Bob, Maybe it's something you have to see to understand. Please don't take this as talking down to you, I'm simply trying to makes sure we are starting from the same baseline.
VMG (velocity made good) or sometimes CS (course speed) is the speed of approach to the next way point. If you point directly at the way point then boat speed and VMG will be matched. If you were to point away from the mark then boat speed and VMG would begin to differ. The VMG is calculated by the chartplotter performing vector geometry using cosign of the angle between your layline and your course line multiplied by boat speed. As you move along your course line, the bearing to the mark will become greater and greater. This is the function by which boat speed can increase or stay the same but VMG will decrease. Assuming wind, wave, and current conditions are all equal on both tacks and tactics are not a factor - after each gybe VMG should be maximized. The helm should work with the sail team to find the course and sail trim that gets the best VMG. Shortly after the gybe a baseline will be found and as you move along the course you will be able watch the VMG start to lower due to the increasing angle of bearing to the mark. More than 45° bearing to the mark and VMG will be less than half of current boat speed. This is the very latest point at which you would want to gybe. Now that you are maximizing VMG, you can start throwing in the other factors... Tactics probably being the most important followed by the effects of wind, waves, and current. It is on these downwind runs that other boats can sneak up behind you and steal your wind. Wind shadow can project a distance of 8 times the height of the object. The windex points to the objects that are casting shadow so look behind you for boats where the arrow is pointing. You can try to block them from shadowing you by coming upwind (away from the mark) slightly (reducing VMG)... Eventually you or your competition is going to lose the fight and have to gybe. As you approach the mark the rounding is going to have a favored side and your foredeck is going to have a lot of work so make sure to give them room to raise the head sail, douse the spin, drop the pole, stow the topping lift, round the mark, come up to the wind, and possibly tack. Reset for the next spin run. Make sense? Josh Muckley S/V Sea Hawk 1989 C&C 37+ Solomons, MD On Wed, Oct 6, 2021, 12:25 Bob Mann via CnC-List <cnc-list@cnc-list.com> wrote: > I don't understand how either answer is telling me it's time to gybe. > > Bob > > On 10/06/2021 11:37 AM Shawn Wright via CnC-List <cnc-list@cnc-list.com> > wrote: > > > I don't race, but do use VMG when trying to get our best time to > destination, especially on longer days. This works well enough in many long > channels and inlets with wind aligned with our course, but sometimes it's > not aligned. In these instances I'll have to try this trick for fooling the > VMG by giving it a waypoint at the far end of whatever channel we're > navigating. Of course, I'll have to read the B&G manual, as their UI is not > that intuitive, or things don't always work as you expect. > > -- > Shawn Wright > shawngwri...@gmail.com > S/V Callisto, 1974 C&C 35 > https://www.facebook.com/SVCallisto > > On Wed, Oct 6, 2021 at 8:30 AM Dennis C. via CnC-List < > cnc-list@cnc-list.com> wrote: > > Bob, > > First, let's define some terms. > > VMG (wind based) - the component of your velocity DIRECTLY upwind or > downwind. > > WCV - waypoint closure velocity. The component of your velocity headed > directly at your mark (assuming it's set in your GPS). This is often shown > on most GPS systems as VMG. > > Now, if you don't have an instrument system that calculates VMG, don't use > GPS VMG (WCV). The problem is that, as you approach the layline, WCV will > tend to zero. If you overstand and cross the layline, WCV will become > negative. While this is good information for when to tack or gybe, it's > usually too late. > > Here's how to fake your GPS into giving you VMG (wind based). Set a > waypoint well past the windward mark. Let's assume the race committee sets > a good W/L course with the windward mark directly upwind of the start. > Let's say the wind is from 000 and the windward mark is set at 000 for a 2 > mile leg. Enter a waypoint in your GPS at 000 20 miles out. By setting > the waypoint so far out, WCV will approximate VMG. > -- > Dennis C. > Touche' 35-1 #83 > Mandeville, LA > > On Wed, Oct 6, 2021 at 10:03 AM Bob Mann via CnC-List < > cnc-list@cnc-list.com> wrote: > > I'm fairly new to flying a spinnaker. I did it last weekend in a race and > I believe I overstood the mark as we were sailing 110 AW before the gybe > and 85 AW heading directly to the mark. > > How does one determine when to gybe? > > Bob > Thanks to all of the subscribers that contributed to the list to help with > the costs involved. If you want to show your support to the list - use > PayPal to send contribution -- https://www.paypal.me/stumurray Thanks > - Stu > > > > Thanks to all of the subscribers that contributed to the list to help with > the costs involved. If you want to show your support to the list - use > PayPal to send contribution -- https://www.paypal.me/stumurray Thanks > - Stu > > Thanks to all of the subscribers that contributed to the list to help with > the costs involved. If you want to show your support to the list - use > PayPal to send contribution -- https://www.paypal.me/stumurray Thanks - > Stu > > Thanks to all of the subscribers that contributed to the list to help with > the costs involved. If you want to show your support to the list - use > PayPal to send contribution -- https://www.paypal.me/stumurray Thanks > - Stu
Thanks to all of the subscribers that contributed to the list to help with the costs involved. If you want to show your support to the list - use PayPal to send contribution -- https://www.paypal.me/stumurray Thanks - Stu
