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Sailboat Paddlewheel Calibration (Part II)

See my original post first. Paddlewheels are notoriously inaccurate, especially at low speeds. Even with the "ideal hull shape" calibration from my other post, the reading will still be pretty far off due to differences between my sailboat's hull, sensor location, and what B&G tested for their corrections. The only proper way forward then is to do some on the water testing with no wind and no current. How often does that happen in the San Francisco Bay? Never. But I finally found a calm morning that was pretty close. The wind was hardly there, and it was at slack tide--an extremely rare combination that, although not perfect, was the best I'd ever get. The plan: motor back and forth in a straight line in my marina, recording the NMEA stream in OpenCPN. Twice at low speed, and two more times at high speed. With each run consisting of an "up" and "down" leg, that gives me a total of 8 runs to get good data. After importing this NMEA

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