Hi Dave, Interesting discussion.
My experience with SailTimer has been mixed. I bought their Wind Instrument a few years ago and it only lasted a couple seasons because the battery went flat. So I bought their rechargeable battery version in January and they still haven’t delivered it. I still like their concepts and price, but their product and service performance has been disappointing. Now to your discussion. I can appreciate their points that individual wind shifts are just parts of the overall average wind direction, and how do you know in a given shift whether it represents the “real” wind direction. Incidentally that average wind direction seems to be a major factor underlying their “optimal course” concept. I hope they are constantly updating their notion of average wind direction as they measure the instantaneous true wind direction and shifts in it. Having said that, I got my ass kicked in a race just yesterday because other sailors played the wind shifts better than I did. Our wind at Chatfield was oscillating at least 30 degrees yesterday, and some boats guessed right while others didn’t. So I vehemently disagree that headers and lifts are “another antiquated racing method.” That’s a pretty cavalier statement. And I think the shorter the distance from your current position to the next waypoint, the more important they become. I could understand in an ocean race from say Newport to Bermuda you might want to give the shifts some time to average out. But on a lake the size of Chatfield where the windward mark might be only half a mile from the start line, every shift is important. Cheers, Randy Stafford S/V Grenadine C&C 30 MK I #7 Ken Caryl, CO > On Oct 14, 2019, at 7:06 AM, David Knecht via CnC-List > <[email protected]> wrote: > > 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 > > <pastedGraphic.tiff> > > _______________________________________________ > > Thanks everyone for supporting this list with your contributions. Each and > every one is greatly appreciated. If you want to support the list - use > PayPal to send contribution -- https://www.paypal.me/stumurray >
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