stanhoney

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About stanhoney

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  1. stanhoney

    gyro autopilot compas heading

    I mentioned the upwind approach that I use, which is for the autopilot to use both AWA and Boatspeed, when sailing upwind. The AWA and Boatspeed target numbers are actually looked up from a table using TWS as an index into the table. The AWA "target" is used as a maximum AWA, and the Boatspeed target is used as a maximum boatspeed. One way of thinking of the algorithm is the pilot will bear off to the AWA number in order to get to the BS number, and then as the boatspeed increases, the pilot will pinch up as necessary to avoid sailing faster than the BS number. So in the table you don't actually list the AWA number at which the boat normally sails upwind, instead you use ideal AWA to use to accelerate. That might be 40 degrees. In a terrible seastate the pilot will sail at that AWA as long as the BS remains slow of the BS target. This approach solves two problems. It solves the problem of a boat sailing too fast upwind in light air and flat water, and ending up reaching around at fat TWA's. It also solves the problem of a boat bearing off too far in a bad seastate, attempting to get to an upwind target BS that is not achievable in that bad seastate.
  2. stanhoney

    gyro autopilot compas heading

    I rarely post, so I'm preparing for the ritual newbie insults. On high performance boats, if the autopilot steers to a constant TWA offwind, it also needs to monitor boatspeed. The reason is that on high performance boats, you can end up with the boat on the desired TWA, but far too slow with the AWA far too deep. That can be a stable condition from which a pilot that only uses TWA will never recover because the boat will never speed up when sailing at such a deep AWA. Of course good human drivers keep an eye on the target boatspeed and in that low and slow situation (even though at target TWA) would immediately head up, speed up, and then as the boat accelerates and the AWA goes forward, they come down again to the (same) target TWA, but at near the target boatspeed. When sailing offwind in wind speed that is light and puffy, especially in flat water, having the pilot steer to a constant AWA can sometimes work pretty well, because the sail trim stays correct as the pilot deals with the puffs and lulls and the boat speeds up and slows down. Using the constant AWA mode in light and puffy air, the boat heads up at the beginning of a puff when the AWA goes aft, and heads off as the boat accelerates in the puff as the AWA goes forward.. The target AWA in these situations would be well ahead of the beam. When sailing upwind in high performance boats, Moon (as usual) is right that the pilot needs to steer by AWA, but on high performance boats the autopilot also needs to monitor boatspeed. The reason is that if the water is really flat, a high performance boat will start to sail too fast, which causes the AWA to go forward, and the boat to bear off, until it ends up reaching around at a speed far above the upwind target BS, at far too low of a TWA to make much progress upwind. Human drivers of course avoid this by keeping an eye on the target UW boatspeed and not exceeding it by pinching up as necessary. The wrinkles above are only problems for relatively fast boats, i.e. SC70 or faster.
  3. stan - thanks a lot for posting in the forum! it is much appreciated. if you have anything you want on the front page - e-mail me - editor@sailinganarchy.com