I have a simple requirement: I want to put some ships (I have some mesh models) on a body of water, with islands, and play with various collision avoidance and command and control algorithms. So I need a environment where I can modify object behaviour but where the world and its mechanics are already coded. I was expecting that this would be trivial to find as this is such an obvious requirement for say, AI experimentation. But I haven't found anything open source or commercial. I've looked at Glest, Delta3D, Spring, Unity, ORTS, Strive, and VBS2. I looked for, but never found, the Homeworld Engine. I also found Breve, Lagoon (seemed perfect), ECSLent, but these were/are either no longer supported or documentation (if it exists) is confusing enough that it isn't clear what can/can't be done or how to go about it. Interestingly, it seems like you have to roll your own if you have a need eg. Breve, Lagoon.
So I'm putting the question to you: is there a virtual environment out there, with physics, that would allow a person to focus just on behaviour creation? What have I missed? Thanks for any guidance you can provide.