Currents are a major factor in most U.S. (and many foreign) venues, and have a significant, sometimes dramatic, effect on laylines and routing. In this example, the magenta dots show the actual laylines in presence of currents that vary point to point (differential currents). The dashed lines emanating from the boat token show how the boat's motion on either tack is likewise affected by currents.

A few 3rd-party programs are licensed to use LK currents, enabled by LK's interpretive software (the LK "DLL"). To do so, the user must purchase the DLL and data support from Local Knowledge. This provides the same current information that is automatically incorporated in all LK programs (including Offchart Racer and Force 4). However, these 3rd-party programs use current in an approximate way, simplifying computations by averaging currents.

One example occurs often in racing: determining the fastest way to approach a mark. In constant (or zero) current, any combination of tacks takes you to the mark in the same total time. When currents change point to point, there can be a significant difference between alternative routes. For description, CLICK HERE

The 2006 edition of "OR" includes the Force 4 "Best Tack" function, which compares total time for a tack to either layline, and from the intercept along the layline to the mark. All other programs use average currents, an approximation which wipes out the distinction between different tacks and yields no tactical information. For more detail regarding "Best Tack," CLICK THIS LINK: CAN YOUR SOFTWARE DO THIS ??