Originally Posted by mattkab
I also note that just sitting tied to the dock
, the GPS thinks the boat changing heading, and is even moving at up to .3 kts... now, there may once again be a way to filter the information to get higher quality signals. Probably worth looking into in fact.
When your gps speed is low, the heading is not reliable. Further, gps heading is the direction you are moving, not the direction the boat is facing, and also knows nothing about how the apparent wind
changes direction as you reach the crest of a wave.
Instead consider combining gps (for conditions with little wind
and waves) with a wind direction sensor. At least it can react fast enough, and also deal with subtle wind shifts, but there are limitations (besides not working when there are swells with little wind) For example:
Further, depending on where the wind direction sensor is mounted, and how it is constructed, the boat motion itself may cause the paddle to shake and it can also measure an apparent wind that is not what affects the sails appropriately. Consider the wind sensor at the back of the boat when yawing, or top of the mast
Ideally you would have wind direction sensors in several locations on the boat, and also sensors which can measure the vertical component of wind, but this is probably just not very practical.
You can use very clever filtering to probably mostly sort this type of problem out to reduce oscillations (most people who are familiar with mechanical wind vanes know about his) but still doesn't completely solve the problem.
"Bearing off at the crest prevents the stern from falling into the trough." It is difficult to determine where the crest of the wave is with only a wind direction sensor and gps, but not very difficult with accelerometers and gyroscopes. This adds considerable safety
factor, and also allows fine-tuning between a comfort/speed trade-off.
Inertial sensors are cheaper than gps and can sample at a few hundred hz easily. What is the problem with using them?