CAN YOUR SOFTWARE DO THIS?
|NEW ADVANTAGE "BEST TACK" FUNCTION GOES FAR BEYOND "WHAT-IF" CALCULATIONS ...|
|The most common situation
in racing is tacking to an upwind mark (or jibing to a downwind mark). The only tactical
information provided by other software is usually referred to as a "what-if"
function. This computes times to the mark for an approach via either layline (first a port
tack, or first a starboard tack). The image below shows the result of a typical
"what-if" computation, using the 'Enter Data' option button. The form fills in
the latest wind data, but allows you to change it to see the effect of a windshift. The
form also fills in average current across the venue drawn from the "Local
Knowledge" current model. You can modify average current, to see how this affects
results, or enter values from scratch (say, in a venue without current data).
WHAT-IF COMPUTATIONS COMPLETELY MISS THE EFFECT OF DIFFERENTIAL CURRENTS !!
When current varies across the venue, it changes both the "true" wind experienced by the boat and exerts a different push on the boat from point to point. In general, this will result in an advantage to an approach via one layline or the other. Other program "what-if" computations use an average current across the venue. This greatly simplifies the calculation but washes out the difference between tacks. In this example the blue lines show the layline as it would be with zero current, and the red lines show the result of the "what-if" calculation. The magenta dots, however, show the actual laylines, which are curved as the result of differences in current point to point (blue vectors). For discussion of differential currents, CLICK HERE.
|RESULT OF TYPICAL "WHAT-IF" SOLUTION, UPWIND AGAINST 2 KNOTS OF OPPOSING CURRENT|
|Our Advantage Racing software is UNIQUE in its ability to do exact computations in the presence of differential currents. When you average current, the time via either layline is always the same. In reality, there can be very significant differences. In this example (using J35 polars), the exact result shows an advantage of ALMOST 3 MINUTES for a initial port tack followed by an approach along the upper, curved layline (below). When you click the "Use Instrument Data" button, the "best-tack" function uses the current model and the latest instrument data and does the full computation. The result identifies the port tack solution as optimal (note that time to the mark is also significantly different from the "what-if" result above).|
|RESULT OF OUR "BEST TACK" FUNCTION, FOR EXACT SOLUTION SHOWING PREFERRED APPROACH|
"WHAT IF" COMPUTATION DOWNWIND AGAINST EBB CURRENT
|Below is a similar result downwind against an adverse current. Note that the current-modified (red) laylines computed by the (approximate) "what-if" calculation moves the layline TOWARDS the boat, despite the adverse current. This result, which seems counter-intuitive, is because the "true wind" experienced by the boat is increased by the effect of the ebb current. However, the use of average current misses the actual laylines (magenta dots) and, as always, results in identical times for port and starboard tack approaches to the mark.|
OUR "BEST TACK" RESULT, GIVING THE EXACT DOWNWIND SOLUTION SHOWING OPTIMAL JIBE
CAN YOU AFFORD TO MISS THIS KIND OF INFORMATION IN A RACE ??
These computations are difficult, but are necessary in order to obtain dependable results which maximize information to the racer. ONLY "Local Knowledge" has made the effort to do them correctly, and these functions are now standard in our Advantage software. NOTE ALSO: These calculations are updated automatically every few seconds and adjusted for windshifts as they occur.