The rudder current draw information is sent back to the hand held transmitter and the pictured servo responds accordingly.
I'm on a little tangent from the original arduskipper project. 
This was a lot easier than I had imagined. I followed the Ladyada LCD tutorial and her xBee tutorial. I used the code she provided a long with the liquidcrystal library example sketch which you can find under Arduino 0022 File>Examples> LiquidCrystal>HelloWorld. To this point I can type on my computer in terminal and it will show up on the bright blue display. The connection is wireless between 2 xBees. The xBee connected to the computer used and FTDI cable and an adafruit xBee adapter. The computer just has terminal running using this tutorial. (If you want to connect to your xBee using a terminal on a Mac here's how.) The second xBee is pictured to the right.
It's code time... I've been cutting and pasting code together trying to get everything to work at the same time. I'm using a em-406a GPS on the Adafruit GPS shield. I have 2 photogates that need to use the attachinterupt() function. The only digital pins that are setup on the Arduino UNO for attacheinterupt() are 2 and 3. The GPS shield uses digital 2 and 3 for GPS communication using NewSoftSerial. So I tried moving the GPS to other pins, 8 and 9 worked. Now pins 2 and 3 are free for my photogates.
I have the photo interrupter all wired up. With the paddlewheel in place and painted black it works really well. right now all I get is RPMs. But I'll calibrate it with the GPS soon.
Its been quite a while since I last posted to Arduskipper. The project is still alive. I have been busy building a 3ft sailboat as a platform for the project. 
Here is the paddlewheel. Its a vacuform plastic housing with an acylic paddlewheel. The rod is the same carbon fiber that I used for the anemometer. I already have all the sensors working with the arduino so now all I have to do is put the pieces together. 
This is the most high-tech pinwheel I've ever made. Sealed ball bearing (with flange), Aluminum tube, Carbon fiber rod, heat molded .02" plastic cups, and cast transparent (ortho) acrylic. The cups are probably a little small at about 1in diameter. I'd like the anemometer to be sensitive to 1 knot (or less if possible) because these little boats don't sail in heavy winds. But testing larger cups later would be very easy.
A photo of my working photo interrupter. Here is the trick to getting a new photo interrupter working (tipped off by this thread). There are 2 sides to the gate; the transistor and the emitter.
int val;
void setup()
{
pinMode(13, OUTPUT);
pinMode(2, INPUT);
Serial.begin(9600); // sets the serial port to 9600
digitalWrite(13, HIGH);
}
void loop()
{
val = digitalRead(2); // read digital input pin 2
//val = analogRead(0); // read analog input pin 0
Serial.print(val); // prints the value read
Serial.print(" "); // prints a space between the numbers
delay(100); // wait 10ms for next reading
}
// I2C related constants and variables
// Library includes
#include
#define HMC6343Address 0x32
// Shift the device's documented slave address (0x32) 1 bit right
// This compensates for how the TWI library only wants the
// 7 most significant bits (with the high bit padded with 0)
int slaveAddress = HMC6343Address >> 1; // This results in the 7 bit address to pass to TWI
// Compass measurement related constants and variables
byte headingData[6];
void init_compass(void)
{
Wire.begin(); // Open I2C to HMC6343
}
void getCompassData(void)
{
int i;
Wire.beginTransmission(slaveAddress);
Wire.send(0x50); // Send a "Get Data" (0x50) command to the HMC6343
Wire.endTransmission();
delay(2); // The HMC6343 needs at least a 1ms (microsecond) delay
// after this command. Using 2ms just makes it safe
// Read the 6 heading bytes, MSB first
// The resulting 3 16bit words are the compass heading, the tilt and roll in 10th's of a degree
// For example: a heading of 1345 would be 134.5 degrees
Wire.requestFrom(slaveAddress, 6); // Request the 6 bytes of data (MSB comes first)
i = 0;
while(Wire.available() && i < headingvalue =" headingData[0]*256" tiltvalue =" headingData[2]*256" rollvalue =" headingData[4]*256" vbthetac="headingValue/10;">
Arduino + GPS Data Logger
V0.1 - (done)
V1.0
logs:
V2.0
Logs:
V3.0
sends data to a computer via xBees
To break this project into manageable steps I've decided to make a first (in the boat) goal to record telemetry from the boat:
Velocity made good (Vmg) from wikipedia is the velocity toward a mark. To compute Vmg the following quantities must be know:"Vmg is given by Vs cos gamma. The angle between the yacht's track and her fore-and-aft axis is the leeway angle lambda"
I think that the tiny 1/2 looking like sym
bol exponent position under the devision sign is 1/lambda.
I've found that reading really old research is often more interesting than the cutting edge stuff. To see how ideas develop and in just a few minutes cover decades of development is really the essence of the information age. Here is just such a paper. Gatehouse suggest measuring true position by sighting known markers to triangulate your position which was considered unfeasible . Well a GPS is a whole lot easier, but wasn't around 1970.
Gleaned Points of Importance to ArduSkipper:
A key piece of information for a sailer (human or not) is the wind direction. Glenn Langton built a small wind vane using a special ball bearing potentiometer available here. 
http://www.sailingusa.info/true_wind_calculator.htm
This simple calculation doesn't take into account leeway. Leeway is the drift of the boat to the side due to the push of the wind against the sails.
Leeway depends on:
This simple calculation doesn't take into account current. Current creates a 'water frame of reference' which is different from the 'earth frame of reference'
Earth Frame:
sine C = c/a
c = sine C * a
cosine C = b/a
b = cosine C * a
d = power - b
CD = arctangent ( c/d )
Lake Depth Survey Blog - http://diydrones.com/profiles/blogs/ardupilot-goes-into-the-water
Lots of interesting posts about the evolution of a boat used the survey the depth of lakes. He used the Ardupilot and V1.0 software, but modified it for a his boat.
Discussion regarding sailboat application - http://diydrones.com/forum/topics/imu-3000
Didn't entirely understand the conversation, but it regards drift compensation.
Required components for a Boat - http://diydrones.com/forum/topics/ardupilot-boat-requirements
User Jim Covert asks about the components need for a boat project. points out the that he'll want to use Ardupilot 1.0 which lacks stabilization control. A boat doesn't really need that feature.
Another lake survey project - http://letsmakerobots.com/node/21098
Detailed description of boat building process and application of an Arudino Duomilanove for controlling the boat.
Boat navigation with ArduPilot - http://diydrones.com/forum/topics/boat-navigation-with-adrupilot
User Tony K. asks about the components needed to pilot a sailboat. Give some direction on what is specifically needed and some specifics about GPS parameters.
Two-way Telemetry - http://diydrones.com/forum/topics/moving-waypoints-in-flight
User Peter Ho appears to be using ArduPilot on a boat and wants to change waypoints while en-route. points out that two-way is available on the ArduPilot Mega.
Everything you need for ArduPilot Boat - http://diydrones.com/notes/ArduPilot
AP for Sailing Vessel - http://diydrones.com/forum/topics/ap-for-sailing-vessel
andrew was starting a project for a auto pilot for a sailboat. He focussed on the magnetic compass. He demonstrated a working tilt compensation compass details here.
AUOOSB Open Ocean Sailboat Project - http://diydrones.com/profiles/blog/show?id=705844%3ABlogPost%3A6278...
Michael King Put up a community page at auoosb.ning.com to work toward building an autonomous sailboat. The site appears to have put on hold by NING but I believe I contacted Michael about reactivating it.
PID Tuning - http://diydrones.ning.com/forum/topics/705844:Topic:46763?xg_source...
Michael King Post on how to tune your PID settings for each craft. Not specific to boats, but PID tuning did cause Harald Molle a lot of grief in his boat project.
