Differences in how Local Knowledge treats Currents ...

TIDAL CURRENTS
Currents are often critical for competitive racing and getting them right can make a big difference in any voyage. Tidal currents vary minute to minute and can be predicted very accurately. Local Knowledge has taken current predictions to a new level and developed high-resolution hydrodynamic current models for numerous venues, around the US and worldwide. Although called "models," these predictive software programs are based on actual measurements and are continually tested by observations. In venues such as San Francisco, the "LK" model can be adjusted for seasonal variations by reference to current sensors.
All versions of LK software compute current at every point in the region. The user can add as many current display points as desired, wherever desired, and save sets of such points for recall on future occasions. In the example below, standard current points are shown in blue, with user-added points in yellow. The streamers show direction and the box indicates magnitude.
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ONLY LOCAL KNOWLEDGE HAS POINT-BY-POINT CURRENT PREDICTIONS FOR NORTH AMERICA
All LK programs can display LK currents and integrate these currents into the computation of current-corrected headings and times of transit. All programs can also apply current to compute current-corrected laylines, as in the example below. The zero-current layline is shown by the solid blue lines, and the current-corrected layline by the magenta dots. There is more to corrections than taking into account the set and drift of the boat. Current also changes the true wind experienced by the boat. In the example the corrections in the upper part of the region are inside (to the right of) the zero-current layline, even though this a flood current pushing the boat from left to right. The reason is that the strong current changes the effective wind direction, allowing the boat to sail more directly to the upwind mark (following the line of magenta dots).

NO OTHER SOFTWARE COMPUTES LAYLINE CORRECTIONS TO THIS ACCURACY.
TO THE EXTENT THAT OTHER BRANDS TAKE CURRENT INTO ACCOUNT, THEY USE AVERAGE CURRENT AND IGNORE CURRENT CHANGES POINT TO POINT ALONG THE LAYLINE.
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Knowing current point to point permits a range of computations unique to Local Knowledge. LK's Force 4 Tactical program can compute and compare time and distance to the current-corrected laylines, as shown below. The computation shows that a starboard tack from boat position to the lower layline, and then along the layline to the mark, is 6.5 minutes faster than the port tack approach. This is a huge differential in racing. At longer distances, the ability to make this computation can save a cruiser hours, and accurately predict whether you can fetch a mark.
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BOTTOM LINE:   ONLY LK HAS DETAILED TIDAL-CURRENT INFORMATION AND USES IT TO PERFORM PRECISE TACTICAL COMPUTATIONS ...
 

OCEAN CURRENTS
Ocean currents cannot be predicted in advance or modeled with any degree of accuracy. They can, however, be derived from an analysis of satellite observations of temperature, wave heights and other data. These observational models can be quite accurate, but are valid for a limited period. In the case of the Gulf Stream, the collaboration of Local Knowledge and oceanographer Jenifer Clark has produced outstanding predictions, valid for up to a week (world class navigator Stan Honey called them "astonishly accurate" in the 2002 Bermuda race).

As with tidal currents, ocean currents can vary sharply over relatively small distances (perhaps a few nm in places), and an accurate PC model has to embody a lot of detail in certain locations while still spanning hundreds of miles. Other sources try to represent currents on a grid of equally-spaced points, which is inconsistent with the actual distribution. LK takes a general approach to current distributions which does not artificially represent currents on a grid. LK models put the detail where it is needed, and LK functions only compute current at the points and times needed by the computation.
The example below is taken from the 2002 Bermuda race (the boxes show the positions of the leading boats at the first morning report, and the colored lines a part of the Force 4 routing solution). The red current vectors show the unusual u-shaped "meander" of the Gulf Stream that dominated race strategy. These current points are drawn from LK's underlying current model, which computes current at any desired point, for display or in the routing solution.

ONLY LK DOES A POINT-BY-POINT, TIME BY TIME, CURRENT COMPUTATION FOR ROUTING. ALL OTHERS USE AVERAGE CURRENTS. LK CAN DO THIS BECAUSE OF ITS MORE EFFICIENT DESIGN.
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THERE IS NO FREE LUNCH !!    Ocean current modeling is an art. Various academic and government programs which are working to predict ocean currents are ambitious, and someday may even succeed. But no ocean current predictions in the public sector are accurate enough for routing computations.
For example, MaxSea provides "free" Gulf Stream current files on its "navcenter" site, taken from government sources. These theoretical currents, however, do not even reproduce the main flow, much less the many warm and cold eddies that are significant for racing. The image below shows current vectors (in blue) taken from MaxSea on 5/5/04, overlaying the US Navy's northern GS flow diagram. These currents look OK at the lower left, but fall well below the stream and don't follow its course as the stream moves further east (left to right). These differences are huge, some 50 to 100 nm. Likewise, MaxSea currents for the 2002 Bermuda race failed to reproduce the critical U-shaped feature above. Regrettably, MaxSea does not warn users of these failings.
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BOTTOM LINE:   FOR ACCURATE OCEAN CURRENTS, GO WITH THE EXPERTS ...
THE JENIFER CLARK - LOCAL KNOWLEDGE COLLABORATION HAS PRODUCED HIGHLY ACCURATE OCEAN CURRENTS FOR RACES AROUND THE WORLD, FROM THE VOLVO, TO SYDNEY-HOBART, THE DCNAC AND THE BERMUDA RACE. WE PROVIDE CURRENTS FOR BOTH LK & 3RD-PARTY SOFTWARE.

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