How in the world do you go from 13 ° and shoveling snow off your deck to racing the next day? And what about winterizing!?
Bill Coleman Erie PA From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Randy Stafford via CnC-List Sent: Monday, October 14, 2019 11:21 AM To: cnc-list@cnc-list.com Cc: Randy Stafford Subject: Re: Stus-List Sailtimer app and racing 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 <cnc-list@cnc-list.com> 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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