some reason, they are forced off of their path, they go into headless chicken mode. They cannot change course to avoid collision. They will attempt to stop in a crossing situation (even if they are the stand-on vessel), or when overtaking. However, in stopping they are still governed by their normal dynamics, i.e. their normal stopping distance. If you attempt to cross in front of Latitude, move with alacrity.
Because AI ships are constrained to paths, observing them allows you to predict their movement.
There is one situation where AI ships will leave their drawn paths and return: Where a path makes a sharp turn, AI ships will turn with their normal ROT, they don’t “hang a rightâ€. At such corners ships of different types will follow different paths while turning.
Regards,
Marty