I always use a stock FS plane initially when doing AI.
When you are sure everything is O.K. then bring
your ship /plane/train in its place.
If it dissapears then you know where the problem
might be.
Do you have a AFCAD for just the boats/ships ??
Could be a problem with elevation ??
or with the AI ship /plane/train. Recently I had
one that I could load as my Aircraft but will not
load as AI. I have checked eveything but it is
still not there in AI.
I have had a lot of trouble with AI ships and have
come to the conclusion I have to make my own.