Central Bay 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 flood on the morning of September 18, 2005, at 11:20 a.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. Note the dramatic changes in current strength and direction over relatively short distances.

The strong variation of current at different points of the Bay has a huge effect on headings, course selection and laylines. In the example below, the boat is tacking upwind to approach the Blackaller buoy (16) near Fort Point. The blue lines from the buoy show the current-independent layline for typical Bay winds of 15 knots at 235 degM. 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.