Ok, back to the BOATS. Here's what I've come up with so far. If you've been following the thread, you know I've been converting the airplane's autopilot to work on boats.
The "airplane" autopilot turns the plane using the ailerons to tilt the plane. A boat turns by changing the angle of the rudder in the water. So, to transfer the forces from the ailerons to the rudder, you have to add a missing line to the [airplane_geometry] section. The line is :
aileron_to_rudder_scale=8.0 // (Links ailerons to rudders)
Put a value representing the scale you wish for this action. Larger values equal more rudder/less aileron. OK, so we have power to the "rudders". But alas, there are no rudders installed. So in the [contact_points] section you have to add some. They look like this:
[contact_points]
;/1 Class (0 = None, 1 = Wheel, 2 = Scrape, 3 = Skid, 4 = Float, 5 = Water Rudder)
point.13=5, -110.200, -15.50, -3.95, 9600, 0.0, 0.0, 45.0, 0.15, 0.35, 0.9, 1.2, 0.0, 0.0, 0.0, 0.0
point.14=5, -110.200, 15.50, -3.95, 9600, 0.0, 0.0, 45.0, 0.15, 0.35, 0.9, 1.2, 0.0, 0.0, 0.0, 0.0
The first number after the "=" sign is a "5". That is water rudders. Here's the link to the aircraft.cfg information from Microsoft. Bookmark this link into your browser, for a quick reference while editing your cfg files. This document explains what all the other numbers are for, as well as everything else in an aircraft.cfg file.
http://msdn.microsoft.com/en-us/library/cc526949.aspx#mozTocId942782
Now we have rudders, and the autopilot can steer them. How well it does this is another can of worms. Since the autopilot section is just a copy of a C208's autopilot, the settings are not correct for the craft you are trying to steer. Hopefully, the first thing you'll notice is the boat turning on its side, listing to the left and the right. You can tighten that up by adjusting the "bank angle". In the [autopilot] section, find the "max_bank=" line, and reduce it to some single digit number, like 2 or 5 degrees of bank. While you're there, change your "max_pitch" reference to "1.0". Or it could just keep going in a straight line. The autopilot settings are too weak to cause a reaction from the boat.
(see edit below) I have found so far, that the boat doesn't steer as well at low speeds. I am working on that problem. The lines of the [autopilot] section that begin with "nav_" are for controlling the linear navigation of the autopilot. How fast it turns, how tightly it tracks, etc. I am still experimenting with this section, to get the boat to track more tightly, and at lower speeds. The lines that start with "gs_" are what control the vertical aspects of the autopilot. (The glideslope). We have no interest in this section, being earthbound as we are, in a boat.
Autothrottle so far is a wash. I have not been successful in my attempts to control or change that. Attempting to activate autothrottle results in the engines powering down. Very strange. Still, could be useful if you wanted to "power down" your boat. (come to a stop).
(edit-It is possible for the autopilot to steer at slower speeds, I have found. By increasing the values of the rudder and aileron area, and the autopilot's proportional control constant, integrator, and derivative control constants, increasing the rudder and aileron effectiveness, increasing the aileron to rudder scale, increasing the roll and yaw stability, and rudder trim effectiveness, increasing the parasite drag scalar, decreasing the yaw damper gain(to -1500 or so). I've probably missed something in there, but if you can juggle all those numbers, throw them into the aircraft.cfg file in the right proportions, and get your boat reloaded in memory correctly, it may work. (I was so happy to see lateral movement that I felt like Dr. Frankenstein awakening the monster for the first time. "Whoo hoo!!! I think it moved. Did you see that!!!" That makes the hours on end, of trolling through the Fjords, hoping for a reaction, all worthwhile.)
Sorry this isn't a "how to" manual. I don't know yet if I can explain what I've done. Many hours of tweaking and experimentation with radical number values, just to see what happens. I wish there was a reference manual for the settings in the aircraft.cfg file that tells what are acceptable ranges or values for each item. I am stabbing in the dark with every attempt, sometimes making things better . . . and sometimes horribly worse.
That's my (updated) story so far. I hope more people start working on this problem, and we can pool our knowledge to get a "boat" with a "boat autopilot", instead of a plane that looks like a boat, and an airplane autopilot controlling it over the water. If you've made it this far, thanks for reading it. Happy tweaking!