I had an email debate last week with the folks who make the Sailtimer app and wireless wind instruments. They claim their app will determine optimal tacking angles and adjust them in real time. I was trying to understand what the software did and how it was doing calculations and getting very confusing (to me) answers. As an example, I asked what the software would do if there was a header. My presumption was it would detect the shift and give you some feedback or recommend tacking. It should not be hard to figure out that you are going slower toward the mark (VMG). We agreed taht VMG was problematic because it changes as you approach a mark, but their approach was equally problematic. Here is the response I got:
Headers and lifts are actually another antiquated racing method, that are very clumsy in the age of GPS and computers. They were great in the 1920s when it was impossible to do trigonometry every second in a boat heeled over and crashing through waves. But they make you choose some arbitrary length of time to get an average wind direction. And they make an assumption that the wind is going to go back to average later. If a lift happens for 2 minutes, why call that a lift and not say that it is the real wind? Too many assumptions. They are not necessary; why not just always sail on the optimal course to get you to the waypoint fastest? If the wind changes while on the proposed course, the green line moves, and you just keep on following it. There is no such thing as lifts and headers from some arbitrary time interval in which the wind direction is averaged. Your goal should be simply to always follow the optimal tacks. That answer makes absolutely no sense to me. Their optimal course is based on polars as near as I can tell. More importantly, they are arguing that there is no advantage to tacking on a header. Yes, there is a tactical argument as to whether you would tack on every shift in a large keel boat where tacks are slow relative to continuing straight, but in any significant shift, my years of racing experience plus the math of the sailing angles argues to me that Sailtimer's explanation is bogus. Am I missing something? Dave S/V Aries 1990 C&C 34+ New London, CT
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