East Bay (Berkeley Circle) Currents

Our current programs are unique in that we compute current at EVERY point on the Bay. The display runs in real time, refreshed every 5 seconds. The example below shows max ebb on the afternoon of September 18, 2005, at 5:12 p.m. PDT. This display option uses a streamer to show direction and gives the magnitude of the current in knots (in boxes). The blue boxes are default current locations, and the yellow boxes are additional displaypoints added by the user. You can concentrate points to show as much detail as you wish. Alternatively, you can choose the vector display, in which the length of current streamers are proportional to the magnitude of current. Although the currents in the east Bay are not as strong as in the central Bay, there are significant changes in direction over relatively short distances. As the example show, the ebb current at the north end of the Berkeley Circle flows southwest, whereas the ebb at the south end flows northwest.

These variations in current direction have a significant effect on headings, course selection and laylines. In the example below, for a short upwind leg of only 0.6 nm, it is 24 seconds faster to sail first on starboard to the lower (left-hand) layline, and then along that layline to the mark (FB), compared to a port tack and approach along the upper (right-hand) layline. (This example used 1D35 polars and assumed winds of 10 knots at 235 degM.) The blue lines from the buoy show the current-independent layline, and the magenta dots show the current-corrected layline. Note that there are two different effects of current on the layline: (1) boat motion is affected by set and drift, and (2) the motion of the water relative to the land affects the true wind seen by the boat. Due the strong and variable Bay currents, laylines are often curved. If you sail along the layline at the boat's optimal tacking angle for the (corrected) true wind, the boat will trace the curved path to the mark. Our tactical programs calculate these effects and determine the optimum route to the mark.