Data Logging

To break this project into manageable steps I've decided to make a first (in the boat) goal to record telemetry from the boat:

• apparent wind angle
• apparent wind speed
• boat speed
• GPS coordinates

It will be important to be able to consistently record these values to calibrate the sensors.

To that end I ordered a data logger shield to use with my Arduino UNO. With it I can record all the sensors on the boat. I have a bluetooth SiRF III data logger lying around somewhere that I'll also put in the boat. Both the shield and GPS time stamp and output to CVS so I should be able to get reasonable accurate telemetry.

I'll also need to find a wind vane / anemometer with trusted data output to compare to mine.

Velocity Made Good Calculation

Velocity made good (Vmg) from wikipedia is the velocity toward a mark. To compute Vmg the following quantities must be know:

• Yacht speed -- Vs
• Apparent wind direction -- (B - lambda)
• Apparent wind speed -- Va
• Leeway Angle -- lambda

"The solution of this equation electrically would require equipment both too costly and bulky forgeneral use. The further complication of correcting the measured values of Va and (B - lambda) to allowfor the errors introduced by the heeling of the yacht make an exact-solution computer impracticable." from R. N. B. Gatehouse

"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.

By trig we have:

Electronic Instruments and Computers for Sailing Yachts

by R. N. B. Gatehouse

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:

• where to put the speedometer - "the boundary layer beneath the hull of a typical racing yacht was nowhere more than 1 in. thick and was only about 1/2 in. thick at a position 5 ft. aft of the forefoot, the position finally chosen for the sensor [on a 24ft boat]."

• "The leeway angle, which is the angle between the yacht's fore-and-aft axis and the direction of motion through the water, reaches a maximum value when the yacht is close-hauled, this value varying between about 2° and about io°"

• Wind Vane Error - the error of measurement of wind direction due to sail deviation seldom exceeds 3 degrees and is independent of wind velocity.,, [other researchers], indicated that the error was about + 7 degrees.... [Moreover] The error is such as to make the apparent wind angle greater than it really is.

• Anemometer - The diameter of each cup is 1 in. and the length of its supporting arm is 1 1/2 in. Departures from linearity did not exceed 0.5 per cent within the speed range 2-60 knots.

Commenting Code

I have 5 major pieces of code that I'm trying to wrap my mind around.

• The latest Aurdpilot Mega
• Harald Molle's Modified Ardupilot v1.o
• Glenn's Wind Vane
• Robbie Edwards' code for their autonomous sailboat based on Aurdpilot Mega
• Code for the Adafruit data logger

right now I'm reading through everything and make TONS of comments. My programing skills are old minimal and rusty. I think I took 2 or 3 programing classes in college... As soon as I get a chunk commented I'll post it.

Apparent Wind angle correction for heel angle

Taken from here.

The Servos Arrived

Ordered the servos about 3 days ago from Servocity.com. I was surprised at how small and expensive they were. They were on sale (25%). Notice the 180 degree option on the first one. That is so the servo has enough travel to fully take in and let out the sheets.

Qty Description Unit Amount
--------------------------------------------------------------------------------
1 (37950S10) HS-7950TH Servo $149.99 $149.99
* Quantity Modifier $-37.50 $-37.50
* Option: Rotation is 180° (5445) $10.00 $10.00

1 (31085S00) HS-85BB Servo $19.99 $19.99
* Quantity Modifier $-5.00 $-5.00

Spruce for the Mast

Call around and Emerald Marine said they had some spruce that would work for my sailboat mast. I'd use aluminum, but its against the AMYA rules for a Soling one-design. I'd like to keep my boat legit.