The SailTimer guys have additional arguments against VMG: http://sailtimerapp.com/VMG.html . Racers want to sail the route that will require the least time to get to the next mark or finish line. The problem is that the "least time route" depends on complex and dynamic variables like a boat's polars, the current wind angle and speed relative to the angle to the next mark or line, maybe even the direction and speed of any current in the water, etc. So a VMG calculated using simple geometry is too simplistic for the complex realities. Maybe some people mean "least time route" when they say "VMG", even though they are not the same thing according to that SailTimer web page and article linked from it. SailTimer's arguments make sense to me, but I don't know how sophisticated other electronics systems out there may be. The SailTimer app updates its "optimal tacking route" based on current wind data from the SailTimer wind instrument. I've yet to use it in a race to tell me when to tack, but the idea is interesting.
Best Regards, Randy Stafford S/V Grenadine C&C 30-1 #7 Ken Caryl, CO (on the hard for winter) ----- Original Message ----- From: "Jerome Tauber via CnC-List" <cnc-list@cnc-list.com> To: "cnc-list" <cnc-list@cnc-list.com> Cc: "Jerome Tauber" <jrtau...@aol.com> Sent: Monday, October 31, 2016 7:35:42 PM Subject: Re: Stus-List VMG at the helm. Why no VMG? Velocitek created the world's first GPS-based VMG tool back in 2006. VMG was also a prominent feature on the Velocitek SC-1, the ProStart’s direct predecessor. When several other companies around the world tried to copy the SC-1’s success they also included a VMG feature on their products. Velocitek’s tag line even used to be “Velocity. Made Good.” The reason why we decided to drop VMG as a feature on the ProStart is that we couldn't find any professional sailors who used this feature while racing. The main reason the pros don't like to look at VMG when they are racing is that the boat's momentum makes it difficult to use these measurements to find an optimal heading. As an example, imagine this: You are on a broad reach and then you decide to try pointing lower. Initially your speed will not change very much because of your boat's momentum. The indicated VMG will jump up (same speed as before, better angle). You are happy; the instrument seems to be telling you that soaking low was a good idea. As you hold your course steady at this new angle, your speed will eventually drop and, as you are falling off a plane, the instrument will finally come around to telling you the truth: this new, deeper angle was, in fact, a very bad idea. The trouble is that by now you are losing boats like crazy and you're going to have to head way up to get planing again; the damage is done. The above notwithstanding, these measurements can be useful for training, especially when you don't have other boats to sail against. A GPS VMG instrument can help you figure out what the optimal settings and angles are for your boat in different conditions. It's just that these things need to be figured out before you are actually racing. Our goal with the ProStart was to make an extremely easy to use instrument that only incorporated the features that pro sailors use when they are racing. There is definitely a good justification for selling a VMG product as a training tool but the feature did not fit with our brief for the ProStart. One product that is still on the market and does VMG calculation is the Rockbox by Rock City Marine. You can check out their website here: http://www.rockcitymarine.com Sent from my iPhone On Oct 31, 2016, at 8:02 PM, dwight veinot via CnC-List < cnc-list@cnc-list.com > wrote: good luck with that...you won't be fast that way; sorry Dwight Veinot C&C 35 MKII, Alianna Head of St. Margaret's Bay, NS d.ve...@bellaliant.net On Mon, Oct 31, 2016 at 4:00 PM, Charlie Nelson via CnC-List < cnc-list@cnc-list.com > wrote: <blockquote> Hey all; <blockquote> </blockquote> <blockquote> Although I have VMG (or at least its approximate equivalent) available from </blockquote> <blockquote> my Garmin 746 Chart plotter and can display it on one of my 4 Garmin </blockquote> <blockquote> displays above the companionway, I find it difficult to see it with crew in </blockquote> <blockquote> the cockpit and I don't like putting my head into the boat looking down at </blockquote> <blockquote> the chart-plotter mounted above the binnacle while I am trying my best to go </blockquote> <blockquote> hard on the wind. </blockquote> <blockquote> </blockquote> <blockquote> OK-OK--I know this hardly qualifies as a serious problem!! </blockquote> <blockquote> </blockquote> <blockquote> Nonetheless, I am looking for the simplest solution that allows me to see </blockquote> <blockquote> the VMG either on my iphone (hard to read with sunglasses on), or a 'smart </blockquote> <blockquote> watch' which may have the same problem. I realize I could use another </blockquote> <blockquote> battery powered GPS but I would need to mount it and operate it while trying </blockquote> <blockquote> to get my head in to the race at the same time. </blockquote> <blockquote> </blockquote> <blockquote> Ideally glasses with a heads-up display of it would have it in front of me </blockquote> <blockquote> no matter what else was going on. </blockquote> <blockquote> </blockquote> <blockquote> Any listers have solutions or ideas? My simpleminded thought is to put the </blockquote> <blockquote> RC or starting line in as a MOB mark and then use either the largest </blockquote> <blockquote> negative VMG upwind from it to guide me at the helm and the largest positive </blockquote> <blockquote> VMG downwind from it find the best AWA. This would likely give me the best </blockquote> <blockquote> course to steer no matter how true the course is to windward. </blockquote> <blockquote> </blockquote> <blockquote> Thanks, </blockquote> <blockquote> </blockquote> <blockquote> Charlie Nelson </blockquote> <blockquote> Water Phantom </blockquote> <blockquote> C&C 36 XL/kcb 1995 </blockquote> <blockquote> </blockquote> <blockquote> </blockquote> <blockquote> </blockquote> <blockquote> cenel...@aol.com </blockquote> <blockquote> </blockquote> <blockquote> _______________________________________________ </blockquote> <blockquote> </blockquote> <blockquote> This list is supported by the generous donations of our members. If you wish </blockquote> <blockquote> to make a contribution to offset our costs, please go to: </blockquote> <blockquote> https://www.paypal.me/stumurray </blockquote> <blockquote> </blockquote> <blockquote> All Contributions are greatly appreciated! </blockquote> <blockquote> </blockquote> _______________________________________________ This list is supported by the generous donations of our members. If you wish to make a contribution to offset our costs, please go to: https://www.paypal.me/stumurray All Contributions are greatly appreciated! </blockquote> _______________________________________________ This list is supported by the generous donations of our members. If you wish to make a contribution to offset our costs, please go to: https://www.paypal.me/stumurray All Contributions are greatly appreciated!
_______________________________________________ This list is supported by the generous donations of our members. If you wish to make a contribution to offset our costs, please go to: https://www.paypal.me/stumurray All Contributions are greatly appreciated!
